Công nghiệp 4.0 là xu hướng tự động hóa và trao đổi dữ liệu hiện tại trong công nghệ sản xuất. Nó bao gồm các hệ thống không gian mạng, mạng lưới vạn vật kết nối Internet và điện toán đám mây.[1][2][3][4]

Công nghiệp 4.0 tạo ra cái gọi là “nhà máy thông minh”. Trong các nhà máy thông minh có cấu trúc kiểu mô-đun, các hệ thống vật lý trực tuyến giám sát các quy trình vật lý, tạo ra một bản sao ảo của thế giới vật lý và đưa ra các quyết định phân cấp. Qua Internet of Things, các hệ thống không gian mạng-vật lý truyền thông và hợp tác với nhau và với con người trong thời gian thực, và thông qua Internet of Services, cả các dịch vụ nội bộ và tổ chức giữa các bên tham gia chuỗi giá trị được cung cấp và sử dụng.

Công nghiệp 4.0
Công nghiệp 4.0

Tên gọi

Thuật ngữ “Công nghiệp 4.0” bắt nguồn từ một dự án trong chiến lược công nghệ cao của chính phủ Đức, nó thúc đẩy việc sản xuất vi tính hóa sản xuất.[5]

Một số đã so sánh Công nghiệp 4.0 với cuộc cách mạng Công nghiệp lần thứ tư. Tuy nhiên, điều này đề cập đến một sự chuyển đổi có tính hệ thống bao gồm tác động lên xã hội dân sự, cơ cấu quản trị và bản sắc con người, ngoài các chi nhánh kinh tế / sản xuất. Cuộc cách mạng công nghiệp đầu tiên đã huy động việc cơ giới hóa sản xuất sử dụng nước và hơi nước; Cuộc cách mạng kỹ thuật số] và việc sử dụng các thiết bị điện tử và công nghệ thông tin để tiếp tục tự động hoá sản xuất[6] Thuật ngữ “Cách mạng công nghiệp lần thứ tư” Đã được áp dụng cho sự phát triển công nghệ quan trọng một vài lần trong 75 năm qua, và là để thảo luận về học thuật.[7][8][9] Công nghiệp 4.0, mặt khác, tập trung vào sản xuất đặc biệt trong bối cảnh hiện tại, và do đó là tách biệt với cuộc cách mạng công nghiệp lần thứ tư về phạm vi.

Thuật ngữ “Công nghiệp 4.0” đã được hồi sinh vào năm 2011 tại Hội chợ Hannover[10] Vào tháng 10 năm 2012, Nhóm Công tác về Công nghiệp 4,0 trình bày một loạt các khuyến nghị về thực hiện Công nghiệp 4.0 cho chính phủ liên bang Đức. Các thành viên của Nhóm Công nghiệp 4.0 được công nhận là những người cha sáng lập và là động lực đằng sau Industry 4.0.

Các nhóm làm việc Công nghiệp 4.0 [11]

Đồng chủ tọa Henning Kagermann và Siegfried Dais
WG 1 – Nhà máy thông minh: Manfred Wittensteinê
WG 2 – Môi trường thực: Siegfried Russwurm
WG 3 – Môi trường Kinh tế: Stephan Fische
WG 4 – Nhân tính và Công việc: Wolfgang Wahlster
WG 5 – Tác nhân Công nghệ: Heinz Derenbach

Thành viên nhóm Công tác Cách mạng 4.0

Reinhold Achatz, Heinrich Arnold, Klaus Träger, Johannes Helbig, Wolfram Jost, Peter Leibinger, Reinhard Floss, Volker Smid, Thomas Weber, Eberhard Veit, Christian Zeidler, Reiner Anderl, de:Thomas Bauernhansl, Michael Beigl, Manfred Brot, Werner Damm, Jürgen Gausemeier, Otthein Herzog, Fritz Klicke, Gunther Reinhart, Bernd Scholz-Reiter, Bernhard Diener, Rainer Platz, Gisela Lanza, Karsten Ortenberg, August Wilhelm Scheer, Henrik von Scheel, Dieter Schwer, Ingrid Sehrbrock, Dieter Spatz, Ursula M. Staudinger, Andreas Geerdeter, Wolf-Dieter Lukas, Ingo Rühmann, Alexander Kettenborn và Clemens Zielinka.

Vào ngày 8 tháng 4 năm 2013 tại Hội chợ Hannover, báo cáo cuối cùng của Nhóm Công tác 4.0 đã được trình bày.[12]

Những nguyên tắc thiết kế

Có 4 nguyên tắc thiết kế trong công nghiệp 4.0.Những nguyên tắc này hỗ trợ những công ty trong việc định dạng và thực hiện những viễn cảnh của công nghiệp 4.0

  • Khả năng tương tác: Khả năng giao tiếp và kết nối của những cỗ máy,thiết bị,máy cảm biến và con người kết nối và giao tiếp với nhau qua mạng lưới vạn vật kết nối internet hoặc mạng lưới vạn người kết nối internet.
  • Minh bạch thông tin: Khả năng của những hệ thống thông tin để tạo ra 1 phiên bản ảo của thế giới thực tế bằng việc làm giàu những mô hình nhà máy kỹ thuật số bằng dữ liệu cảm biến. Điều này yêu cầu sự tập hợp những dữ liệu cảm biến thô đến thông tin ngữ cảnh có giá trị cao hơn.
  • Công nghệ hỗ trợ: Đầu tiên khả năng của những hệ thống hỗ trợ con người bằng việc tập hợp và hình dung thông tin một cách bao quát cho việc tạo những quyết định được thông báo rõ ràng và giải quyết những vấn đề khẩn cấp qua những ghi chú ngắn gọn. Thứ nhì, khả năng của những hệ thống không gian mạng-vật lý để hỗ trợ con người thực hiện những nhiệm vụ cái mà không dễ chịu, tốn quá nhiều sức lực hoặc không an toàn đối với con người.

Sưu tầm: https://vi.wikipedia.org

Câu hỏi

Đối tượng nào phải lắp đặt hệ thống quan trắc nước thải, khí thải tự động?

Trả lời

Nghị định số 38/2015/NĐ-CP

Nghị định số 38/2015/NĐ-CP là văn bản pháp luật quy định về đối tượng phải lắp đặt hệ thống quan trắc tự động, đây là văn bản trực tiếp nhất.

Quan trắc nước thải tự động

  • Các khu công nghiệp phải lắp đặt hệ thống quan trắc nước thải tự động liên tục, truyền số liệu trực tiếp cho Sở Tài nguyên và Môi trường địa phương. Khoản 2, điều 39.
  • Các cơ sở sản xuất, kinh doanh, dịch vụ nằm ngoài khu công nghiệp có quy mô xả nước thải từ 1.000 m3/ngày đêm trở lên (không bao gồm nước làm mát), phải lắp đặt hệ thống quan trắc nước thải tự động liên tục và truyền số liệu trực tiếp cho Sở Tài nguyên và Môi trường địa phương. Khoản 3, điều 39.
  • Khuyến khích các cơ sở sản xuất, kinh doanh dịch vụ nằm ngoài khu công nghiệp có quy mô xả thải dưới 1.000 m3/ngày đêm (không bao gồm nước làm mát) và có nguy cơ tác hại đến môi trường lắp đặt thiết bị quan trắc nước thải tự động liên tục. Khoản 4, điều 39.

Quan trắc khí thải tự động

  • Chủ nguồn thải khí thải công nghiệp thuộc danh mục các nguồn khí thải lưu lượng lớn quy định tại Phụ lục của Nghị định này phải lắp đặt thiết bị quan trắc khí thải tự động liên tục, truyền số liệu trực tiếp cho Sở Tài nguyên và Môi trường địa phương.
  • Phụ lục Danh mục các nguồn thải khí thải lưu lượng lớn (ban hành kèm theo Nghị định số 38/2015/NĐ-CP ngày 24 tháng 4 năm 2015 của Chính phủ).

STT

Loại hình

Đặc điểm

1

Sản xuất phôi thép Sản lượng lớn hơn 200.000 tấn/năm

2

Nhiệt điện Tất cả, trừ nhà máy nhiệt điện sử dụng nhiên liệu khí tự nhiên

3

Xi măng Tất cả

4

Hóa chất và phân bón hóa học Sản lượng lớn hơn 10.000 tấn/năm

5

Công nghiệp sản xuất dầu mỏ Sản lượng lớn hơn 10.000 tấn/năm

6

Lò hơi công nghiệp Sản lượng lớn hơn 20 tấn hơi/giờ

 Thao khảo:

Câu hỏi

Hiện tại thiết bị quan trắc tự động (nước thải, khí thải) có cần kiểm định, hiệu chuẩn không? Cơ quan nào thực hiện công việc này, văn bản nào quy định cụ thể?

Trả lời

Kiểm định thiết bị quan trắc tự động

Thiết bị quan trắc tự động phải được kiểm định theo quy định tại CV số 3031/BTNMT-TCMT. Các thiết bị đo phải được kiểm định ban đầu trước khi đưa vào sử dụng chính thức, kiểm định định kỳ 12 tháng trong quá trình sử dụng và kiểm định sau sửa chữa. Sao lục CV số 3031/BTNMT-TCMT ngày 26/7/2016 của Bộ Tài nguyên và Môi trường v/v hướng dẫn thực hiện hoạt động kiểm định, hiệu chuẩn thiết bị đo của trạm quan trắc tự động, liên tục

Các thiết bị quan trắc tự động cần kiểm định, hiệu chuẩn

Thiết bị quan trắc nước thải tự động

Thiết bị đo pH, EC, DO, Độ đục, TDS

Thiết bị quan trắc khí thải tự động

Thiết bị đo: SO2, NO, NO2, CO, CO2, hàm lượng bụi

Tất cả các thiết bị không thuộc danh mục kiểm định ở trên, có ảnh hưởng đến độ chính xác của kết quả quan trắc, thì phải được hiệu chuẩn trước khi đưa vào sử dụng và phải được hiệu chuẩn định kỳ theo đúng khuyến cáo của nhà sản xuất.

Đơn vị có chức năng kiểm định thiết bị quan trắc tự động

Các đơn vị đã đăng ký hoạt động kiểm định, hiệu chuẩn, được chỉ định thực hiện kiểm định và có phạm vi, năng lực phù hợp theo Thông tư số 24/2013/TT-BKHCN ngày 30 tháng 9 năm 2013 của Bộ Khoa học và Công nghệ quy định về hoạt động kiểm định, hiệu chuẩn, thử nghiệm phương tiện đo, chuẩn đo lường.

Có thể tham khảo thêm

Những điểm mới về xử phạt vi phạm hành chính trong lĩnh vực bảo vệ môi trường quy định ở Nghị định số 155/2016/NĐ-CP so với Nghị định 179/2013/NĐ-CP, nội dung này trích dẫn từ website http://vea.gov.vn của Tổng cục Môi trường, theo ông Hoàng Văn Vy, Phó Cục trưởng Cục Kiểm soát ô nhiễm, Tổng cục Môi trường.

Nghị định 155/2016/NĐ-CP xây dựng trên cơ sở rà soát thực tế 4 nhóm hành vi vi phạm, đó là:
  1. Các hành vi vi phạm gây ô nhiễm môi trường.
  2. Các hành vi vi phạm về quản lý chất thải.
  3. Các hành vi vi phạm liên quan đến công trình bảo vệ môi trường.
  4. Các hành vi vi phạm mang tính thủ tục hành chính.

Những điểm mới ở Nghị định 155/2016/NĐ-CP

  • Mức phạt tăng xả nước thải vượt Quy chuẩn Việt Nam từ 10% đến 50% của khung phạt.
  • Kết quả quan trắc tự động được làm căn cứ để xác định hành vi xả thải vượt QCVN.
  • Quan trắc môi trường định kỳ do đơn vị không được cấp giấy chứng nhận đủ điều kiện bị xử phạt như không QTMT.
  • Bổ sung mức phạt tăng thêm 30% nếu trong nước thải vượt quy chuẩn có chứa 01 trong 03 loại vi khuẩn (Salmonella, Shigella, Vibrio cholerae).
  • Đặc biệt, Nghị định quy định nếu tổ chức, cá nhân thực hiện không đúng nội dung đánh giá tác động môi trường (ĐTM) nhưng làm cho môi trường tốt hơn không bị phạt.
  • Đặc biệt, Nghị định số 155/2016/NĐ-CP đã xây dựng riêng Điều 53 quy định trách nhiệm và cơ chế phối hợp của các Bộ, ngành và Ủy ban nhân dân các tỉnh, thành phố trực thuộc Trung ương trong công tác kiểm tra, thanh tra và xử phạt vi phạm hành chính trong lĩnh vực bảo vệ môi trường. Việc kiểm tra, thanh tra và xử phạt vi phạm hành chính trong lĩnh vực BVMT phải bảo đảm nguyên tắc không chồng chéo; không làm ảnh hưởng đến hoạt động bình thường của cá nhân, tổ chức vi phạm. Một năm chỉ có một đoàn kiểm tra hoặc thanh tra trong lĩnh vực bảo vệ môi trường tại một cơ sở, doanh nghiệp, trừ trường hợp kiểm tra, thanh tra đột xuất theo quy định của pháp luật.

Khung phạt và mức phạt vi phạm hành chính trong lĩnh vực bảo vệ môi trường

Mức phạt được quy định tại Nghị định 155/CP là mức phạt đối với cá nhân. Mức đối với tổ chức gấp hai lần so với quy định tại Nghị định. Đối với các thành phố trực thuộc Trung ương có thể thông qua mức phạt lên gấp 02 lần so với quy định chung.
Khung phạt xả thải là số lần vượt cao nhất để làm căn cứ xác định khung phạt; Trường hợp có nhiều thông số vượt, tùy theo mức vượt sẽ tăng thêm từ 10% đến 50% nhưng không quá khung phạt cao nhất. Trường hợp có nhiều điểm xả thải thì đơn vị sẽ bị xử phạt theo từng điểm xả thải. Đồng thời đơn vị vi phạm phải chi trả kinh phí trưng cầu giám định mẫu môi trường vượt quy chuẩn.

Lưu ý về xử phạt vi phạm hành chính

Mọi vi phạm hành chính phải đình chỉ, lập biên bản vi phạm hành chính. Trong thời hạn 7 ngày kể từ ngày lập biên bản, cơ quan có trách nhiệm phải ban hành quyết định xử phạt.
Có khá nhiều đối tượng có thẩm quyền lập biên bản vi phạm hành chính. Việc này nhằm tăng cường giám sát thực hiện bảo vệ môi trường tại nhiều lĩnh vực, nhiều địa điểm. Cụ thể:
  • Người có thẩm quyền xử phạt vi phạm hành chính trong lĩnh vực bảo vệ môi trường đang thi hành công vụ;
  • Cán bộ, viên chức đang thi hành nhiệm vụ bảo vệ môi trường của Bộ TNMT, Tổng cục Môi trường;
  • Sở TNMT, Chi cục Bảo vệ môi trường;
  • Ban quản lý khu kinh tế, khu công nghiệp, khu chế xuất;
  • Phòng TNMT.
  • Các cán bộ công chức đang thi hành nhiệm vụ BVMT của các bộ, cơ quan ngang bộ; cán bộ, công chức xã, phường, thị trấn đang thi hành nhiệm vụ BVMT trên địa bàn quản lý cũng có thẩm quyền lập biên bản vi phạm hành chính.
  • Ngoài ra, còn có chiến sĩ công an, công an xã, phường, thị trấn và cán bộ trật tự công cộng đang thi hành nhiệm vụ liên quan đến BVMT tại khu đô thị, khu chung cư, thương mại, dịch vụ hoặc nơi công cộng; cán bộ, công chức, viên chức thuộc Ban quản lý rừng, vườn Quốc gia, khu bảo tồn thiên nhiên, khu dự trữ sinh quyển đang thi hành nhiệm vụ bảo vệ môi trường.

Download tài liệu môi trườngDownload Nghị định số 155/2016/NĐ-CP

Nitric oxide (NO) – Cách thu mẫu và phân tích

Introduction

The procedure for the air sample collection and analysis of nitric oxide (NO) is described in OSHA Method No. ID-190 (11.1.). The NO sample is collected using a three-tube sampling device.

This method has been evaluated near the OSHA Transitional Permissible Exposure Limit (PEL) for 240-min samples. At the time of this study, the Time Weighted Average (TWA) PEL for NO is 25 ppm. The Final Rule PEL is also 25 ppm as a TWA.

Test atmospheres were generated and samples were collected and analyzed according to the procedures listed below.

Generation System

All generations of NO test atmospheres, and hence all experiments, with two exceptions, were performed using the apparatus shown in Figure 1. The analysis (Section 1) and detection limit experiments did not use a test atmosphere generation for sample preparation. Instead, samples were spiked with solutions of sodium nitrite. For further details regarding the detection limit experiment, see reference 11.2.

A cylinder of NO in nitrogen (1.05% NO, Air Products and Chemicals, Long Beach, CA) was used as the contaminant source. The NO was mixed, using a glass mixing chamber, with filtered, tempered air. A flow, temperature, and humidity control system (Miller-Nelson Research Inc., Model HCS-301) was used to condition the diluent air for mixing. A Teflon sampling manifold was attached to the mixing chamber. Flow rates for the diluent air were determined using a dry test meter. Contaminant gas flows were measured using mass flow controllers and soap bubble flowmeters.

Sample Collection

Air samples were collected from the Teflon manifold using calibrated SKC Model 222-3-10 low-flow pumps (approximately 0.025 L/min flow rate) during all generation experiments. Two different TEA-IMS sampling devices were commercially available for NO sampling at the beginning of the validation. The two devices listed below are designed to simultaneously collect NO2 and NO. Preliminary studies indicated the SKC collection device (1) was the most suitable for collection of NO and NO2:

  1. SKC NO2-NO collection device (SKC Cat. No. 226-40, water-washed):
    The sampling device consists of three separate glass tubes. A description of the tubes is given in reference 11.1.The SKC tubes used for all validation experiments were from lot no. 374 except for the storage stability experiment where lot no. 444 tubes were used.
  2. Supelco combination tube:
    This combination tube contains all three sections in a single tube. Two 400-mg sections of TEA-IMS are separated by an oxidizer section. The Supelco tube uses a smaller mesh size of molecular sieve and only approximately 800 mg of oxidizer. Tubes from lot no. 564-07 were only used for a preliminary sampling and analysis experiment. Due to the low recoveries found during this preliminary study, further experiments using the Supelco combination tube were not performed.

Sample analysis

Note: The analytical portion of the method for NO is the same as the NO2 method; both analyses are performed by determining the amount of NO2 produced from the NO2-TEA reaction.

Samples prepared for all experiments were analyzed by IC using the conditions specified in the method (11.1.). For the conversion of NO2 to nitrite, a conversion factor (C.F.) of 0.72 was first reported (11.3.). Later experiments indicated an average C.F. of 0.63 (11.2., 11.4.-11.5.). The 0.63 C.F. was used for all experiments in this evaluation which were conducted with concentrations less than 10 ppm NO. A C.F. of 0.5 was used for concentrations above 10 ppm NO.

Sample Results

Results were calculated using peak areas and linear regression concentration-response curves. A statistical protocol (11.6.) was used to evaluate results. Any calculation of error follows the general formula:

Errori = ± [|mean biasi| + 2CVi] × 100%           (95% confidence)

where i is the respective sample pool being examined

Data were subjected to the Bartlett’s test (11.7.) and a test for outliers (11.8.) to determine homogeneity of variance and identify any outliers. Both tests were conducted using the 99% confidence level.

Validation

The following experiments were conducted for the validation of Method No. ID-190:

  • Analysis – Desorption efficiency (DE) of spiked samples
  • Sampling and Analysis – generation and analysis of NO samples
  • Collection efficiency
  • Breakthrough tests.
  • Storage stability.
  • Sampling at different humidities.
  • Determination of the conversion factor for NO concentrations of 10 to 200 ppm.
  • Sampling and analysis of a mixture of NO and NO2.

This analytical method was also compared to the polarographic method previously used by the OSHA laboratory. This method comparison and the detection limit determinations were performed during the NO2 method validation (See reference 11.2. for more information). The quantitative detection limit was determined to be 0.08 µg/mL (as NO2).

A preliminary sampling and analysis experiment using Supelco tubes was also performed and is discussed in Section 9.

  1. Analysis (Desorption Efficiency, DE)

Procedure: Eighteen spiked samples (6 samples at each test level) were prepared and analyzed. Samples were prepared by spiking known amounts of sodium nitrite solutions into TEA-IMS treated solid sorbent tubes. Calibrated micropipettes were used for spiking. The spiked concentrations corresponded to approximately 12.5, 25, and 50 ppm of NO when using a 0.025 L/min sampling rate for 240 min. These concentrations are approximately 0.5, 1, and 2 times the OSHA PEL.

Results: The results are listed in Table 1. Recoveries at these levels represent analytical DE. Results also provide recoveries, analytical error (AE), and extent of variability for the analytical portion of the method.

All analysis data passed the Bartlett’s and outlier tests. Sample results were pooled. The analytical data for the method (Table 1) gave acceptable precision and accuracy (11.7.) and does not indicate a need for a desorption correction factor. The coefficient of variation for analysis (CV1) was 0.045 and the average analytical recovery was 107.3%.

  1. Sampling and Analysis

Procedure: A total of 20 samples were collected from dynamically generated test atmospheres and analyzed. The concentrations generated were about 0.5, 1, and 2 times the PEL. The generation system shown in Figure 1 was used. Samples were taken for 240 min at a RH and temperature of 50% and 25°C, respectively.

Results: The results, as shown in Table 2, provide the overall error (OE) and precision of the sampling and analytical method. Overall error should be less than ±25% when calculated using the equation listed in the Introduction.

The Sampling and Analysis data show acceptable precision and accuracy (11.7.). All data passed both the outlier and Bartlett’s test and the results were pooled. The coefficients of variation for spiked CV1 (pooled) samples, generated CV2 (pooled) samples and overall CVT (pooled) are:

CV1 (pooled) = 0.045,     CV2 (pooled) = 0.080,     CVT (pooled) = 0.082

The sampling and analytical bias was +3.3%. Overall error was within guidelines (< ±25%) and was ±19.7%.

  1. Collection Efficiency

Procedure: Dynamically generated samples were used to measure the sorbent collection efficiency at the upper concentration limit (50 ppm NO) of the validation. Six SKC sampling devices were connected to backup TEA-IMS tubes using Tygon tubing. This sampling train was configured using the following tube sequence:

1) TEA-IMS       2) oxidizer       3) TEA-IMS       4) TEA-IMS

This train was used to collect NO at 2 times the OSHA PEL for 240 min. A pump flow rate of approximately 0.025 L/min was used. The amount of NO collected in each TEA-IMS tube was measured.

Results: Results are reported in Table 3. The collection efficiency was calculated as:

% Collection Efficiency = µg NO found in tube 3

µg NO found in tube 3 + tube 4

× 100%

Collection efficiency was 100% at 2 times the PEL, which indicates the sorbent media has adequate capacity for collecting NO within the validation range.

  1. Breakthrough

Procedure: Test atmospheres were generated at a concentration greater than the validation level to determine if any breakthrough of NO occurs from the primary solid sorbent sampling tube (following the oxidizer) into a second tube. Breakthrough is considered significant if the concentration collected with the second tube is >5% of the results from the first tube. Twelve sampling devices were connected to backup tubes (as mentioned in Section 3.) and then to sampling pumps. All samples were collected at a concentration of 200 ppm and 0.025 L/min flow rate. Three sampling devices were removed from the generation system at 60, 120, 180, and 240 min. The generation system was set at 30% RH and 25°C. The low humidity level was used as a “worst case” test since the presence of water is necessary for the conversion reaction of NO2to NO2 to proceed (11.1., 11.4.).

Results: Results are shown in Table 4. The extent of breakthrough was assessed by:

% Breakthrough = µg NO found in tube 4

µg NO found in tube 3 + tube 4

× 100%

Breakthrough studies indicate the SKC sorbent tube and oxidizer capacity for NO is adequate for air concentrations up to 200 ppm when using air volumes and flow rates described. Further research to determine the actual breakthrough concentration was not conducted. It should be unlikely that industrial environments will exceed an exposure of eight times the PEL.

  1. Storage Stability

Procedure: A study was conducted to determine if any storage problems existed for TEA-IMS tubes which had been used to collect samples. The procedure used is discussed below:

  1. Twelve samples were collected at the OSHA PEL as described in the Introduction.
  2. These samples were stored at 20 to 25°C on a laboratory bench for the duration of the storage period.
  3. Three samples were analyzed at 0, 5, 15, and 30 days.

Results: The results of the storage stability study are shown in Table 5. The mean of samples analyzed after 30 days was within ±5% of the mean of samples analyzed after 1 day. Samples may be stored in environmental conditions found in a laboratory setting for 30 days without a significant change in results.

  1. Humidity Study

Procedure: A study was conducted to evaluate any effects on recovery when sampling at different humidities. Contaminant atmospheres conditioned at 30, 50, and 80% RH were generated at 25°C. Six or seven SKC sampling devices were used at each RH level.

Results: Results are shown in Table 6. Data from sampling at different humidities displayed an apparent effect on sampling efficiency. As shown in Table 6, an analysis of variance (F test) was performed on the data to determine if a significant difference in the results existed from changes in humidity. Sample recoveries and OE for the three different humidity levels were also considered. The calculated F value is greater than the critical value and a significant effect from humidity appears to exist. A slight decrease in average recovery is apparent at low humidity (30% RH); however, results are still within OE limits (< ±25%) and corrective action when sampling at low humidities appears unnecessary.

  1. Conversion Factor (C.F.)

As described in OSHA Method No. ID-190 (11.1.), the proposed factor for the conversion of NO2 gas to NO2 is concentration-dependent. If the reaction is stoichiometric, a C.F. of 0.5 would be seen experimentally; however, this does not appear to occur at low concentrations. For concentrations below 10 ppm, the average C.F. is 0.6 to 0.7 [as reported by Morgan et. al. (11.9.), in a previous OSHA study (11.10.), and by numerous others (11.3.-11.5.)]. For concentrations of 0 to 10 ppm NO2, a factor of 0.63 was adopted by OSHA (11.10.) and NIOSH (11.11.). The factor was not well defined at higher concentrations and needed further evaluation.

Procedure: The following two procedures were used to experimentally determine the C.F. for concentrations greater than 10 ppm.

  1. Determination of C.F. using oxidation of NO
    1. The same generation system shown in Figure 1was used. Nitrogen dioxide was produced by flowing a diluted NO mixture through SKC oxidizer sections.
    2. The generation system was set at 50% RH and 25°C.
    3. The NO2produced was then collected using impingers containing 1.5% TEA solutions. Variable time periods (30 to 360 min) and different concentration ranges were used. The TEA solutions were used in an attempt to avoid any extraneous background contribution or intrinsic contamination that is sometimes noted when using the impregnated solid sorbent. Samples were taken at a flow rate of about 0.025 L/min primarily to assure complete oxidation of the NO and secondarily to provide sufficient residence time of NO2 in the TEA solutions.
  2. Determination of C.F. using NO2permeation tubes
    1. A second study was performed using permeation tubes (Thermedics Inc., Woburn, MA) as the NO2 The system was setup as mentioned in reference 11.2.
    2. The generation system was set at 50% RH and 25°C.
    3. Samples were taken using impingers containing 1.5% TEA. Flow rates of 0.15 mL/min were used to collect samples for 30 to 60 min (Note: A higher sample flow rate was possible because NO2was used instead of NO).

Results: The results for C.F. calculations from about 1 to 193 ppm are listed in Table 7. This data shows the C.F. for the 10 to 100 ppm concentration range averaged approximately 0.50; at about 200 ppm the factor apparently decreased to 0.37. Further work may be necessary to determine why the factor decreased at the 200 ppm level. As mentioned in Section 4, no breakthrough was found on backup tubes when sampling at 200 ppm.

Proposed curve fits for the C.F. are shown in Figure 2a and Figure 2b. Figure 2b is an expanded scale version of Figure 2a. As a comparison with other authors experiments, some of the data (<15 ppm NO2) used in the curve fit were taken from the following studies found in literature:

NO2 ppm C.F. Literature Source (reference no.)
0.01 1* 11.13., 11.14.
3.4 0.73 11.4., 11.5.
9.05 0.61 11.4., 11.5.
10.7 0.56 11.4., 11.5.
* The first data set (0.01, 1) is used to force a value of unity for a concentration well below the limit of detection. The C.F. value of unity was determined only for a passive monitor (11.13., 11.14.) where the NO2 concentration at the monitor face is apparently very low (11.13.).

The conversion factor appears to follow either general curve fit:

Y = (a) x (NO)b (1)
or
Y = (a) + (b) × ln(NO) (2)

where:

Y = calculated C.F.
NO = uncorrected ppm NO
a = slope; for equation (1), a = 0.7140, for (2), a = 0.7372
b = intercept; for equation (1), b = -0.09714, for (2), b = -0.06368

The standard deviation about the regression line (Sy/X) for (1) was 0.0536 and 0.0393 for equation (2).

According to the reaction proposed by Gold (11.4.), NO2 and triethanolammonium nitrate are formed in the reaction of NO2 with TEA. The amount of nitrate (NO3) produced has not been documented at different NO2 concentrations. As can be seen by Figure 2a and Figure 2b, as the concentration of NO2 (or NO) decreases, the subsequent formation of NO2 (in relation to NO2) increases. As the NO2 concentration decreases, theoretically the NO3 concentration should also decrease. although bubblers with TEA solutions were used at one point in the experiment in an attempt to rule out NO3 contamination, the NO3 concentrations could not be confirmed due to the apparent contamination of NO3 found in the generation system and sorbent material. The measured concentration of NO3 did not appear to change in relation to NO2 concentration. Comparison of the ratios of peak areas for the two analytes (NO2/NO3) across the concentration range tested gave variable, almost random results. When considering NO2 concentrations below 25 ppm, this ratio would be expected to increase as the concentration of NO2decreases.

The correction for the conversion of NO2 to NO2 has been approximated using an average C.F. of 0.63 for less than 10 ppm NO (or NO2) and 0.50 for concentrations above 10 ppm. A computer simulation using the approximate 0.63 and 0.5 C.F. values for a concentration range of 1 to 100 ppm gave results within +11% of those calculated using equation (1). The approximate C.F.s were within +5% of the calculated factors for most of the concentration range. The greatest disagreement between calculated and approximate C.F.s occurs at about 10 ppm.

The two approximate C.F. values were used for all data contained in this backup report and were recommended in the method (11.1.). These two C.F. values appeared to be more convenient to use and the potential difference between calculated and approximate C.F. values in the concentration range tested is minor.

Further work to accumulate a larger data base of C.F. values and consequently more accurate slope and intercept values should be performed before extensive use of these equations (especially below 1 ppm NO2). This work may also reveal whether one equation is more suitable to use. Also, a more controlled study of the NO3 concentration and contamination may shed light on the reaction mechanism at low concentrations.

  1. Sampling and Analysis of a Mixture of NO and NO2

Procedure: A determination of the ability of the three-tube sampling device to sample NO/NO2 mixtures was assessed. A mixture of NO and NO2 was generated using equipment described in the Introduction (for NO) and as mentioned in reference 11.2. (for NO2). Samples were taken using the sampling device for 1 h at a flow rate of 0.15 L/min (50% RH and 25°C).

Results: Results are shown in Table 8. The mixture study indicates the sampling tube is capable of collecting a mixture of NO and NO2 at their respective PEL concentrations for 1 h.

  1. Sampling and Analysis – Supelco Tubes

Procedure: A preliminary evaluation of the combination device manufactured by Supelco was conducted using the same conditions and equipment mentioned in the Introduction. Samples were collected using the procedure mentioned in Section 2. Two sets of six samples were taken at the PEL and 50% RH. A sampling flow rate of about 0.025 L/min and a sampling time of 4 h was used.

Results: Results are listed in Table 9. The Supelco tube results indicate extremely variable and mainly low recoveries when sampling at the PEL. The oxidizer in the Supelco tube contained only about 800 mg and may have contributed to the low recovery by not having sufficient oxidizing power to convert all of the NO to NO2. Preliminary tests conducted by NIOSH (11.12., 11.15.) indicated 800 mg of oxidizer gave significantly lower recoveries for NO concentrations greater than 12 ppm. The SKC tubes tested for this evaluation (Method No. ID-190) contained approximately 1 g oxidizer per tube.

  1. Discussion

The data generated during the validation indicate this method is an acceptable alternative to the polarographic method. The ion chromatographic method offers an accurate and precise determination of compliance with the OSHA 25 ppm TWA PEL for NO. A concentration-dependent conversion factor is required in calculations. although data was not presented in this backup report regarding sorbent contamination, previous studies have indicated serious contamination problems (11.2., 11.16.). The molecular sieve solid sorbent must be washed with deionized water before impregnation and tube packing. This water washing will remove any soluble contaminants such as chloride or nitrite salts present in the molecular sieve. An attempt to identify the NO2-TEA reaction products has been performed (11.17.); however, future work needs to be conducted to further identify and characterize the mechanism and conversion factors of this reaction.

  1. References
    1. Occupational Safety and Health Administration Technical Center:Nitric Oxide in Workplace Atmospheres by J.C. Ku (USDOL/ OSHA-SLTC Method No. ID-190). Salt Lake City, UT. Revised 1991.
    2. Occupational Safety and Health Administration Technical Center:Nitrogen Dioxide Backup Data Report (ID-182), by J.C. Ku. Salt Lake City, UT. Revised 1991.
    3. Saltzman, B.E.:Colorimetric Microdetermination of Nitrogen Dioxide in the Atmosphere.  Chem.26:1949 (1954).
    4. Gold, A.:Stoichiometry of Nitrogen Dioxide Determination in Triethanolamine Trapping Solution.  Chem.49:1448-1450 (1977).
    5. Blacker, J.H.:Triethanolamine for Collecting Nitrogen Dioxide in the TLV Range.  Ind. Hyg. Assoc. J.34:390 (1973).
    6. Occupational Safety and Health Administration Analytical Laboratory:Precision and Accuracy Data Protocol for Laboratory Validations. In OSHA Analytical Methods Manual. Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.
    7. National Institute for Occupational Safety and Health:Documentation of the NIOSH Validation Testsby D. Taylor (DHEW/NIOSH Pub. No. 77-185). Cincinnati, OH, 1977.
    8. Mandel, J.:Accuracy and Precision, Evaluation and Interpretation of Analytical Results, The Treatment of Outliers. In Treatise on Analytical Chemistry. 2nd ed. edited by Kolthoff, I.M. and P.J. Elving. New York: John Wiley and Sons, Inc., 1978. p 282.
    9. Morgan, G.B., C. Golden, and E.C. Tabor:“New and Improved Procedures for Gas Sampling and Analysis in the National Air Sampling Network” Paper presented at the 59th Annual Meeting of the Air Pollution Control Association, San Francisco, CA, 1966.
  • Occupational Safety and Health Administration Analytical Laboratory:OSHA Analytical Methods Manual(USDOL/OSHA-SLCAL Method No. ID-109). Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.
  • National Institute for Occupational Safety and Health:NIOSH Manual of Analytical Methods, 2nd ed., Vol. 4 (DHEW/NIOSH Pub. No. 78-175, Method No. S321). Cincinnati, OH, 1978.
  • Willey, M.A., C.S. McCammon, Jr., and L.J. Doemeny:A Solid Sorbent Personal Sampling Method for the Simultaneous Collection of Nitrogen Dioxide and Nitric Oxide in Air.  Ind. Hyg. Assoc. J.38:358-363 (1977).
  • Palmes, E.D., A.F. Gunnison, J. DiMattio and C. Tomczyk:Personal Sampler for Nox Ind. Hyg. Assoc. J.37:570-577 (1976).
  • National Institute for Occupational Safety and Health:NIOSH Manual of Analytical Methods, 3rd ed. (Method 6700) edited by P.M. Eller (DHHS/NIOSH Pub. 84-100), Washington, D.C.: Government Printing Office, 1984.
  • Jones, V., and T.A. Ridjik:Nitric oxide oxidation method for field calibration of nitrogen dioxide meters.  Ind. Hyg. Assoc. J.41:433-436 (1980).
  • Occupational Safety and Health Administration Analytic Laboratory:Special Project – Evaluation of TEA Tubes for Contamination. by D.C. Cook. Salt Lake City, UT. 1985 (unpublished).
  • Aoyama, T., Yashiro, T.:Investigation of the reaction by trapping nitrogen dioxide in air using the triethanolamine method.  Chromatogr.<em265< em=””>:69-78 (1983).</em265<>

 

Table 1
Analysis – Nitric Oxide

µg* Taken µg* Found F/T N Mean Std Dev CV AE
(0.5 × PEL)
103.04
103.04
103.04
103.04
103.04
103.04
105.19
110.45
105.26
117.47
113.68
111.08
1.0209
1.0719
1.0215
1.1400
1.1033
1.0780
6 1.073 0.046 0.043 15.9
(1 × PEL)
206.09
206.09
206.09
206.09
206.09
206.09
226.24
239.92
226.80
241.83
215.14
210.37
1.0978
1.1642
1.1005
1.1734
1.0439
1.0208
6 1.100 0.062 0.056 21.2
(2 × PEL)
412.17
412.17
412.17
412.17
412.17
412.17
415.69
447.42
422.43
429.73
448.54
424.95
1.0085
1.0855
1.0249
1.0426
1.0882
1.0310
6 1.047 0.033 0.031 11.0
* Results are listed as micrograms nitric oxide. These values already have the Conversion Factor applied.
F/T = Found/Taken = Desorption Efficiency
AE = Analytical Error (±%)
Bias = +0.073
CV1 (Pooled) =   0.045
Analytical Error (Total) = ±16.3%

Table 2
Sampling and Analysis – Nitric Oxide

ppm* Taken ppm* Found F/T N Mean Std Dev CV OE
(0.5 × PEL)
13.04
13.04
13.04
13.04
13.04
13.04
13.04
10.70
12.57
12.55
12.58
13.77
14.87
14.17
0.8206
0.9640
0.9624
1.0560
1.1403
1.0867
7 0.999 0.105 0.105 21.1
(1 × PEL)
25.93
25.93
25.93
25.93
25.93
25.93
27.04
26.51
26.23
28.99
28.92
29.55
1.0428
1.0224
1.0116
1.1180
1.1153
1.1396
6 1.075 0.056 0.052 17.8
(2 × PEL)
50.52
50.52
50.52
50.52
50.52
50.52
50.52
54.02
48.50
48.77
48.29
57.02
55.49
52.87
1.0693
0.9600
0.9654
0.9559
1.1287
1.0984
1.0465
7 1.032 0.072 0.069 17.1
* Results are listed as ppm nitric oxide
F/T = Found/Taken
OE = Overall Error (±%)
Bias = +0.033
CV2 (Pooled) =   0.080
CVT (Pooled) =   0.082
Overall Error (Total) = ±19.7%

Table 3
Collection Efficiency – Nitric Oxide
(25°C and 50% RH)

———-µg NO Found in———-
Sample No. First Tube Second Tube % Collection Efficiency
1
2
3
4
5
6
7
277.95
215.05
254.07
258.54
292.02
279.74
265.27
ND
ND
ND
ND
ND
ND
ND
100
100
100
100
100
100
100
Note: (1) Sampling rate approximately 0.025 L/min at approximately 2 times the PEL for 240 min
(2) ND = None detectable <2.3 µg NO2 (10-mL sample volume)

Table 4
Breakthrough Study – Nitric Oxide
(25°C, 30% RH)

———-µg NO Found in———-
Time, Min n First Tube Second Tube % Breakthrough
60
120
180
240
3
3
3
3
291.18
657.64
960.63
1,074.23
ND
ND
ND
ND
0
0
0
0
Note: (1) Sampled at approximately 0.025 L/min flow rate – pump flow rates were slightly different from sample to sample
(2) Generation concentration = 200 ppm NO
(3) n = number of samples
(4) ND = None detectable <2.3 µg NO2 (10-mL sample volume)

Table 5
Storage Stability
* – Nitric Oxide

Storage Day Found µg Air Vol (L) Found ppm Taken ppm % Recovery
Day 1 361.30
358.45
374.25
6.45
6.37
6.66
29.77
29.91
29.87
28.45
28.45
28.45
104.6
105.1
105.0
           n
Mean
Std Dev
CV
3
104.9
0.26
0.0025
Day 3 345.52
348.59
345.59
6.58
6.45
6.66
27.91
28.72
27.59
28.66
28.66
28.66
97.4
100.2
96.3
           n
Mean
Std Dev
CV
3
98.0
2.0
0.021
Day 15 370.67
339.51
331.44
6.60
6.31
6.66
29.85
28.60
26.45
28.66
28.66
28.66
104.2
99.8
92.3
           n
Mean
Std Dev
CV
3
98.8
6.01
0.061
Day 30 362.52
366.26
353.78
6.59
6.40
6.72
29.24
30.42
27.98
28.51
28.51
28.51
102.6
106.7
98.1
           n
Mean
Std Dev
CV
3
102.4
4.30
0.042
* SKC sampling devices, Lot No. 444 were used

 

Table 6
Humidity Test (25°C) – Nitric Oxide

% RH 30 50 80
NO Found, ppm 22.94
23.51
22.60
22.67
26.11
24.87
25.18
27.04
26.51
26.23
28.99
28.92
29.55
26.73
26.54
25.49
25.70
31.13
27.81
n
Mean, ppm
Std Dev, ppm
CV
Known Conc., ppm
Recovery, %
7
23.98
1.40
0.058
26.17
91.6
6
27.87
1.44
0.052
25.93
107.5
6
27.23
2.08
0.076
25.78
105.6
F test results:
Fcalc = 10.5
Fcrit  = 6.23     p <0.01     df = 2, 16

 

Table 7
Nitrogen Dioxide Conversion Factor

NO2 ppm* n Std Dev CV Average C.F.** Source
0.82
12.89
13.72
15.74
19.85
25.20
39.65
49.79
77.85
97.90
158.57
192.57
4
7
5
5
4
7
5
6
5
6
5
7
0.082
0.038
0.023
0.037
0.032
0.037
0.031
0.022
0.024
0.020
0.018
0.025
0.150
0.074
0.041
0.072
0.063
0.070
0.058
0.043
0.050
0.044
0.042
0.068
0.817
0.519
0.569
0.513
0.509
0.533
0.529
0.517
0.480
0.450
0.437
0.368
1
1
1
2
2
1
2
1
2
1
2
1
* NO2 ppm <=> NO ppmn = number of samples – collection media for all samples was 1.5% TEA solution** Average C.F. (conversion factor) was calculated from sample results assuming 100% recoverySource 1 = NO cylinder + oxidizersSource 2 = NO2 permeation tubes

Table 8
Nitrogen Dioxide – Nitric Oxide Mixture Study
(25°C & 50% RH)

Nitrogen Dioxide Nitric Oxid
Air Vol, L Found ppm Taken ppm Found ppm Taken ppm
7.61
8.14
9.16
7.61
8.14
9.16
5.38
5.34
5.52
5.25
6.48
4.82
5.24
5.24
5.24
5.24
5.24
5.24
25.91
26.24
28.23
25.26
34.74
23.26
28.76
28.76
28.76
28.76
28.76
28.76
                 n
Mean
Std Dev
CV
Recovery
         6
5.47
0.55
0.101
104.4%
      6
27.27
3.99
0.146
94.8%

Table 9
Preliminary Sampling & Analysis – Nitric Oxide
Supelco Tubes

 

 

ppm* Taken

ppm* Found F/T N Mean Std Dev CV OE
(1 × PEL Set 1)
25.96
25.96
25.96
25.96
25.96
25.96
25.96
6.07
20.14
22.02
20.42
9.99
26.62
10.52
0.234
0.776
0.848
0.787
0.385
1.025
0.405
7 0.637 0.294 0.461 128.
(1 × PEL Set 2)
26.08
26.08
26.08
26.08
26.08
26.08
26.08
13.22
22.34
9.63
22.47
4.88
8.46
9.19
0.507
0.857
0.369
0.862
0.187
0.324
0.352
7 0.494 0.266 0.539 158.
* Results are listed as ppm nitric oxide
F/T = Found/Taken
OE = Overall Error (±%)
Supelco tubes, lot no. 564-07, were used.

Generation System

A block diagram of the major components of the dynamic generation system is shown below. The system consists of four essential elements, a flow, temperature and humidity control system, a nitric oxide vapor generating system, a mixing chamber and an active sampling manifold.

Figure 1

Figure 1

Proposed Conversion Factor Fits

Figure 2a

Solid Line
Broken Line
y = (a) + (b) × ln(X)
y = (a) × (X)b
See Section 7 of the text for further descriptions

Figure 2a

Proposed Conversion Factor Fits

Figure 2b

Solid Line
Broken Line
y = (a) + (b) × ln(X)
y = (a) × (X)b
See Section 7 of the text for further descriptions

Figure 2b

Nguồn: https://www.osha.gov

Nitric oxide (NO) – Giới thiệu vai trò và tác động môi trường

Nitric oxide (NO), colourless, toxic gas that is formed by the oxidation of nitrogen. Though it has few industrial applications, nitric oxide performs important chemical signaling functions in humans and other animals and has various applications in medicine. It is also a serious air pollutant generated by automotive engines and thermal power plants.

Nitric oxide is formed from nitrogen and oxygen by the action of electric sparks or high temperatures or, more conveniently, by the action of dilute nitric acid upon copper or mercury. It was first prepared about 1620 by the Belgian scientist Jan Baptist van Helmont, and it was first studied in 1772 by the English chemist Joseph Priestley, who called it “nitrous air.”

Nitric oxide liquefies at −151.8 °C (−241.2 °F) and solidifies at −163.6 °C (−262.5 °F); both the liquid and the solid are blue in colour. The gas is almost insoluble in water, but it dissolves rapidly in a slightly alkaline solution of sodium sulfite, forming the compound sodium dinitrososulfite, Na2(NO)2SO3. It reacts rapidly with oxygen to form nitrogen dioxide, NO2. Nitric oxide is a relatively unstable, diatomic molecule that possesses a free radical (i.e., an unpaired electron). The molecule can gain or lose one electron to form the ions NO− or NO+.

In the chemical industry, nitric oxide is an intermediate compound formed during the oxidation of ammonia to nitric acid. An industrial procedure for the manufacture of hydroxylamine is based on the reaction of nitric oxide with hydrogen in the presence of a catalyst. The formation of nitric oxide from nitric acid and mercury is applied in a volumetric method of analysis for nitric acid or its salts.

Though it is a toxic gas at high concentrations, nitric oxide functions as an important signaling molecule in animals. It acts as a messenger molecule, transmitting signals to cells in the cardiovascular, nervous, and immune systems. It is the only gas that is known to act as a messenger molecule within the human body. The nitric oxide molecule’s possession of a free radical makes it much more reactive than other signaling molecules, and its small size enables it to diffuse through cell membranes and walls to perform a range of signaling functions in various bodily systems. The body synthesizes nitric oxide from the amino acid L-arginine by means of the enzyme nitric oxide synthase.

The main site of the molecule’s synthesis is the inner layer of blood vessels, the endothelium, though the molecule is also produced by other types of cells. From the endothelium, nitric oxide diffuses to underlying smooth muscle cells and causes them to relax. This relaxation causes the walls of blood vessels to dilate, or widen, which in turn increases blood flow through the vessels and decreases blood pressure. Nitric oxide’s role in dilating blood vessels makes it an important controller of blood pressure. Nitric oxide is also produced by neurons (nerve cells) and is used by the nervous system as a neurotransmitter to regulate functions ranging from digestion to blood flow to memory and vision. In the immune system, nitric oxide is produced by macrophages, which are a type of leukocyte (white blood cell) that engulf bacteria and other foreign particles that have invaded the body. The nitric oxide released by macrophages kills bacteria, other parasites, and tumour cells by disrupting their metabolism.

Nitric oxide’s role in regulating blood flow and pressure is utilized by modern medicine in several ways. The drug nitroglycerin has been used since the late 19th century to relieve the condition known as angina pectoris, which is caused by an insufficient supply of blood to the heart muscle. Nitroglycerin was long known to achieve its therapeutic effect by dilating the coronary arteries (thereby increasing the flow of blood to the heart), but why it did so remained unknown until the late 1980s, when researchers realized that the drug serves to replenish the body’s supply of nitric oxide, more of which is then available to relax, and thereby widen, the coronary blood vessels.

Another medical use of nitric oxide is in the treatment of impotence, or erectile dysfunction, in men. Nitric oxide is essential to the achievement of an erection. During sexual stimulation, nitric oxide released within the penis relaxes the smooth muscle cells of the corpus cavernosa, making it easier for blood to flow into those spongy tissues, the expansion of which hardens and elevates the penis. The drug sildenafil citrate (trade name Viagra) treats impotence by enhancing nitric oxide’s relaxant effects on smooth muscle cells in the corpus cavernosa, resulting in the increased blood flow that causes an erection.

Nitric oxide is an important component of the air pollution generated by automotive engines and thermal power-generating plants. When a mixture of air and hydrocarbon fuel is burned in an internal-combustion engine and a power plant, the ordinarily inert nitrogen in the air combines with oxygen at very high temperatures to form nitric oxide. The nitric oxide and hydrocarbon vapours emitted by automotive exhausts and power-plant smokestacks undergo complex photochemical reactions in the lower atmosphere to form various secondary pollutants called photochemical oxidants, which make up the photochemical smog that hovers over many large cities. Nitric oxide combines with water vapour in the atmosphere to form nitric acid, which is one of the components of acid rain. Heightened levels of atmospheric nitric oxide resulting from industrial activity may also be one of the causes of the gradual depletion of the ozone layer in the upper atmosphere. Sunlight causes nitric oxide to react chemically with ozone (O3), thereby converting the ozone to molecular oxygen (O2).

Nguồn: https://www.britannica.com

Sulfur Dioxide (SO2) – Lấy mẫy và phương pháp phân tích (bài 2)

Nguồn: https://www.osha.gov

Method Number: ID-104
Matrix: Air
OSHA Permissible Exposure Limits
Sulfur Dioxide (Final Rule Limit):
2 ppm (Time Weighted Average)
5 ppm (Short-Term Exposure Limit)

Sulfur Dioxide (Transitional Limit):

5 ppm (Time Weighted Average)
Collection Device: A calibrated personal sampling pump is used to draw a known volume of air through a midget-fritted glass bubbler containing 10 to 15 mL of 0.3 N hydrogen peroxide.
Recommended Air Volume: 15 to 60 L
Recommended Sampling Rate: 1 L/min
Analytical Procedure: Samples are directly analyzed with no sample preparation by ion chromatography as total sulfate.
Detection Limits
Qualitative:
0.0041 ppm (60-L air volume)

Quantitative:

0.010 ppm (60-L air volume)
Precision and Accuracy
Validation Level:
2.5 to 10.0 ppm (60-L air volume)

CVT:

0.012

Bias:

-0.046

Overall Error:

±7%
Classification: Validated Method
Chemists: Ted Wilczek, Edward Zimowski
Date (Date Revised): 1981 (December, 1989)

Commercial manufacturers and products mentioned in this method are for descriptive use only and do not constitute endorsements by USDOL-OSHA. Similar products from other sources can be substituted.


Branch of Inorganic Methods Development
OSHA Technical Center
Salt Lake City, Utah

  1. IntroductionThis method describes the collection and analysis of airborne sulfur dioxide (SO2) using midget-fritted glass bubblers (MFGBs) in the workplace. It is applicable for both short-term (STEL) and time weighted average (TWA) exposure evaluations.
    1. HistoryAn earlier method used by OSHA involved collecting SO2 in 0.3 N hydrogen peroxide (H2O2) which converted SO2 to sulfuric acid. The amount of SO2 in the air is determined in the laboratory by volumetric titration of the sulfuric acid with barium perchlorate and a Thorin indicator (8.1.). The titration is susceptible to interferences from volatile phosphates and metals (8.1.), and the end point is difficult to determine. Also, a report indicated the chloride ion has an adverse effect on the endpoint (8.2.). Method no. ID-104 has replaced the titration with ion chromatography (IC). A method using a solid sorbent sampling media and analysis by IC was recently evaluated (8.3.); however, the sorbent material appears prone to contamination.
    2. PrincipleSulfur dioxide is collected in a MFGB containing 0.3 N H2O2. The H2O2 converts the SO 2 to sulfuric acid (H2SO4) according to the following equation:

      SO2 + H2O2 ———> H2SO4

      The H2SO4 is analyzed as sulfate using a slightly basic eluent and an ion chromatograph equipped with a conductivity detector.

    3. Advantages and Disadvantages
      1. This method has adequate sensitivity for measuring workplace atmosphere concentrations of SO2 and is less affected by interferences found in the barium perchlorate titration method.
      2. The method can be fully automated to improve analytical precision.
      3. Collected samples are analyzed by means of a quick instrumental method, since no sample preparation is required.
      4. Humidity does not affect the collection efficiency.
      5. The sulfuric acid formed is stable and non-volatile.
      6. A disadvantage is the sampling device. The use of bubbler collection techniques may impose inconveniences for industrial hygiene work. There is the possibility of spillage during sampling, handling, and during transportation to the lab.
    4. Potential sources of occupational exposure to SO2 (8.4., 8.5.) Sulfur dioxide is used in industry as a(n):
      • intermediate in the manufacture of sulfuric acid
      • bleaching agent
      • disinfectant
      • fumigant
      • solvent
      • refrigerant
      • food preservative
      • reagent in the manufacture of magnesium, sodium sulfite, and other chemicals.

      Sulfur dioxide is also an industrial by-product and can be generated from many industrial processes. These include the smelting of sulfide ores, the combustion of coal or fuel oils containing sulfur as an impurity, paper manufacturing, and petroleum refining (8.4.).

    5. Physical Properties: Sulfur dioxide (CAS No. 7446-09-5) is a colorless, nonflammable gas with a characteristic, strong and suffocating odor. It is intensely irritating to the eyes and respiratory tract. It is soluble in water, methane, ethanol, chloroform, ethyl ether, acetic acid, and sulfuric acid (8.4., 8.5.).
      Physical Constants
      Chemical Formula: SO2
      Formula Weight: 64.07
      Boiling Point: -10.0°C
      Melting Point: -72.7°C
      Vapor Density:

      2.3 (air = 1)

  2. Range and Detection Limit (8.6.)This method was evaluated over the range of 2.5 to 10.0 ppm (atmospheric conditions of 640 mmHg and 24°C). Total air sample volumes of 60 L were used. The analytical portion of the evaluation was conducted using a model 10 ion chromatograph with a 3 x 500-mm separator and 6 x 250-mm suppressor columns. The following results were obtained using this equipment.
    1. The sensitivity of the method for the instrumentation used during the validation study was 1.5 microsiemens/cm/µg as sulfate ion. A 100 µL injection of a 10 µg/mL solution of sulfate gave a 27-mm chart deflection on a 500-mV chart recorder. The ion chromatograph was set on a range of 30 microsiemens/cm.
    2. The qualitative detection limit of the analytical method was 0.013 µg of SO2 per injection (200-µL sample injection) or 0.65 µg SO2 in a 10-mL sample volume.
    3. The quantitative limit was 0.033 µg SO2 per 200-µL injection or 1.7 µg SO2 in a 10-mL sample volume. The coefficient of variation of replicate determinations of standards at this level was less than 0.10.
  3. Method Performance (8.6.)This method was evaluated in 1981 using commercial analytical equipment mentioned in Section 2.Advances in ion chromatographic and sampling instruments should enable users to obtain similar or better results than those mentioned below.
    1. The coefficient of variation (CVT) for the overall sampling and analytical method in the range of 2.5 to 10 ppm (640 mmHg and 24°C) was 0.012.
    2. In validation experiments, this method was capable of measuring within ±25% of the true value (95% confidence level) over the validation range. The bias was -0.046 and overall error was ±7%.
    3. The collection efficiency was 100% for the 0.3 N H202 sampling solution.
    4. A breakthrough test was conducted at a concentration of 9.4 ppm. No breakthrough occurred after 240 min at a sampling rate of 1 L/min.
    5. In storage stability studies, the average recovery of samples analyzed after 31 days were within 1% of the average recovery of samples analyzed immediately after collection.
  4. Interferences
    1. The presence of other particulate sulfate compounds and sulfuric acid in the air will interfere in the analysis of sulfur dioxide. These two interferences can be removed by the use of a modified prefilter.
    2. Sulfur trioxide gas (SO3), if present in a dry atmosphere, can give a positive bias in the SO2 determination.
    3. Any substance that has the same retention time as the sulfate ion with the ion chromatographic operating conditions as described in this method is an interference. If the possibility of an interference exists, changing the separation conditions (column length, eluent flow rate and strength, etc.) may circumvent the problem.
    4. When other substances are known or suspected to be present in the air sampled, the identities of the substances should be transmitted with the sample.
  5. Sampling
    1. Equipment
      1. Hydrogen peroxide (30% H2O2), reagent grade or better.
      2. Collection solution, 0.3 N H2O2. Carefully dilute 17 mL of 30% H2O2 solution to 1 L with deionized water.
      3. Personal sampling pumps capable of sampling within ±5% of the recommended flow rate of 1 L/min are used.
      4. Midget-fritted glass bubblers (MFGBs), 25-mL, part no. 7532 (Ace Glass Co., Vineland, NJ).
      5. Shipping vials: Scintillation vials, 20-mL, part no. 74515 or 58515, (Kimble, Div. of Owens-Illinois Inc., Toledo, OH) with polypropylene or Teflon cap liners. Tin or other metal cap liners should not be used.
      6. A stopwatch and bubble tube or meter are used to calibrate pumps.
      7. Various lengths of polyvinyl chloride (PVC) tubing are used to connect bubblers to the pumps.
      8. If particulate sulfate or sulfuric acid is suspected to also be in the atmosphere, a modified prefilter assembly is used. This assembly consists of:
        • 1. Sampling cassettes, polystyrene, 37-mm.
        • 2. Mixed-cellulose ester (MCE) filters, 37 mm.
        • 3. Support rings, cellulose, part no. 225-23 (SKC Inc., Eighty Four, PA). Rings can also be made from 37-mm cellulose backup pads – Place a half-dollar in the center of the pad and then cut the outer ring formed. Place this ring in the cassette to provide support for the MCE filter.
    2. Sampling procedure
      1. Calibrate the sampling pump with a MFGB containing about 10 to 15 mL of collection solution in-line.
      2. Place 10 to 15 mL of collection solution in an MFGB. Connect the MFGB to a calibrated sampling pump and then place the sampling device in the breathing zone of the employee.
      3. If particulate sulfate or sulfuric acid are suspected to be present, attach the modified prefilter (Section 5.1.8.) to the MFGB with PVC tubing so that sampled air enters the cassette first. Minimize the amount of tubing from the filter to the MFGB.
      4. Sample at a flow rate of 1 L/min. For STEL determinations, sample for at least 15 min. For measurements of TWA exposures, sample from 60 to 240 min. Take enough samples to cover the shift worked by the employee.
      5. Transfer the collection solution into a 20-mL glass scintillation vial. Rinse the bubbler with 2 to 3 mL of unused collection solution and transfer the rinsings into the sample vial. Place the Teflon- or polypropylene-lined cap tightly on each vial and seal with vinyl or waterproof tape around the caps to prevent leakage during shipment.
      6. Prepare blank solutions by taking 10 to 15 mL of the unused collection solution and transfer to individual 20-mL glass vials. Seal vials as mentioned in Section 5.2.5.
      7. Request sulfur dioxide analysis on the OSHA 91A form. If sulfuric acid is also suspected in the sampled atmosphere and a prefilter assembly was used, the MCE filter can be submitted for sulfuric acid analysis.
      8. Ship the samples to the laboratory using appropriate packing materials to prevent breakage.
  6. Analysis
    1. Precautions
      1. Refer to instrument and standard operating procedure (SOP) manuals (8.7.) for proper operation.
      2. Observe laboratory safety regulations and practices.
      3. Sulfuric acid (H2SO4) can cause severe burns. Wear protective eyewear, gloves, and labcoat when using concentrated H2SO4.
    2. Equipment
      1. Ion chromatograph (model no. 2010i or 4500, Dionex, Sunnyvale, CA) equipped with a conductivity detector.
      2. Automatic sampler (model no. AS-1, Dionex) and 0.5 mL sample vials (part no. 038011, Dionex).
      3. Laboratory automation system: Ion chromatograph interfaced to a data reduction and control system (model no. AutoIon 450, Dionex).
      4. Micromembrane suppressor (model no. AMMS-1, Dionex).
      5. Anion separator column (model no. HPIC-AS4A, Dionex) with pre-column (model no. HPIC-AG4A, Dionex).
      6. Disposable syringes (1 mL) and syringe pre-filters, 0.5 µm pore size, (part no. SLSR 025 NS, Millipore Corp., Bedford, MA).

        (Note: Some syringe pre-filters are not cation- or anion-free. Tests should be done with blank solutions first to determine suitability for the analyte being determined).


      7. Miscellaneous volumetric glassware: Micropipettes, volumetric flasks, graduated cylinders, and beakers.
      8. Analytical balance (0.01 mg).
    3. Reagents – All chemicals should be at least reagent grade.
      1. Deionized water (DI H2O) with a specific conductance of less than 10 microsiemens.
      2. Eluent [0.0015 M sodium carbonate (Na2CO3)/0.0015 M sodium bicarbonate (NaHCO3)]: Dissolve 0.636 g Na2CO3 and 0.504 g NaHCO3 in 4.0 liters of DI H2O.
      3. Sulfuric acid (H2SO4), concentrated (98%).
      4. Regeneration solution (0.02 N H2SO4): Pipet 1.14 mL concentrated H2SO4 into a 2-L volumetric flask which contains about 500 mL DI H2O. Dilute to volume with DI H2O.
      5. Sodium sulfate (Na2SO4).
      6. Sulfate stock standard (1,000 µg/mL sulfate): Dissolve and dilute 1.4792 g Na2SO4 to 1-L with DI H2O.
    4. Standard PreparationWorking standards (100, 10, 1.0, and 0.1 µg/mL as sulfate). Make appropriate serial dilutions of the sulfate stock standard with eluent. Prepare these solutions monthly.
    5. Sample Preparation
      1. Measure and record the total solution volume of each sample with a graduated cylinder.
      2. If the sample solutions contain suspended particulate, remove the particles using a pre-filter and syringe (Note: Some pre-filters are not cation or anion free. Tests should be done with blank solutions first to determine suitability of the filter for the analyte being determined).
      3. Fill the 0.5-mL automatic sampler vials with sample solutions and push a filtercap into each vial. Label the vials.
      4. Load the automatic sampler with labeled samples, standards and blanks.
    6. AnalysisSet up the ion chromatograph and analyze the samples and standards in accordance with the SOP (8.7.). Typical operating conditions for a Dionex 2010i with a data reduction system are listed below.
      Ion chromatograph
      Eluent: 0.0015 M Na2CO3/0.0015 M NaHCO3
      Column temperature: ambient
      Conductivity detector
      Sensitivity:
      1 to 3 microsiemens
      Micromembrane Suppressor
      Regenerant flow: 3 to 5 mL/min
      Gas pressure: 5 to 10 psi
      Pump
      Pump pressure: approximately 1,000 psi
      Flow rate: 2 mL/min
      Chromatogram
      Run time: 6 min
      Sample injection loop: 50 µL
      Average retention time
      Sulfate:
      approximately 5.4 min

      Analyze a standard in the concentration range of the samples after every fourth or fifth sample and at the end of the analysis.

  7. Calculations
    1. Hard copies of chromatograms containing peak area and height data should be obtained from a printer. A typical chromatogram is shown in Figure 1.
    2. Using a least squares regression program, prepare a concentration-response curve by plotting the concentration of the prepared µg/mL values of the standards (or µg/sample if the same injection and solution volumes are used for samples and standards) versus peak areas or peak heights. Calculate sample concentrations from the curve and blank correct all samples as shown:

      C µg SO4 = (S µg/mL)(SSV) – (BL µg/mL)(BLSV)

      Where:

      C µg SO4 = Corrected amount (µg) in the sample solution.
      S µg/mL = µg/mL sample (from curve)
      SSV = Sample solution volume (from Section 6.5.1.)
      BL µg/mL = µg/mL blank (from curve)
      BLSV = Blank solution volume (from Section 6.5.1.)
    3. The concentration of SO2 in each air sample is expressed in ppm and is calculated as:

      ppm SO2 =

      MV x C µg SO4 x Conversion


      formula weight x air volume

      Where:

      MV (Molar Volume) = 24.45 (@ 25°C and 760 mmHg)
      C µg SO4 = blank corrected sample result
      Gravimetric conversion
      (SO4 to SO2)
      = 0.667
      Formula Weight (SO2) = 64.07
      Air Volume = Air sample taken (in L)

      This equation reduces to:

      ppm SO2 =

      0.2545 x C µg SO4


      air volume

    4. Reporting ResultsResults are reported to the industrial hygienist as ppm sulfur dioxide.
  8. References
    1. National Institute for Occupational Safety and Health: NIOSH Manual of Analytical Methods. 2nd. ed., Vol. 4 (Method No. S308) (DHEW/NIOSH Pub. No. 78-175). Cincinnati, OH: National Institute for Occupational Safety and Health, 1978.
    2. Steiber, R. and R. Merrill: Application of Ion Chromatography to the Analysis of Source Assessment Samples. In Ion Chromatographic Analysis of Environmental Pollutants (Volume 2), edited by J.D. Mulik & E. Sawicki. Ann Arbor, MI: Ann Arbor Science Publishers Inc., 1979. pp. 99-113.
    3. Occupational Safety and Health Administration Analytical Laboratory: OSHA Analytical Methods Manual (USDOL/OSHA-SLCAL Method No. ID-107). Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.
    4. National Institute for Occupational Safety and Health: Criteria for a Recommended Standard — Occupational Exposure to Sulfur Dioxide (DHEW/NIOSH Pub. No. 74-111). Cincinnati, OH: National Institute for Occupational Safety and Health, 1974.
    5. Fassett, D.W. and D.D. Irish, ed.: Patty’s Industrial Hygiene and Toxicology. 2nd rev. ed., Vol. 2. New York: John Wiley and Sons, 1963.
    6. Occupational Safety and Health Administration Technical Center: Sulfur Dioxide Backup Data Report (ID-104). Salt Lake City, UT. Revised, 1989.
    7. Occupational Safety and Health Administration Technical Center: Ion Chromatography Standard Operating Procedure. Salt Lake City, UT. In progress (unpublished).Chromatogram of a Mixed Standard
      Chloride 3 µg
      Nitrate 20 µg
      Phosphate 20 µg
      Sulfate 20 µg
      REPORT VOLUME DILUTION POINTS RATE START STOP

      AREA REJ

      External

      1

      1

      1863

      5Hz

      0.00

      6.21

      500000

      Pk.
      Num

      Ret
      Time

      Component
      Name

      height

      Area

      1

      0.27

      14570313

      90797038

      2

      0.85

      460000

      2628000

      3

      1.35

      chloride

      1126875

      8174000

      4

      2.47

      nitrate

      21717447

      213280000

      5

      3.98

      phosphate

      6749818

      92956000

      6

      5.37

      sulfate

      15340000

      258840000

      Figure 1

      Figure 1

Sulfur Dioxide (SO2) – Lấy mẫy và phương pháp phân tích (bài 1)

Nguồn: https://www.osha.gov

Method Number: ID-200
Matrix: Air
OSHA Permissible Exposure Limits:
Final Rule Limits:
2 ppm Time Weighted Average (TWA)
5 ppm Short-Term Exposure Limit (STEL)
    Transitional Limit: 5 ppm TWA
Collection Device: An air sample is collected using a calibrated sampling pump and a glass tube containing impregnated activated beaded carbon (IABC). A prefilter/cassette assembly can be used to collect particulate, if necessary.
Recommended Sampling Rate:
TWA & STEL:
0.1 liter per minute (L/min)
Recommended Air Volume:
TWA:
STEL:
12 L (0.1 L/min for 120 min)
1.5 L (0.1 L/min for 15 min)
Analytical Procedure: The sampling medium is desorbed in 15 mm sodium hydroxide which contains 0.3 N (approximately1%) hydrogen peroxide. An aliquot of this solution is analyzed as sulfate by ion chromatography.
Detection Limit:
Qualitative:Quantitative:
0.004 ppm (12-L air sample)
0.032 ppm (1.5-L air sample)
0.013 ppm (12-L air sample)
0.104 ppm (1.5-L air sample)
Precision and Accuracy: TWA


STEL


    Validation Range:

CVT (pooled):

Bias:

Overall Error:

1.36 to 4.16 ppm

0.048

-0.033

±12.9%

    5.79 ppm

0.028 (CV2)

+0.006

±6.2%

Method Classification: Validated Method
Chemist: James C. Ku
Date: April, 1992

 

Branch of Inorganic Methods Development
OSHA Salt Lake Technical Center
Salt Lake City, Utah

 

Commercial manufacturers and products mentioned in this method are for descriptive use only and do not constitute endorsements by USDOL-OSHA.
Similar products from other sources can be substituted.

    1. IntroductionThis method describes the sample collection and analysis of airborne sulfur dioxide (SO2). Samples are taken in the breathing zone of workplace personnel, and analysis is performed by ion chromatography (IC).1.1. HistoryPreviously, OSHA collected compliance samples for SO2 exposure determinations in midget-fritted glass bubblers containing 0.3 N (approximately1%) hydrogen peroxide (H2O2) which converted the SO2 to sulfuric acid (H2SO4). The amount of sulfate (SO42-) in the peroxide solution was measured by IC and gravimetrically converted to represent the amount of SO2 collected (5.1). Because bubblers are inconvenient to use as personal samplers due to spillage or breakage, it was desirable to develop a solid-sorbent sampling method. A method for collecting SO2 was developed, which sampled SO2 in the air using a sampling tube containing impregnated charcoal (5.2, 5.3). The chemical(s) used for charcoal impregnation were not specified and appear to be proprietary; however, the reaction implies an oxidation of SO2 using a metal hydroxide base. The impregnated charcoal oxidized SO2 to SO42-, which was then desorbed using a weakly basic solution. An aliquot of the solution was analyzed by IC (5.2, 5.3). Unfortunately, background levels of SO42- found in the impregnated charcoal were considered unacceptable, especially when applying the current Permissible Exposure Limit (PEL) of 2 ppm. Previously, the OSHA Time Weighted Average (TWA) PEL was 5 ppm SO2. Because of this contamination and the PEL reduction, OSHA reinstituted use of the bubbler method listed in reference 5.1 until better methodology could be found.Using the principle applied for the impregnated charcoal collection of SO2, a new material, impregnated activated beaded carbon (IABC) was developed. The IABC has a significantly lower background level of SO42- (< 3 µg). This current method was evaluated using the IABC as the collection media.

      1.2. Principle

      Sulfur dioxide is collected using IABC sorbent which is contained in a glass tube. The collected SO2 is converted to sulfite (SO32-) by the sorbent and then slowly oxidized to SO42-. This oxidation is augmented at the laboratory by addition of a desorbing solution containing 0.3 N (approximately1%) H2O2 in 15 mM sodium hydroxide (NaOH) to each IABC sample. The resultant SO42- is analyzed by IC using a conductivity detector; a gravimetric conversion is used to calculate the amount of SO2 collected.

      1.3. Advantages and Disadvantages

      1.3.1. This method has adequate sensitivity for determining compliance with the OSHA Short-Term Exposure Limit (STEL) of 5 ppm and the TWA-PEL of 2 ppm for workplace exposures to SO2.

      1.3.2. The method is simple, rapid, and easily automated.

      1.3.3. The SO42- contaminant (background) levels of the IABC sorbent are very low (< 3 µg), especially when compared to the impregnated charcoal previously used in OSHA Method No. ID-107.

      1.3.4. A disadvantage is the need for a desorption efficiency (DE) correction which is mass-dependent and may be lot-dependent (also see Sections 3.7.3 and 4.1).

      1.4. Method Performance

      A synopsis of method performance is presented below. Further information can be found in Section 4.

      1.4.1. This method was validated over the concentration range of 1.36 to 4.16 ppm. An air volume of 12 L and a flow rate of 0.1 L/min were used.

      1.4.2. The qualitative detection limit was 0.0187 µg/mL or 0.187 µg (as SO42-) when using a 10-mL solution volume. This corresponds to 0.004 ppm SO2 for a 12-L air volume.

      1.4.3. The quantitative detection limit was 0.0624 µg/mL or 0.624 µg (as SO42-) when using a 10-mL solution volume. This corresponds to 0.013 ppm SO2 for a 12-L air volume. A 50-µL sample loop and a detector setting of 1 microsiemens (µS) full-scale output were used.

      1.4.4. The sensitivity of the analytical method, whenusing the instrumental parameters listed in Section 3.6, was calculated from the slope of a linear working range curve (0.5 to 10 µg/mL SO42-). The sensitivity was 2.2 × 107 area units per 1 µg/mL. A Dionex Series 4500i ion chromatograph with AI450 computer software was used (Dionex, Sunnyvale, CA).

      1.4.5. This method compared favorably to OSHA Method no. ID-104 (modified) for SO2 (5.1) which served as the reference method.

      1.4.6. A desorption efficiency (DE) correction is required at mass loadings up to 400 µg SO2 (see Sections 3.7.3 and 4.1).

      1.4.7. The total pooled coefficient of variation (CVT) for samples taken at about 0.5, 1, and 2 times the OSHA PEL (1 to 4 ppm for TWA-type samples) was 0.048. The method exhibited slight negative bias (-3.3%) for this concentration range after DE corrections were applied. Other concentration range and TWA results are shown below:

      TWA STEL LOW
      CV   0.048   0.028   0.032
      Bias -3.3% +0.6% -6.5%
      OE ±12.9% ±6.2% ±12.9%

      For the STEL evaluation, 5.32 ppm was used for test atmospheres. For sampling at a concentration (LOW) near what may be expected in indoor air monitoring, approximately 0.3 ppm SO2 was used. Bias and overall error (OE) values were calculated from those found analytically versus theoretical (known) values. The theoretical concentrations were calculated from flows of a certified cylinder of SO2and dilution air.
      1.4.8. The collection efficiency at 2 times the PEL was 100%. Samples were collected from a generated test atmosphere of 4 ppm SO2for 120 min.

      1.4.9. Breakthrough tests were performed at concentrations of 7.20 and 14.8 ppm SO2. No breakthrough was found for a sampling time of 240 min and an average sample flow rate of 0.1 L/min.

      1.4.10. Samples can be stored at ambient (20 to 25 °C) temperature for a period of at least 30 days. Storage stability results show the mean sample recovery after 30 days was within ±10% of the theoretical calculations. Samples were stored on a laboratory bench.

      1.5. Interferences

      1.5.1. Other particulate sulfate compounds and H2SO4 will interfere in the analysis of SO2 if they are collected in the IABC. Particulate and H2SO4 mist can be removed from the air during sampling using a modified sampling device which contains a Teflon® pre-filter (see Section 2.1).

      1.5.2. Sulfur trioxide gas (SO3), if present in a dry atmosphere, can give a positive bias in the SO2 determination.

      1.5.3. Any substance that has the same retention time as SO42-, when using the ion chromatographic operating conditions described in this method, is an interference. If the possibility of an interference exists, changing the separation conditions (column, eluent flow rate and strength, etc.) may circumvent the problem.

      1.6. Source of Exposure

      Sulfur dioxide is generated as a by-product from many industrial processes. These include the smelting of sulfide ores, the combustion of coal or fuel oils containing sulfur as an impurity, paper manufacturing, and petroleum refining (5.4).

      1.7. Physical and Chemical Properties (5.4, 5.5)

      Sulfur dioxide (CAS No. 7446-09-5)
      Chemical formula SO2
      Formula weight   64.07
      Melting point -72.7 °C
      Boiling point -10.0 °C
      Vapor density   2.3 (air = 1)

      SO2 is a colorless, nonflammable gas with a characteristic, strong, and suffocating odor. It is soluble in water, methanol, ethanol, chloroform, ethyl ether, acetic acid, and sulfuric acid.

      1.8. Toxicology (5.6)


      Information listed within this section is a synopsis of current knowledge of the physiological effects of SO2 and is not intended to be used as a basis for OSHA policy.


      Sulfur dioxide is intensely irritating to the eyes and respiratory tract. Workplace exposure to SO2 can cause both chronic and acute effects. The chronic effects of exposure include permanent pulmonary impairment, which is caused by repeated episodes of bronchoconstriction. It has been reported that workers’ exposure to high concentrations of SO2 (80 to 100 ppm) may cause an increased incidence of nasopharyngitis, shortness of breath on exertion (dyspnea), and chronic fatigue. Concentrations of SO2 from 2 to 36 ppm produced a significantly higher frequency of respiratory disease symptoms, including chronic coughing, expectoration, and dyspnea.

      The acute effects include upper respiratory tract irritation, rhinorrhea, choking, and coughing. Within 5 to 15 minutes from the onset of exposure, workers develop temporary reflex bronchoconstriction and increased airway resistance.

    1. Sampling2.1. Equipment

      2.1.1. Calibrated personal sampling pumps capable of sampling within ±5% of the recommended flow rate of 0.1 L/min are used.

      2.1.2. Solid sorbent sampling tubes are prepared using glass tubes, glass wool plugs, and IABC.

      Sampling tubes can be commercially obtained. Two types of sampling tubes are commercially available:


      Type I  is a glass tube packed with a 100-mg IABC front and 50-mg backup section (Cat. No. 226-80, SKC Inc., Eighty Four, PA). The IABC is held in place with glass wool, foam, and a stainless steel retainer clip. If interference from particulate is probable, a prefilter/cassette sampling assembly can be used with this tube. See Section 2.1.5 for more details regarding the prefilter.


      Type II,  a combination sampling device (Forest Biomedical, Salt Lake City, UT) can be used to remove particulate and collect H2SO4 mist during SO2 sampling. The combination device, as shown below, consists of two different glass tubes connected together. The front part of the tube contains a Teflon® filter, retaining rings, foam, and a glass wool plug. The Teflon® filter is used to trap any particulate and H2SO4. The dimensions of the front portion of the sampling device are 12-mm o.d., 10-mm i.d., and 25-mm long. The second part of the device contains two sections of IABC and is used for collecting SO2. The dimensions of the second part are 6-mm o.d., 4-mm i.d., and 50-mm long. Both ends of the sampling tube are sealed with plastic caps.

      Type II - Combination Sampling Device - For problems with accessibility in using figures, illustrations and PDFs in this method, please contact the SLTC at (801) 233-4900.
      <—<—–< Sample Flow <—<—–Type II – Combination Sampling Device

      If commercial tubes are unavailable, sampling tubes can be prepared using carbon bead impregnated in the same fashion as discussed in OSHA method ID-180 for phosphine (5.7).


      Note: The grade of carbon bead appears less significant for SO2 when compared to phosphine (5.7).


      Prepare each tube for SO2 collection with a 100-mg IABC front and a 50-mg backup section. Separate each IABC section using a small amount of glass wool.

      2.1.3. A stopwatch and bubble tube or meter are used to calibrate pumps.

      2.1.4. Various lengths of polyvinyl chloride tubing are used to connect sampling tubes to pumps.

      2.1.5. If the workplace air being sampled is suspected of containing particulate which could interfere (i.e. H2SO4 or sulfates), the prefilter/cassette assembly listed below or a Type II sampling tube should be used.

      1. Filter for particulate collection, Teflon® (PTFE), 0.45 µm pore size, 25-mm diameter (part no. 130620, Nucleopore Corp., Pleasanton, CA)
      2. Carbon-filled polypropylene cassette, 25-mm diameter, (part no. 300075, Nucleopore) (See Section 4.10 for further details regarding this cassette)
      3. Porous plastic support pad (part no. 220600, Nucleopore)

      Note: Do not use glass fiber prefilters for particulate collection during sampling for SO2. Loss of SO2 can occur due to the slightly basic properties of these filters. See Section 4.10 for further details.


      Assemble the prefilter assembly such that sampled air enters the Teflon® filter first and the plastic support pad faces the sampling tube. Use a minimum amount of tubing to connect the Type I sampling tube to the prefilter assembly.

      2.2. Sampling Procedure (Bulk or wipe samples are not applicable)

      2.2.1. Connect the sampling tube (Type I or II) to the calibrated sampling pump, making sure sampled air enters the large section (100 mg) of IABC first. Place the sampling device on the employee such that air is sampled from the breathing zone.

      2.2.2. For STEL samples, use a flow rate of 0.1 L/min and a minimum sampling time of 15 min. For TWA determinations, take consecutive 12-L samples at a flow rate of 0.1 L/min for 120 min each. If possible, take enough consecutive samples to cover the entire work shift.

      2.2.3. After sampling, place plastic end caps tightly on both ends of the tube and apply OSHA Form 21 seals. Record the sampling conditions.

      2.2.4. Use the same lot of IABC tubes for blank and collected samples. Handle the blank sorbent tube in exactly the same manner as the sample tubes except that no air is drawn through it. Submit at least one blank tube for each batch of ten samples.

      2.2.5. When other compounds are known or suspected to be present in the air, such information should be transmitted with the sample.

      2.2.6. Specify SO2 analysis and ship samples to the laboratory. If necessary, any Teflon® pre-filters used can be analyzed for H2SO4(when H2SO4 is suspected to be present in the workplace atmosphere).

    1. Analysis3.1. Safety Precautions

      3.1.1. Refer to appropriate IC instrument manuals and the Standard Operating Procedure (SOP) for proper instrument operation (5.8).

      3.1.2. Observe laboratory safety regulations and practices.

      3.1.3. Sulfuric acid, sodium hydroxide, and hydrogen peroxide are corrosive. Use appropriate personal protective equipment such as safety glasses, gloves, and lab coat when handling corrosive chemicals. Prepare solutions in an exhaust hood.

      3.2. Equipment

      3.2.1. Ion chromatograph (Model 4000i or 4500i Dionex, Sunnyvale, CA) equipped with a conductivity detector.

      3.2.2. Automatic sampler (Dionex Model AS-1) and sample vials (0.5 mL).

      3.2.3. Laboratory automation system: Ion chromatograph interfaced with a data reduction system (AI450, Dionex).

      3.2.4. Micromembrane suppressor, anion (Model AMMS-1, Dionex).

      3.2.5. Separator and guard columns, anion (Model HPIC-AS4A and AG4A, Dionex).

      3.2.6. Disposable syringes (1 mL).

      3.2.7. Syringe pre-filters, 0.5-µm pore size (part no. SLSR 025 NS, Millipore Corp., Bedford, MA).


      Note: Some syringe pre-filters are not cation- or anion-free. Tests should be performed with blank solutions first to determine contamination and suitability with the analyte.


      3.2.8. Miscellaneous volumetric glassware: Micropipettes, volumetric flasks, Erlenmeyer flasks, graduated cylinders, and beakers.

      3.2.9. Scintillation vials, glass, 20-mL.

      3.2.10. Equipment for eluent degassing (vacuum pump, ultrasonic bath).

      3.2.11. Analytical balance (0.01 mg).

      3.3. Reagents – All chemicals should be at least reagent grade.

      3.3.1. Principal reagents:


      CAUTION: NaOH, H2SO4, or 30% H2O2 can cause skin irritation or burns.


      Sodium carbonate (Na2CO3)
      Sodium bicarbonate (NaHCO3)
      Sodium hydroxide (NaOH)
      Sulfuric acid (H2SO4), concentrated, 98%
      Hydrogen peroxide (H2O2), 30%
      Sodium sulfate (Na2SO4), anhydrous
      Deionized water (DI H2O) with a conductance of <10 µS.

      3.3.2. Eluent (1.0 mM Na2CO3 + 1.0 mM NaHCO3):

      Dissolve 0.212 g Na2CO3 and 0.168 g NaHCO3 in 2.0 L DI H2O, Sonicate this solution and degas under vacuum for 15 min.

      3.3.3. Suppressor regenerant solution (0.02 N H2SO4):

      Carefully transfer 1.14 mL concentrated H2SO4 into a 2-L volumetric flask which contains approximately 500 mL DI H2O. Dilute to volume with DI H2O.

      3.3.4. Desorbing solution [0.3 N (approximately1%) H2O2 in 15 mM NaOH]:

      Dissolve approximately0.6 g NaOH in approximately 500 mL of DI H2O contained in a 1-L volumetric flask. Carefully add 34 mL of 30% H2O2 and then dilute to the 1-L mark with DI H2O. Prepare weekly.

      3.3.5. Sulfate (SO42-) stock standard (1,000 µg/mL):

      Dissolve and dilute 1.4792 g of Na2SO4 to 1.0 L with DI H2O. Prepare yearly.

      3.3.6. Sulfate (SO42-) standard solutions, 100, 10, and 1 µg/mL:

      Pipette appropriate volumes of the 1,000 µg/mL SO42- stock standard into volumetric flasks and dilute to the mark with eluent. Prepare monthly.

      3.4. Working Standard Preparation

      3.4.1. Prepare SO42- working standards in eluent. A method for preparing a series of working standards using 10-mL final solution volumes is shown below:

      Working Std
      (µg/mL)


      Std Solution
      (µg/mL)


      Aliquot
      (mL)


      Eluent Added
      (mL)


        0.5
      1
      2
      5
      10
      20
      30
      50
      1
      1
      10
      10
      10
      100
      100
      100
      5
      *
      2
      5
      *
      2
      3
      5
      5
      *
      8
      5
      *
      8
      7
      5
      *Already prepared in Section 3.3.6.

      3.4.2. To prepare each working standard listed above, pipette an appropriate aliquot of the specified standard solution (prepared in Section 3.3.6) and add the specified amount of eluent.

      3.4.3. As an alternative, pipette each aliquot into a 10-mL volumetric flask and dilute to volume with eluent.

      3.5. Sample Preparation


      Note: If H2SO4 is a requested analyte and a Type II sampling device or a PTFE prefilter was used, see OSHA Stopgap Method ID-165SGor OSHA Method No. ID-113 for further details regarding sample preparation, analysis, and calculation of results for H2SO4.


      3.5.1. Carefully remove and discard the rear glass wool plug (or foam for the Type II sampler) without losing any beaded carbon.


      Note:  The sorbent should always be removed from the glass tube via the opposite end of collection (i.e. 50-mg IABC backup section is removed first). This will minimize the possibility of contamination from any collected particulate.


      3.5.2. Carefully transfer each IABC section from a sample tube and place in separate 25-mL Erlenmeyer flasks or scintillation vials.

      3.5.3. Pipette 10 mL of desorbing solution into each flask. Cap each flask tightly and allow each solution to sit for at least 60 min. Occasionally swirl each solution.

      3.6. Analysis

      3.6.1. Pipette a 0.5- to 0.6-mL portion of each standard or sample solution into separate automatic sampler vials. Place a filtercap into each vial. The large filter portion of the cap should face the solution.

      3.6.2. Load the automatic sampler with labeled samples, standards, and blanks.

      3.6.3. Set up the ion chromatograph in accordance with the SOP (5.8)


      Note: An SOP is a written procedure for a specific instrument. It is suggested that SOPs be prepared for each type of instrument used in a lab to enhance safe and effective operation.


      Typical operating conditions for a Dionex 4000i or 4500i with a conductivity detector and an automated sampler are listed below:

      Ion Chromatograph


      Eluent: 1.0 mM Na2CO3/1.0 mM NaHCO3
      Column temperature: ambient
      Anion precolumn: AG4A
      Anion separator column: AS4A
      Anion suppressor: AMMS-1
      Conductivity Output range: 1 µS
      Sample injection loop: 50 µL
      Pump


      Pump pressure: approximately900 psi
      Flow rate: 2 mL/min
      Chromatogram


      Run time: 10 min
      Peak retention time: approximately6 min for SO42-

      3.6.4. Follow the SOP for further instructions regarding analysis (5.8).

      3.7. Calculations

      3.7.1. After the analysis is completed, retrieve the peak areas or heights. Obtain hard copies of chromatograms from a printer.

      3.7.2. Prepare a concentration-response curve by plotting the peak areas or peak heights versus the concentration of the SO42-standards in µg/mL.

      3.7.3. Perform a blank correction for each IABC front and backup sections. Subtract the µg/mL SO42- blank value (if any) from each sample reading if blank and sample solution volumes are the same. If a different solution volume is used, subtract the total µg blank value from total µg sample values.

      3.7.4. Calculate the air concentration of SO2 (in ppm) for each air sample:

       A  =  (µg/mL SO42-)   ×   (Sol Vol)   ×   (GF)

      corr µg SO2  =    A


      DE

      ppm SO2  =    (corr µg SO2)   ×   (Mol Vol)


      (AV)   ×   (Mol Wt)

      Where:
      A   = uncorrected µg SO2
      corr µg SO2   = µg SO2 with DE correction applied
      µg/mL SO42-   = Amount found (from calibration curve)
      Sol Vol   = Solution volume (mL) from Section 3.5.3
      GF, SO2/SO42-   = Gravimetric factor  =  0.667
      Mol Vol   = Molar volume (L/mol)  =  24.45 (25 °C and 760 mmHg)
      AV   = Air volume (L)
      Mol Wt   = Molecular weight for SO2  =  64.0 (g/mol)
      DE   = Desorption efficiency (mass-dependent, see sliding scale below or equation in 3.7.4)
      Amt of SO2 (µg)


      DE Factor


      < 30
      31
      51
      76
      101
      201
      >400
      to
      to
      to
      to
      to
      50
      75
      100
      200
      400
      0.800
      0.825
      0.850
      0.875
      0.900
      0.950
      1.000

      3.7.5. An alternative to the DE correction sliding scale above is the following equation:


      DE  =  -1.1386  ×  10-6 (A)2  +  1.0037  ×  10-3 (A)  +  7.81  ×  10-1

      Where:   A  =  uncorrected µg SO2


      3.7.6. The DE correction may be lot-dependent. The corrections stated in this method were determined using lot no. 673 (Cat. no. 226-80, SKC Inc., Eighty Four, PA) or beaded carbon prepared for sampling phosphine (5.7). A difference in DE was not noted for these two preparations (Section 4.1.2). Future lots or different grades should be evaluated for DE corrections.

      3.8. Reporting Results

      Add the backup section ppm SO2 result (if any) to the front section result for each sample. Report results to the industrial hygienist as ppm SO2.

  1. Backup DataThis method has been validated for a 12-L, 120-min sample taken at a flow rate of 0.1 L/min. The method validation was conducted near the OSHA TWA-PEL and STEL of 2 ppm and 5 ppm, respectively. The sampling tubes used during the validation consisted of a two-section tube (Type I) packed with a 100-mg IABC front and 50-mg backup section or Type II (see Section 2.1.2). Tubes were obtained commercially (Lot no. 673, Cat. no. 226-80, SKC Inc., Eighty Four, PA) or prepared in-house. Preliminary tests were conducted using a 10% (w/w) impregnation of a metal hydroxide base on the carbon bead; however, tests conducted at high humidity (80%) indicated a formation of a slurry inside the sampling tube. The amount of metal hydroxide base was lowered to 1% during validation. A difference in SO2 results using either 1 or 10% base impregnation was not noted; an exception was the 80% RH tests where slurry formation made it difficult to remove the carbon bead from the glass tubes.The validation consisted of the following experiments:
    1. An analysis of 19 samples (6 samples each at 2  ×  and 1  ×  TWA-PEL, and 7 samples at 0.5  ×  TWA-PEL) for the DE study.
    2. A sampling and analysis of 16 samples (6 samples each at 2  ×  and 1  ×  TWA-PEL, and 4 samples at 0.5  ×  TWA-PEL) collected from dynamically generated test atmospheres at 50% RH. Samples at a concentration near the STEL and at concentrations expected during indoor air quality investigations (approximately0.3 ppm) were also taken.
    3. A determination of the sampling media collection efficiency at approximately 4 ppm (2  ×  TWA-PEL).
    4. A determination of breakthrough.
    5. An evaluation of storage stability at 20 to 25 °C for 24 collected samples.
    6. A determination of any significant effects on results when sampling at different humidities.
    7. A determination of the qualitative and quantitative detection limits.
    8. A comparison of methods.
    9. Evaluation of the Type II sampling tube for collecting SO2.
    10. Evaluation of a prefilter/cassette assembly for use with Type I samplers.
    11. Summary.

    All theoretical (known) concentrations of generated test atmospheres were calculated from controlled flows of a cylinder of 303 ppm SO2 in nitrogen (certified concn, Alphagaz, LaPorte, TX) and dilution air. An analysis of the cylinder concentration using OSHA Method No. ID-104 (modified) (5.1) indicated the manufacturer’s stated concentration was accurate. The OSHA method ID-104 was modified such that the 0.3 N H2O2 sample collection solution was made more basic by addition of NaOH. The final collection solution used for the modified method ID-104 was 0.3 N H2O2 in 15 mM NaOH.

    A generation system was assembled, as shown in Figure 1, and used for all experiments except detection limit determinations. Samples using OSHA Method ID-104 (modified) were taken side-by-side with any IABC samples. All samples were analyzed by IC. The IABC samples were subject to the sliding scale DE corrections listed in Section 3.7.3 (with the obvious exception of those samples used to calculate DE corrections in Section 4.1). A correction was not applied nor necessary for the liquid sorbent sampler results (ID-104 modified), or sulfate solutions used to calculate detection limits.

    All results were calculated from concentration-response curves and statistically examined for outliers. In addition, the analysis (Section 4.1) and sampling and analysis results (Section 4.2) were tested for homogeneity of variance. Possible outliers were determined using the Treatment of Outliers test (5.9). Homogeneity of variance was determined using the Bartlett’s test (5.10). Statistical evaluation was conducted according to Inorganic Methods Evaluation Protocol (5.11). The overall error (OE) (5.11) was calculated using the equation:

    OEi  =  ± ( |biasi|  +  2CVi)  ×  100% (95% confidence level)Where i is the respective sample pool being examined.

    4.1. Analysis

    Nineteen samples were prepared by adding known amounts of SO2 to the IABC tubes to determine recoveries (DE) for the analytical portion of the method. For this experiment, an active method of spiking with low-flow (0.03 L/min) sampling pumps was used to determine the amount of gas collected and not necessarily the sampling capability of the IABC at the low-flow rate.

    4.1.1. Procedure:   Sampling tubes containing IABC were spiked using the low flow pumps and generation system as described in references 5.7 and 5.12 The SO2 source mentioned previously was diluted to approximately 30 ppm using the generation system shown in Figure 1. Calibrated low-flow-rate pumps were connected to the sampling manifold and were used to deliver the spikes for measured time periods. Air used to dilute the SO2 source was tempered to 50% RH and 25 °C. Pumps used for this experiment (Miniature Personal Air Sampling Pumps, Model No. 222-3-12, SKC Inc., Eighty Four, PA) were calibrated to collect samples at 0.030 L/min. Spikes were approximately 32, 64, 130, and 400 µg SO2. These levels correspond approximately to 0.5, 1, 2, and 6 times the PEL for a 12-L air sample at a 0.1-L/min flow rate.

    4.1.2. Results:   Desorption efficiencies, presented in Table 1, varied depending on the amount of SO2 collected. For 0.5 times the PEL (32 µg SO2), the DE was close to 0.8; the DE was 1.0 for 6  ×  PEL (approximately400 µg SO2). The DE corrections are similar (although larger) to those found during a previous validation of a sorbent tube (Method no. ID-107, see reference 5.3) for SO2 collection. The previous method used charcoal impregnated in a fashion similar to the IABC sorbent. The average DE correction for the lot of treated charcoal specified in Method no. ID-107 was 0.927, and resulted from averaging DEs of 0.909 (168 µg SO2), 0.934 (333 µg SO2), and 0.940 (669 µg SO2).

    A mechanism to explain the decrease in DE at low mass loadings has not been found; however, it is possible that a portion of the initial SO2 entering the sampling tube strongly bonds with the surface of the carbon bead matrix and becomes unrecoverable. A strong and weak bonding mechanism for SO2 has been noted on active carbon surfaces (5.13). Once the strong bonding sites are occupied, a DE closer to what is expected is achieved. At larger mass loadings the amount of strongly bonded SO2 would remain the same, and become insignificant when compared to the total amount collected; thus the DE approaches unity.

    A test of two different grades of beaded carbon (impregnated) was also conducted and a significant difference in DE was not noted:


    (Sampling Time  =  120 min, flow rate approximately 0.1 L/min,
    SO2 concentration  =  1.19 ppm, 25 °C, 50% RH)

    SKC Bulk


    SKC lot no. 745*


    Grade
    Sample Type
    N
    Mean (ppm SO2)
    Std Dev (ppm SO2)
    CV
    Recovery
    General
    II
    3
    1.19**
    0.015
    0.013
    100%
    MU-AZ
    II
    3
    1.20**
    0.006
    0.005
    101%
    * SKC Catalog no. 226-32 (These tubes were manufactured for the collection of phosphine. The appropriate amount of IABC was removed from a tube, placed in a Type II sampling device, and used to collect SO2).
    ** DE corrected using scale shown in Section 3.7.3.

    Grades listed above are assigned by the manufacturer of the untreated beaded carbon (Kureha Chemical, NY) to designate bead type and manufacturing process used. The general grade is a more common bead which was found to have poor retention efficiency for collection of phosphine (5.7).

    Although the data shows comparable DEs, even for different grades, future lots or grades of beaded carbon should be evaluated for DE corrections.

    4.2. Sampling and Analysis

    To determine the precision and accuracy of the method, known concentrations of SO2 were generated, samples were collected, prepared, and analyzed.

    4.2.1. Procedure:

      1. The SO2 source mentioned previously was used to generate test atmospheres of SO2. This source was diluted with filtered, humidified air using the system shown in Figure 1.
      1. Dynamic generation system
        A Miller-Nelson Research Inc. flow, temperature, and humidity control system (Model HCS-301, Monterey, CA) was used for air flow control and conditioning. All generation system fittings and connections were Teflon®. A glass mixing chamber was used to mix the tempered, filtered air with the contaminant gas. The system was set to generate test atmospheres at 50% RH and 25 °C.
      1. The SO2 and diluent air flow rates were adjusted using mass flow controllers. Flow rates were also measured using a dry test meter (for diluent air) and a soap bubble flow meter (for SO2 gas).
    1. Samples were taken from the sampling manifold using constant-flow pumps. Calibrated P125 and Alpha 2 pumps (E.I. duPont de Nemours & Co., Wilmington, DE) were used. Pump flow rates were approximately 0.1 L/min and sampling time was 120 min. Sample concentrations were approximately 0.5, 1, and 2 times the OSHA TWA-PEL for 12-L air samples. For samples taken near the STEL (approximately5.8 ppm SO2 was used), a 0.1 L/min sampling rate for 15 min was used. For low concentration samples, a test atmosphere of approximately 0.3 ppm was used.

    4.2.2. Results: The results for TWA, STEL, and low concentration-type exposures are shown in Tables 2 and 3a-3b, respectively. The test atmosphere sample (Table 2) and spiked sample (Table 1) results for TWA samples passed the Bartlett’s test and were pooled to determine a total CV (CVT) for the sampling and analytical method. For the experiments, the pooled coefficients of variation, bias, and OE are as follows:

    TWA STEL LOW
    CV   0.048*     0.028**     0.032**
    Bias -3.3% +0.6% -6.5%
    OE ±12.9% ±6.2% ±12.9%
    * CVT(pooled), see reference 5.11 for further details. The CV1 is taken from 0.5, 1, and 2  ×  PEL results. The 6  ×  PEL level is not included in statistical calculations.
    ** CV2 only

    4.3. Collection Efficiency

    Procedure: Six commercially-prepared (Type I) sampling tubes were used for collection at a concentration of approximately 2 times the OSHA TWA-PEL for 120 min at 0.1 L/min (50% RH and 25 °C). The amounts of SO2 vapor collected in the first section (100 mg of sorbent) and second section (50 mg of sorbent) were determined. The collection efficiency (CE) was calculated by dividing the amount of SO2 collected in the first section by the total amount of SO2 collected in the first and second sections.

    Results: The results in Table 4 show a CE of 100%. No SO2 was found in the second sorbent section for the CE experiment.

    4.4. Breakthrough Study

    (Note: Breakthrough is defined as >5% loss of analyte through the sampling media at 50% RH)

    Procedure: Two separate experiments were conducted to test for breakthrough. For the first experiment, the same procedure as the CE test was used with two exceptions:

    1. The concentration was increased to a level approximately 4 times the TWA-PEL (7.20 ppm SO2).
    2. Samples were collected at 0.1 L/min for 240 min.

    The second experiment was conducted using the Type II sampling tube (Section 2.1.2) at a concentration larger than expected during routine sampling of industrial hygiene operations (14.8 ppm SO2). Experimental parameters for this test were: Four Type II sampling tubes, 25 °C, 50% RH, 240-min sampling time, 0.1 L/min sample rate, and 14.8 ppm SO2 test concentration.

    The amount of breakthrough for each sampling tube was calculated by dividing the amount collected in the second section by the total amount of SO2 collected in the first and second sections.

    Results: No breakthrough of SO2 into the second section was found. Results for both concentrations are shown in Table 5.

    4.5. Storage Stability

    Procedure: A study was conducted to assess the storage stability at 20 to 25 °C of the sampling media after SO2 collection. Twenty-four samples were taken near the OSHA TWA-PEL of 2 ppm. After collection, all samples were stored under normal laboratory conditions (20 to 25 °C) on a lab bench and were not protected from light. Six samples were initially desorbed and analyzed, then six samples were desorbed and analyzed after various periods of storage (6, 15, and 32 days).

    Results: The mean of samples analyzed after 32 days was within 10% of the theoretical value as shown in Table 6. A slight increase in recovery over time was noted as shown in the figure below.

    Storage Stability - For problems with accessibility in using figures, illustrations and PDFs in this method, please contact the SLTC at (801) 233-4900.

    4.6. Humidity Study


    Note: Prior to the validation, preliminary humidity tests using a beaded carbon impregnated with a 10% (w/w) load of a metal hydroxide base indicated acceptable SO2 collection at 25 and 50% RH (assuming 25 °C). Although data was also acceptable at 80% RH (2-h sampling time), a slurry developed inside the sampling tube. The resulting slurry presented some difficulty in removing the bead from the sampling tube and required an enhanced attention to technique. The slurry appeared to be a combined result of the following factors:

    1. the hydrophilic nature of the impregnated base,
    2. the hydrophobicity of the beaded carbon, and
    3. complications arising from limited temperature control during sample generations at 80% RH.

    Factor (1) appeared to be the main factor in producing a slurry. The “wetting” effect apparently was assisted by differences in temperature during generation. The high humidity tests were conducted during the winter season and the ambient temperature in the laboratory was about 18 °C. The ambient temperature is normally near the test atmosphere temperature of 25 °C; due to a malfunctioning room thermostat it was somewhat cooler during these tests. The temperature of the sampling tubes are ambient because of the sampling manifold design. The test atmosphere condensation inside the tube probably was accelerated when entering the cooler sampling tube.

    The amount of base impregnation was lowered to 1% (w/w) to alleviate potential formation of a slurry.


    Procedure: A study was conducted to determine any effect on results when samples are collected in different humidities. Samples were taken using the generation system and procedure described in Section 4.2. Test atmospheres were generated at 25 °C and at approximately 0.5, 1, and 2 times the OSHA TWA-PEL. Relative humidities of 30%, 50%, and 80% were used at each concentration level tested.

    Results: Results of the humidity tests are listed in Table 7. An F test was used to determine if any significant effect occurred when sampling at different humidities. As shown, the calculated F values exceeded critical F values (5.14) for all the concentrations tested and a significant difference in results occurred across the humidity ranges tested. An examination of the data indicates a decrease in recoveries as humidity increases; however, a correction for humidity effect was not instituted because results at higher humidities were considered acceptable in terms of overall error (< ±25%).

    The finding that increasing humidity produces a decrease in the amount of sulfate found appears to contradict previous findings in the literature (5.15). The previous study (5.15) indicated the conversion of SO2 to sulfate on an active carbon surface was facilitated by the presence of an aqueous environment; however, testing carbons impregnated with a metal hydroxide base was not performed. The base appears to significantly alter the adsorption characteristics of the beaded carbon for SO2.

    4.7. Qualitative and Quantitative Detection Limit Study

    Procedure: Low concentration samples were prepared by spiking desorbing solutions (Section 3.3.4) with aliquots of aqueous standards prepared from sodium sulfate. These samples were analyzed using a 50-µL sample injection loop and a detector setting of 1 microsiemens (µS). A derivation of the International Union of Pure and Applied Chemistry (IUPAC) detection limit equation (5.16) was used for this study.

    Results: The results are shown in Table 8 for qualitative and quantitative detection limits, respectively. The qualitative limit is 0.0187 µg/mL as SO42- at the 99.86% confidence level. The quantitative limit (99.99% confidence) is 0.0642 µg/mL as SO42-. Using a 12-L air volume and a 10-mL sample solution volume, the qualitative limit is 0.004 ppm and the quantitative limit is 0.013 ppm as SO2.

    4.8. Comparison of Methods

    Procedure: In order to compare the performance of this method and to confirm the theoretical SO2 concentrations, an independent method (OSHA Method no. ID-104 for SO2, modified) was used. The collection solution for Method ID-104 was modified as previously mentioned in Section 4, and impingers were used to collect samples. The IABC and impinger samples were collected side-by-side from the generation system. All samples were analyzed by IC.

    Results: Table 9 shows the results for different SO2 concentrations. As shown, the theoretical concentration of the generation system, the IABC, and impinger results are in good agreement.

    4.9. Type II Tube Study

    Procedure: Eight Type II sampling tubes (see Section 2.1.2 for a description of this tube) were chosen for a statistical study using the generation system described in Section 4.2. These tubes contained PTFE membranes as prefilters. Samples were collected side-by-side with impinger samples at 25 °C, 80% RH, and at approximately the OSHA TWA-PEL for 120 min. The high humidity was selected as a worst-case test (Section 4.6).

    Results: Results are listed in Table 10. As shown, the Type II sampling device can be used to collect SO2 without significantly altering the concentration. A slight increase in recovery was noted when compared to the earlier Type I tube results at 80% RH (Section 4.6).

    4.10. Prefilter Evaluation

    Procedure: Past research regarding aerosols (5.17) has indicated that particulate in the air sampled may penetrate any glass wool plugs and deposit on the sorbent when using conventional sampling tubes. To remedy this, a prefilter is generally used to stop the particulate before entry into the sampling tube. A preliminary experiment was conducted using the Type II sampling tube with glass fiber prefilters instead of PTFE. Significant losses were noted and were apparently caused by the slightly basic glass fiber filters reacting with some of the SO2.

    To further evaluate the possibility of SO2 reacting with a prefilter/cassette sampling device, an experiment was performed using six Type I sampling tubes with prefilter sampling assemblies consisting of PTFE filter/polypropylene backup pad/carbon-filled cassettes. These cassettes (as specified in Section 2.1.5) have enjoyed popularity for asbestos sampling (5.18) and for their limited reactivity to certain corrosive gases (5.19).

    The test was conducted by taking six IABC samples without prefilters side-by-side with six IABC with prefilters. Samples were taken such that the test atmosphere entered the prefilter assembly first and then entered the IABC with minimal contact at the connection between cassette and sampling tubes. Small pieces of Tygon® tubing were used to connect the cassettes and IABC sampling tubes. All samples were taken at a flow rate of about 0.1 L/min for 120 min. The generation system concentration was approximately the TWA-PEL.

    Results: The results of the comparison of IABC samples taken with and without prefilters is shown in Table 11. As shown, a difference in the amount of SO2 collected was not noted between the prefilter/IABC and IABC sampling assembly. The PTFE prefilter/cassette assembly does not appear to inhibit the collection of SO2 when using the stated sampling conditions.

    4.11. Summary

    The validation results indicate the method meets both the NIOSH and OSHA criteria for accuracy and precision (5.10, 5.11). Collection efficiency, breakthrough, and storage stability are adequate. Although it appears that humidity effects are significant when sampling at different humidities, the results are within an acceptable range (OE < ±25%). Detection limits are adequate when samples are taken for 120 min at 0.1 L/min, or for 15-min STEL determinations. The method is adequate for monitoring TWA, STEL, and indoor air types of exposures.

    The contaminant levels of blank IABC samples, when compared to levels found in the sorbent used in OSHA Method no. ID-107, were significantly lower. Blanks from IABC sorbent contained only 1 to 2 µg background (as SO42-), based on a sample solution volume of 10 mL. The previous impregnated charcoal sorbent contamination ranged from 20 to 100 µg SO42-.

  2. References

    5.1. Occupational Safety and Health Administration Salt Lake Technical Center: Sulfur Dioxide in Workplace Atmospheres (Bubbler) (USDOL/OSHA Method No. ID-104.) In OSHA Analytical Methods Manual 2nd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 1991.5.2. Smith, D.L., W.S. Kim, and R.E. Kupel: Determination of Sulfur Dioxide by Adsorption on A Solid Sorbent Followed by Ion Chromatography Analysis. Am. Ind. Hyg. Assoc. J. 41:485-488 (1980).5.3. Occupational Safety and Health Administration Analytical Laboratory: Sulfur Dioxide in Workplace Atmospheres (Solid Sorbent) (USDOL/OSHA Method No. ID-107). In OSHA Analytical Methods Manual 1st ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.5.4. Patty, F.A.; Ed. Industrial Hygiene and Toxicology, 2nd rev. ed. Vol. 2. New York: Interscience, 1963.5.5. National Institute for Occupational Safety and Health: Criteria for a Recommended Standard – Occupational Exposure to Sulfur Dioxide[DHEW (NIOSH) Publication No. 74-111]. Washington, D.C.: U.S. Government Printing Office, 1974.

    5.6. “Sulfur Dioxide” Federal Register 54:12 (19 Jan. 1989). pp 2524-2527

    5.7. Occupational Safety and Health Administration Salt Lake Technical Center: Phosphine in Workplace Atmospheres (and Backup Data Report) (USDOL/OSHA Method No. ID-180). In OSHA Analytical Methods Manual 2nd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 1991.

    5.8. Occupational Safety and Health Administration Salt Lake Technical Center: Ion Chromatography Standard Operating Procedure (Ion Chromatographic Committee). Salt Lake City, UT. In progress.

    5.9. Mandel, J.: Accuracy and Precision, Evaluation and Interpretation of Analytical Results, The Treatment of Outliers. In Treatise On Analytical Chemistry, 2nd ed., Vol.1, edited by I. M. Kolthoff and P. J. Elving. New York: John Wiley and Sons, 1978. pp. 282-285.

    5.10. National Institute for Occupational Safety and Health: Documentation of the NIOSH Validation Tests by D. Taylor, R. Kupel, and J. Bryant (DHEW/NIOSH Pub. No. 77-185). Cincinnati, OH: National Institute for Occupational Safety and Health, 1977. pp. 1-12.

    5.11. Occupational Safety and Health Administration Analytical Laboratory: Precision and Accuracy Data Protocol for Laboratory Validations. In OSHA Analytical Methods Manual 1st ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.

    5.12. National Institute for Occupational Safety and Health: Backup Data Report No. S332 for Phosphine, Attachment A. Cincinnati, OH: National Institute for Occupational Safety and Health, 1977 (unpublished).

    5.13. Davini, P.: Adsorption and Desorption of SO2 on Active Carbon: The Effect of Surface Basic Groups. Carbon 28:565-571 (1990).

    5.14. Dowdy, S. and S. Wearden: Statistics for Research. New York: John Wiley and Sons, 1983. Chapter 8.

    5.15. Halstead, J.A., R. Armstrong, B. Pohlman, S. Sibley, and R. Maier: Nonaqueous Heterogeneous Oxidation of Sulfur Dioxide. J. Phys. Chem. 94:3261-3265 (1990).

    5.16. Long, G.L. and J.D. Winefordner: Limit of Detection — A Closer Look at the IUPAC Definition. Anal.Chem. 55:712A-724A (1983).

    5.17. Fairchild, C.I., and M.I. Tillery: The Filtration Efficiency of Organic Vapor Sampling Tubes against Particulates. Am. Ind. Hyg. Assoc.J. 38:277-283 (1977).

    5.18. Occupational Safety and Health Administration Salt Lake Technical Center: Asbestos (USDOL/OSHA Method No. ID-160). In OSHA Analytical Methods Manual 2nd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 1991.

    5.19. Cassenelli, M.E.: Development of a Solid Sorbent Monitoring Method for Chlorine and Bromine in Air with Determination by Ion Chromatography. Appl. Occup. Environ. Hyg. 6:215-226 (1991).


Table 1

Sulfur Dioxide Analysis – [Desorption Efficiency (DE)]


(OSHA-PEL)
Taken
(µg SO2)
Found
(µg SO2)
Recovery
(F/T)
  N Mean DE Std Dev CV1

(0.5 × PEL)
31.850
32.090
32.090
32.090
32.090
32.090
32.090
25.330
24.280
26.730
28.290
24.930
25.530
25.610
0.795
0.757
0.833
0.882
0.777
0.796
0.798
7 0.805 0.041 0.051
(1 × PEL)
64.200
64.200
64.200
64.200
64.350
65.820
52.080
52.850
54.580
54.210
53.680
54.430
0.811
0.823
0.850
0.844
0.834
0.827
6 0.832 0.014 0.017
(2 × PEL)
131.340
131.340
131.340
131.340
131.340
128.400
113.960
116.950
111.350
116.130
120.030
115.780
0.868
0.890
0.848
0.884
0.914
0.902
6 0.884 0.024 0.027
(6 × PEL)
386.130
394.960
403.320
450.430
409.050
435.440
374.590
408.760
407.880
380.990
395.910
439.590
0.970
1.035
1.011
0.846*
0.968
1.010
5 0.999 0.030 0.030

*Outlier, was deleted from final statistical calculations

F/T  =  Found/Taken         DE  =  Desorption Efficiency

CV1 (Pooled)  =  0.036 (Calculated from pooling 0.5, 1, and 2  ×  PEL data only)

The mean DEs were significantly less than 1.0; therefore, a DE correction is needed. No corrections are necessary for SO2 >400 µg.

Table 2

Sampling and Analysis – TWA Determination*

(25 °C and 50% RH)


(OSHA-PEL)
Taken
(ppm SO2)
Found
(ppm SO2)
Recovery
(F/T)
  N Mean DE Std Dev CV2 OE

(0.5 × PEL)
1.360
1.360
1.360
1.360
1.340
1.420
1.280
1.350
0.985
1.044
0.941
0.993
4 0.991 0.042 0.043   9.4
(1 × PEL)
2.400
2.400
2.400
2.400
2.400
2.400
2.190
2.390
2.400
2.360
2.420
2.280
0.912
0.996
1.000
0.983
1.008
0.950
6 0.975 0.037 0.038 10.0
(2 × PEL)
4.160
4.160
4.160
4.160
4.160
4.160
4.040
3.690
4.070
3.870
3.690
4.210
0.971
0.887
0.978
0.930
0.887
1.012
6 0.944 0.051 0.054 16.5

F/T  =  Found/Taken OE   = Overall error (±%)
Bias   = -0.033
CV2 (Pooled)   = 0.046
CVT (Pooled)   = 0.048
Overall Error (Total)   = 12.9%
*Samples were taken for 2 h.

Table 3a

Sampling and Analysis – STEL Determination

(25 °C and 50% RH)


Sample No. Air Vol Found Taken —————- Statistical Analysis —————–
(L) (—ppm SO2—)   N Mean Std Dev CV Recovery (%)

1
2
3
4
1.33
1.32
1.50
1.33
5.26
5.35
5.56
5.22
5.32
5.32
5.32
5.32
4 5.35 0.15 0.028 100.6

Table 3bSampling and Analysis – Low Concentration

(25 °C and 50% RH)


Sample No. Air Vol Found Taken —————- Statistical Analysis —————–
(L) (—ppm SO2—)   N Mean Std Dev CV2 Recovery (%)

1
2
3
4
5
6
12.0
12.6
11.0
12.0
12.6
11.3
0.288
0.288
0.300
0.288
0.300
0.275
0.310
0.310
0.310
0.310
0.310
0.310
6 0.290 0.009 0.032 93.5*

* A DE correction of 0.8 was used from the scale listed in Section 3.7.4 Low mass loadings (<30 µg) may be more accurately corrected using the equation discussed in Section 3.7.5.

Table 4

Collection Efficiency

(2  ×  TWA-PEL, 25 °C & 50% RH)


——- ppm SO2 Found ——–
Sample No. First Section Second Section % Collection Efficiency

1
2
3
4
5
6
4.04
3.69
4.07
3.87
3.69
4.21
ND
ND
ND
ND
ND
ND
100.0
100.0
100.0
100.0
100.0
100.0
Notes:   (a) Sampled at 0.1 L/min for 120 min.
(b) Samples were desorbed using a sample solution volume  =  10.0 mL
(c) ND  =  None detectable (<0.2 µg/mL as SO42-)

Table 5

Breakthrough Study

(25 °C and 50% RH)


——- ppm SO2 Found ——–
Sample No. First Section Second Section % Breakthrough

1
2
3
4
5
6
7
8
  7.28
6.09
6.97
7.27
15.08
15.10
14.28
13.64
ND
ND
ND
ND
ND
ND
ND
ND
0
0
0
0
0
0
0
0
Notes:   (a) Sampled at 0.1 L/min for 240 min.
(b) Samples were desorbed using a sample solution volume  =  10.0 mL. A 10-fold dilution of sample solution was performed on samples 5-8.
(c) ND  =  None detectable (<0.004 ppm SO2)
(d) Samples 1-4 used Type I sampling device; samples 5-8 used Type II

Table 6

Storage Stability Test – SO2

(1  ×  TWA-PEL, 25 °C, and 50% RH)


Day Air Vol Found Taken —————- Statistical Analysis —————–
(L) (—ppm SO2—)   N Mean Std Dev CV Recovery (%)

0 11.5
10.6
10.7
11.5
10.6
11.5
2.19
2.39
2.40
2.36
2.42
2.28
2.40
2.40
2.40
2.40
2.40
2.40
6 2.34 0.088 0.038 97.5
6 11.9
10.5
10.6
11.7
10.3
10.4
2.21
2.44
2.26
2.33
2.43
2.34
2.39
2.39
2.39
2.39
2.39
2.39
6 2.34 0.091 0.039 97.9
15 11.8
10.5
10.6
11.8
10.5
10.6
2.34
2.64
2.32
2.31
2.51
2.43
2.35
2.35
2.35
2.35
2.35
2.35
6 2.43 0.130 0.054 103
32* 8.2
7.9
8.0
8.2
7.9
8.0
2.62
2.46
2.52
2.58
2.56
2.45
2.35
2.35
2.35
2.35
2.35
2.35
6 2.53 0.068 0.027 108
* 90-min sampling time was used for this test only. The rest of the samples were taken for 120 min.

Table 7

Humidity Test – SO2

(0.5  ×  TWA-PEL & 25 °C)


% RH


    30


    50


    80


ppm SO2 Taken 0.990 1.48 1.19
ppm SO2 Found 1.08
0.994
0.998
1.13
1.05
1.11
1.33
1.41
1.27
1.35
1.02
1.04
1.05
1.05
1.10
1.02
N
Mean (ppm)
Std Dev (ppm)
CV
Ave Recovery
6
1.06
0.057
0.054
107%
4
1.34
0.058
0.043
90.5%
6
1.05
0.029
0.028
88.0%

At the 99% confidence level:
Fcrit  =  6.70 Fcalc  =  33.81 (2, 13 degrees of freedom)
Fcrit  <   Fcalc; therefore, a significant difference in results was noted across the humidity levels tested.

Table 7 (Continued)

Humidity Test – SO2

(1  ×  TWA-PEL & 25 °C)


% RH


    30


    50


    80


ppm SO2 Taken 2.33 2.40 2.48
ppm SO2 Found 2.44
2.50
2.48
2.48
2.32
2.51
2.19
2.39
2.40
2.36
2.42
2.28
2.25
2.26
2.20
2.40
2.19
2.36
N
Mean (ppm)
Std Dev (ppm)
CV
Ave Recovery
6
2.46
0.070
0.029
105%
6
2.34
0.088
0.038
97.5%
6
2.28
0.085
0.038
91.8%

At the 99% confidence level:
Fcrit  =  6.36 Fcalc  =  24.22 (2, 15 degrees of freedom)
Fcrit  <   Fcalc; therefore, a significant difference in results was noted across the humidity levels tested.
Table 7 (Continued)Humidity Test – SO2(2  ×  TWA-PEL & 25 °C)

% RH


    30


    50


    80


ppm SO2 Taken 4.44 4.40 4.40
ppm SO2 Found 4.28
4.32
4.25
4.41
4.72
4.59
4.04
3.69
4.07
3.87
3.57
4.21
4.03
3.67
3.94
3.81
3.96
N
Mean (ppm)
Std Dev (ppm)
CV
Ave Recovery
6
4.43
0.188
0.042
99.7%
6
3.91
0.244
0.062
88.8%
6
3.88
0.143
0.037
88.2%

At the 99% confidence level:
Fcrit  =  6.52 Fcalc  =  11.88 (2, 14 degrees of freedom)
Fcrit  <   Fcalc; therefore, a significant difference in results was noted across the humidity levels tested.

Table 8

Qualitative and Quantitative Detection Limits (IUPAC Method)


———– SO2 (as SO42-) Level ————–
Sample No. Rbl
PA
0.05 µg/mL
PA
0.10 µg/mL
PA

1
2
3
4
5
6
1.07
1.14
0.87
1.24
1.25
1.21
6.32
5.91
6.39
5.98
5.81
6.38
13.66
13.04
13.19
13.32
13.35
13.96
N
Mean
Std Dev
CV
6
1.13
0.14
0.128
6
6.13
0.26
0.042
6
13.42
0.34
0.025
PA  =  Integrated Peak Area (SO42-) / 1,000,000
Rbl  =  Reagent Blank

Using the equation:            Cld  =  k(sd) / m

Where:
Cld = the smallest reliable detectable concentration an analytical instrument can determine at a given confidence level.
k =
=
  3 (Qualitative Detection Limit, 99.86% Confidence)
10 (Quantitative Detection Limit, 99.99% Confidence)
sd = standard deviation of the reagent blank (Rbl) readings.
m = analytical sensitivity or slope as calculated by linear regression.
Cld =   3(0.14) / 22.45 = 0.0187 µg/mL as SO42- for the qualitative limit.
Cld = 10(0.14) / 22.45 = 0.0624 µg/mL as SO42- for the quantitative limit.
Qualitative detection limit = 0.187 µg SO42- (10-mL sample volume) or
0.004 ppm SO2 (12-L air volume).
Quantitative detection limit = 0.624 µg SO42- (10-mL sample volume) or
0.013 ppm SO2 (12-L air volume).


Table 9

Summary – Comparison of Methods for SO2

(50% RH & 25 °C)


Set#


Method


SO2 Concn (ppm)


  N


Std Dev


1 THE
104M
IABC
1.36
1.36
1.35
6
4
0.156
0.057
2 THE
104M
IABC
2.40
2.31
2.34
6
6
0.058
0.058
3 THE
104M
IABC
4.40
4.16
3.93
5
6
0.358
0.214
4 THE
104M
IABC
5.32
5.79
5.35
6
4
0.497
0.152
Notes:   (a) THE  = Theoretical (Taken) value, calculated from certified SO2 cylinder and gas generation system flows.
(b) 104M  = Impinger samples taken using OSHA Method No. ID-104 (modified).
(c) IABC  = Impregnated activated beaded carbon

Table 10

Sampling and Analysis – Type II Sampling Tube

(1  ×  TWA-PEL, 25 °C, and 80% RH)


Sample No. Air Vol Found Taken —————- Statistical Analysis —————–
(L) (—ppm SO2—)   N Mean Std Dev CV Recovery (%)

1
2
3
4
5
6
7
8
10.6
10.3
11.3
12.7
10.6
10.3
11.3
12.7
 1.65*
2.08
2.23
2.16
1.91
2.14
1.98
2.10
2.23
2.23
2.23
2.23
2.23
2.23
2.23
2.23
7 2.09 0.11 0.052 93.6
*Outlier, not used in statistical analysis
Sample
Set
#
With Pre-filter


Without Pre-filter


Air Vol, L ppm SO2 Found Air Vol, L ppm SO2 Found

1
2
3
4
5
6
12.1
12.1
11.2
11.8
11.1
12.3
1.80
1.62
2.04
1.92
1.79
1.89
11.8
11.1
12.3
*
12.1
11.2
1.79
1.71
1.961.84
1.95
N
Mean
Std Dev
CV
6
1.84
0.14
0.077
5
1.85
0.11
0.058
*Pump stopped during sampling
Notes:   (a) Sampling Time  =  120 min
(b) Flow Rate approximately0.1 L/min
(c) Sample Solution Volume for Desorption  =  10 mL

Block Diagram of the Laboratory Generation System   [Text Version]Figure 1: Block Diagram of the Laboratory Generation System - For problems with accessibility in using figures, illustrations and PDFs in this method, please contact the SLTC at (801) 233-4900.


The system shown above provided a means for generating dynamic test atmospheres. The system consists of four essential elements:

  1. a flow-temperature-humidity control system,
  2. an SO2 vapor generating system,
  3. a mixing chamber, and
  4. an active sampling manifold.


Text Version

Lab Air
 —–>
Air Purifier
 —–>

 

Flow-Temp-Humidity
Control System

 

<—–
Ionic Exchange
Column
<—–
Lab Air
|
|
V
SO2
Cylinder
————
->->->->
————
Mixing Chamber
|
|
V
Active Sampling Manifold
|
|
V
Dry Gas Meter
  —–>
Exhaust
————
->->->->
————
  =    Mass Flow Controller

Sulfur Dioxide (SO2) – Thông tin chung và tác động môi trường

Sulfur Dioxide (SO2) is one of a group of gases called sulfur oxides (SOx). While all of these gases are harmful to human health and the environment, SO2 is of greater concern.

Sulfur Dioxide Basics

What is SO2 and how does it get in the air?

What is SO2?

EPA’s national ambient air quality standards for SO2 are designed to protect against exposure to the entire group of sulfur oxides (SOx).  SO2 is the component of greatest concern and is used as the indicator for the larger group of gaseous sulfur oxides (SOx).  Other gaseous SOx (such as SO3) are found in the atmosphere at concentrations much lower than SO2.

Control measures that reduce SO2 can generally be expected to reduce people’s exposures to all gaseous SOx.  This may have the important co-benefit of reducing the formation of particulate SOx such as fine sulfate particles.

Emissions that lead to high concentrations of SO2 generally also lead to the formation of other SOx. The largest sources of SO2 emissions are from fossil fuel combustion at power plants andother industrial facilities.

How does SO2 get in the air?

The largest source of SO2 in the atmosphere is the burning of fossil fuels by power plants and other industrial facilities. Smaller sources of SO2 emissions include: industrial processes such as extracting metal from ore; natural sources such as volcanoes; and locomotives, ships and other vehicles and heavy equipment that burn fuel with a high sulfur content.

What are the harmful effects of SO2?

SO2 can affect both health and the environment.

What are the health effects of SO2?

Short-term exposures to SO2 can harm the human respiratory system and make breathing difficult. Children, the elderly, and those who suffer from asthma are particularly sensitive to effects of SO2.

SO2 emissions that lead to high concentrations of SO2 in the air generally also lead to the formation of other sulfur oxides (SOx). SOx can react with other compounds in the atmosphere to form small particles. These particles contribute to particulate matter (PM) pollution: particles may penetrate deeply into sensitive parts of the lungs and cause additional health problems.

What are the environmental effects of SO2 and other sulfur oxides?

At high concentrations, gaseous SOx can harm trees and plants by damaging foliage and decreasing growth.

SO2 and other sulfur oxides can contribute to acid rain which can harm sensitive ecosystems.

Visibility

SO2 and other sulfur oxides can react with other compounds in the atmosphere to form fine particles that reduce visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.

Deposition of particles can also stain and damage stone and other materials, including culturally important objects such as statues and monuments.

What is being done to reduce SO2 pollution?

EPA’s national and regional rules to reduce emissions of SO2 and pollutants that form sulfur oxides (SOx) will help state and local governments meet the Agency’s national air quality standards.

EPA identifies areas where the air quality does not meet EPA SO2 standards. For these areas, state, local, and tribal governments develop plans to reduce the amount of SO2 in the air.

Setting and Reviewing Standards to Control SO2 Pollution

What are SO2 standards?

National Ambient Air Quality Standards (NAAQS) for SO2 specify maximum amounts of sulfur dioxide to be present in outdoor air. Limiting SO2 in the air protects human health and the environment.

  • See primary NAAQS for SO2for an in-depth explanation of the current SO2 primary (health-based) standards, including Federal Register citations and fact sheets.
  • See secondary NAAQS for SO2for an in-depth explanation of the current SO2 secondary (welfare-based) standard and EPA’s most recent joint review of the secondary standards for SO2 and nitrogen dioxide (NO2).

How are the standards developed and reviewed?

The Clean Air Act requires EPA to set national ambient air quality standards for sulfur oxides as one of the six criteria pollutants.  The NAAQS for sulfur oxides are currently set using SO2 as the indicator of the larger group of sulfur oxides. The law also requires EPA to periodically review the standards and revise them if appropriate to ensure that they provide the requisite amount of health and environmental protection and to update those standards as necessary.

What scientific and technical information supports reviews?

The various documents published during the review process include multiple drafts of plans and assessments, reports from the Clean Air Scientific Advisory Committee (CASAC), and Federal Register notices.

Applying or Implementing Sulfur Dioxide Standards

Designations: how do we know if an area is not meeting SO2 standards?

Areas within each state are “designated” as either meeting (attaining) sulfur dioxide (SO2) standards or not meeting them. In some cases, an entire state may attain a standard.

Those areas that exceed the standards are known as “nonattainment areas.” Nonattainment areas for SO2 and the other criteria air pollutants are listed in the Green Book.

Along with developing the SO2 standards themselves (part of the National Ambient Air Quality Standards, or NAAQS), EPA also develops requirements for how to go about attaining and maintaining those standards:

What are the state implementation plan (SIP) requirements?

Air quality standards get applied, or implemented, through controlling air pollution from emission sources. Each state is required to develop a plan for how they will control air pollution within their jurisdiction. This plan is called a State Implementation Plan (SIP).

In general, the SIP consists of

  • programs, including
    • air quality monitoring
    • air quality modeling
    • emission inventories
    • emission control strategies
  • and documents (policies and rules)

that the state uses to attain and maintain the NAAQS.

A state must engage the public, through notices and public hearings, before sending the SIP to EPA for approval. Tribes may develop plans if they choose to do so, otherwise EPA will develop an implementation plan for them. Learn more Basics of SIP Requirements

  • Learn more about the NAAQS implementation process
  • SIP Status for each State, including tribal implementation plans (TIPs): EPA evaluates the submitted SIPs, then issues a notice, indicating that either the SIP has been approved or needs additional work. Once the SIP has been approved, the state implements its air pollution control strategies to gradually reduce sulfur dioxide pollution.

How do states develop SIPs and start attaining the standards?

  • EPA’s checklist guide to preparing a sulfur dioxide SIP: State, local, and tribal air quality agencies can find assistance in developing their plans to implement SO2 Tools include timeframes for submitting parts of the SIP, and how to use emissions data to demonstrate progress in reducing SO2.
  • Redesignations and Clean Data Policy (CDP): States with areas that are starting to monitor attainment can demonstrate attainment using air quality modeling and other analyses.
  • Training resourcesinclude various presentations and webinars to explain the implementation process and assist the air agencies.
  • EPA evaluates the submitted SIPs, then issues a notice, indicating that either the SIP has been approved or needs additional work. Once the SIP has been approved, the state implements its air pollution control strategies to gradually reduce SO2Get information about the SIP status for each state.

Nguồn: https://www.epa.gov

Ô nhiễm không khí là sự thay đổi lớn trong thành phần của không khí, chủ yếu do khói, bụi, mồ hóng, hơi hoặc các khí lạ làm cho không khí không sạch, có sự tỏa mùi, làm giảm tầm nhìn xa, gây biến đổi khí hậu, gây bệnh cho con người và sinh vật.

Ô nhiễm không khí khiến hơn 3 triệu người chết sớm mỗi năm, nó đe dọa gần như toàn bộ cư dân thành phố lớn tại những nước đang phát triển. Theo đài Fox News 80% các thành phố trên thế giới không đáp ứng được tiêu chuẩn của Tổ chức Y tế Thế giới (WHO) về chất lượng không khí, trong đó chủ yếu tập trung ở các nước nghèo. WHO cho biết mức độ ô nhiễm không khí đô thị toàn cầu đã tăng 8% bất chấp những cải thiện ở một số vùng. Điều này dẫn đến nguy cơ đột quỵ, bệnh tim mạch, ung thư phổi cùng hàng loạt vấn đề về đường hô hấp.

Tác nhân gây ô nhiễm không khí:

  • Các loại khí oxit: CO, CO2, SO2, NOx…
  • Các hợp chất khí halogen: HCl, HF, HBr
  • Các chất hữu cơ tổng hợp RH, bay hơi xăng, sơn
  • Các khí quang hóa: PAN, O3
  • Các chất lơ lửng: sương mù, bụi,khí thải sinh hoạt như than bếp
  • Nhiệt, phóng xạ

Nguồn: Wikipedia®