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 Environmental Science Program, Faculty of Science, Chiang Mai University, Thailand 2.Technical University of Denmark, Denmark

Passive Sampling First described by Palmes et al. (1976) in occupational hygiene for measuring NO 2 in indoor air First described by Palmes et al. (1976) in occupational hygiene for measuring NO 2 in indoor air Based on diffusion principle Based on diffusion principle Collection of gas on sampling medium soaked with absorbent by chemical absorption (Krupa and Legge, 2000) Collection of gas on sampling medium soaked with absorbent by chemical absorption (Krupa and Legge, 2000) Sampling medium – filter papers or steel meshes Sampling medium – filter papers or steel meshes Absorbent – depends on gas of interest Absorbent – depends on gas of interest 1. Introduction

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

Objectives of this research To determine the accuracy of passive samplers by comparing with active samplers, 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 among different kinds of passive samplers, To compare the results of NO 2 concentrations from spectrophotometer and ion chromatograph, and To compare the results of NO 2 concentrations from spectrophotometer and ion chromatograph, and To determine the levels of NO 2 and SO 2 concentrations in ambient air using passive samplers in Chiang Mai city To determine the levels of NO 2 and SO 2 concentrations in ambient air using passive samplers in Chiang Mai city

Preparation of diffusion tubes diffusion tubes – polystyrene (ps), polyethylene (pe), and “Gradko” tubes diffusion tubes – polystyrene (ps), polyethylene (pe), and “Gradko” tubes Sampling medium - Whatman no. 40 filter paper Sampling medium - Whatman no. 40 filter paper Absorbents for NO 2 – TEA and NaOH plus NaI Absorbents for NO 2 – TEA and NaOH plus NaI Absorbents for SO 2 – TEA, Na 2 CO 3, and NaOH Absorbents for SO 2 – TEA, Na 2 CO 3, and NaOH 2. Experimental  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

5.4 cm 1.2 cm1.3 cm TEA coated filter paper Polyethylene cap Polystyrene tube Polyethylene tube Diagram of diffusion tube

Analysis of NO 2 - by spectrophotometer Extraction with DI water Extraction with DI water Color formation with reagent mixture (Sulfanilamide + N-1 naphthyl ethylene diamine hydrochloride solution) Color formation with reagent mixture (Sulfanilamide + N-1 naphthyl ethylene diamine hydrochloride solution) Measured at 540 nm on PerkinElmer Lambda 25 Spectrophotometer Measured at 540 nm on PerkinElmer Lambda 25 Spectrophotometer Analysis of NO 2 - and SO 4 2- 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

3. Results & Discussion PE tubes % > PS tubes Correlation between NO 2 measurements by PS and PE tubes (Analysis by Spectrophotometer)

Correlation between SO 2 measurements from 4 weeks exposure of PS and PE tubes PE tubes % > PS tubes

Correlation between SO 2 measurements from 2 weeks exposure of PS and PE tubes PS tubes % > PE tubes

NO 2 measurements (01/22/2004 – 02/05/2004)

SO 2 measurements (01/22/2004 – 02/19/2004)

Correlation between NO 2 measurements from active and passive sampling for 2 weeks period Underestimation:54.13% PS tubes and 15.39% PE tubes

Detection limits for instrument Spectrophotometer Spectrophotometer – 0.09 g/ml NO 2 - Ion Chromatograph Ion Chromatograph – DL: 0.04 g/ml NO 2 - and 0.02 g/ml SO 4 2- – Minimum Detectable Quantity: 0.48 g.sec NO 2 - and 0.36 g.sec SO 4 2- Detection limits for passive sampling method NO 2: 1.6 g/m 3 for PS and 3.9 g/m 3 for PE tubes NO 2: 1.6 g/m 3 for PS and 3.9 g/m 3 for PE tubes SO 2 (2 weeks) : 1.9 g/m 3 for PS and 1.7 g/m 3 for PE tubes SO 2 (2 weeks) : 1.9 g/m 3 for PS and 1.7 g/m 3 for PE tubes SO 2 (4 weeks) : 1.4 g/m 3 for PS and 2.1 g/m 3 for PE tubes SO 2 (4 weeks) : 1.4 g/m 3 for PS and 2.1 g/m 3 for PE tubes

Diffusion tubes (ps and pe) showed good trends of NO 2 and SO 2 concentrations Diffusion tubes (ps and pe) showed good trends of NO 2 and SO 2 concentrations Good correlation between ps and pe tubes Good correlation between ps and pe tubes Good correlation between active and passive sampling measurements for NO 2 but variable for SO 2 Good correlation between active and passive sampling measurements for NO 2 but variable for SO 2 Underestimation for NO 2 and overestimation for SO 2 by diffusion tubes compared to active sampling; also supported by “Gradko” tubes Underestimation for NO 2 and overestimation for SO 2 by diffusion tubes compared to active sampling; also supported by “Gradko” tubes Variations in blank measurements Variations in blank measurements Precision % for NO 2 and 16.36% for SO 2 Precision % for NO 2 and 16.36% for SO 2 4. Conclusion

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