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Passive Sampling of Nitrogen Dioxide and Sulfur Dioxide in Ambient Air of Chiang Mai

Passive Sampling of Nitrogen Dioxide and Sulfur Dioxide in Ambient Air of Chiang Mai. Shakya, K.M. 1 , P. Thavornyutikarn 1 , S. Chantara 1 , W. Saipunkaew 1 , H. Mosbaek 2. 7 December 2004. Environmental Science Program, Faculty of Science, Chiang Mai University, Thailand

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Passive Sampling of Nitrogen Dioxide and Sulfur Dioxide in Ambient Air of Chiang Mai

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  1. Passive Sampling of Nitrogen Dioxide and Sulfur Dioxide in Ambient Air of Chiang Mai Shakya, K.M.1, P. Thavornyutikarn1, S. Chantara1, W. Saipunkaew1, H. Mosbaek2 7 December 2004 • Environmental Science Program, Faculty of Science, Chiang Mai University, Thailand • Technical University of Denmark, Denmark

  2. 1. Introduction Passive Sampling • First described by Palmes et al. (1976) in occupational hygiene for measuring NO2 in indoor air • Based on diffusion principle • Collection of gas on sampling medium soaked with absorbent by chemical absorption (Krupa and Legge, 2000) • Sampling medium – filter papers or steel meshes • Absorbent – depends on gas of interest

  3. Advantages Disadvantages • Long sampling time • No standard procedures • Inability to obtain short-term peaks • Possibility of interferences from meteorology • Doubts on reliability • Light, cheap, robust, easy to operate • Small, soundless and reusable • On-site power and pumping of air not required • Do not require attention during sampling • Supports “green analytical chemistry“ • Favors to have many sampling sites • Very appropriate for large scale monitoring

  4. Objectives of this research • To determine the accuracy of passive samplers by comparing with active samplers, • To compare the results among different kinds of passive samplers, • To compare the results of NO2 concentrations from spectrophotometer and ion chromatograph, and • To determine the levels of NO2 and SO2 concentrations in ambient air using passive samplers in Chiang Mai city

  5. 2. Experimental Preparation of diffusion tubes • diffusion tubes – polystyrene (ps), polyethylene (pe), and “Gradko” tubes • Sampling medium - Whatman no. 40 filter paper • Absorbents for NO2 – TEA and NaOH plus NaI • Absorbents for SO2 – TEA, Na2CO3, and NaOH • Installation of diffusion tubes inside the polyethylene box at 1.5 m above ground level • 3-9 sampling sites • Sampling period – October 2003 to February 2004

  6. Diagram of diffusion tube TEA coated filter paper 5.4 cm 5.4 cm 1.2 cm 1.3 cm Polyethylene cap Polystyrene tube Polyethylene tube

  7. Analysis of NO2- by spectrophotometer • Extraction with DI water • Color formation with reagent mixture (Sulfanilamide + N-1 naphthyl ethylene diamine hydrochloride solution) • Measured at 540 nm on PerkinElmer Lambda 25 Spectrophotometer Analysis of NO2- and SO42- by Ion Chromatograph • Extraction with Milli-Q water • Oxidation with 0.15% H2O2 • eluent: 1.80 mM Na2CO3/ 1.70 mM NaHCO3 • 1.5 ml/min eluent flow rate • 3 s background conductivity • 25 l sample loop volume • BDS, Barspec Data System

  8. 3. Results & Discussion PE tubes - 14.22% > PS tubes Correlation between NO2 measurements by PS and PE tubes (Analysis by Spectrophotometer)

  9. PE tubes - 1.95% > PS tubes Correlation between SO2 measurements from 4 weeks exposure of PS and PE tubes

  10. PS tubes - 1. 62% > PE tubes Correlation between SO2 measurements from 2 weeks exposure of PS and PE tubes

  11. NO2 measurements (01/22/2004 – 02/05/2004)

  12. SO2 measurements (01/22/2004 – 02/19/2004)

  13. Underestimation:54.13% PS tubes and 15.39% PE tubes Correlation between NO2 measurements from active and passive sampling for 2 weeks period

  14. Detection limits for instrument • Spectrophotometer • 0.09 g/ml NO2- • Ion Chromatograph • DL: 0.04 g/ml NO2- and 0.02 g/ml SO42- • Minimum Detectable Quantity: 0.48 g.sec NO2- and 0.36 g.sec SO42- Detection limits for passive sampling method • NO2: 1.6 g/m3 for PS and 3.9 g/m3 for PE tubes • SO2 (2 weeks): 1.9 g/m3 for PS and 1.7 g/m3 for PE tubes • SO2 (4 weeks): 1.4 g/m3 for PS and 2.1 g/m3 for PE tubes

  15. 4. Conclusion • Diffusion tubes (ps and pe) showed good trends of NO2 and SO2 concentrations • Good correlation between ps and pe tubes • Good correlation between active and passive sampling measurements for NO2 but variable for SO2 • Underestimation for NO2 and overestimation for SO2 by diffusion tubes compared to active sampling; also supported by “Gradko” tubes • Variations in blank measurements • Precision - 18.12% for NO2 and 16.36% for SO2

  16. Errors can be reduced for diffusion tubes : • Use of protective shelters • Keeping tubes in an airtight containers during transit • Storage of tubes in a refrigerator and not storing for very long time • Diffusion tubes with separate cap and body parts • Use of a porous membrane at mouth of the tube • Good laboratory practice

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