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

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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

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Passive Sampling
1. Introduction

• 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

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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

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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

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Preparation of diffusion tubes
2. Experimental

• 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

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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
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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

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3. Results Discussion
PE tubes - 14.22 gt PS tubes
Correlation between NO2 measurements by PS and PE
tubes (Analysis by Spectrophotometer)
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PE tubes - 1.95 gt PS tubes
Correlation between SO2 measurements from 4 weeks
exposure of PS and PE tubes
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PS tubes - 1. 62 gt PE tubes
Correlation between SO2 measurements from 2 weeks
exposure of PS and PE tubes
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NO2 measurements (01/22/2004 02/05/2004)
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SO2 measurements (01/22/2004 02/19/2004)
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Underestimation54.13 PS tubes and 15.39 PE
tubes
Correlation between NO2 measurements from active
and passive sampling for 2 weeks period
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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

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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

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• 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