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|Development of Low Cost Passive Sampling Diffusion Tubes for Spatial Monitoring of NO 2, SO 2 and 0 2 In Kathmandu Valley
|Byanju, Rejina Maskey
|Nitrogen dioxide;Sulphur dioxide
|Faculty of Chemistry
|Central Department of Chemistry
|The work embodied in this research was to find out the solution for the difficulties often encountered by the resource limited countries in using high cost automatic instruments for air pollution monitoring and assessment. Monitoring and assessment is an important aspect in the protection of the public from the air -pollution –induced- health- hazard by improving exposure assessment and formulating mitigations. The overall goal of this study was to develop low cost passive samplers logistically feasible and technically suitable to use for ambient NO 2 , SO 2 and O 3 monitoring in Kathmandu. Locally available polyethylene tubes were developed as diffusion tubes for ambient passive sampling. These tools were then applied to assess the spatial variability in NO 2 , SO 2 and O 3 across the Kathmandu valley The passive measurements include development of these tubes into diffusive tubes using triethanolamine (TEA) for NO 2 , SO 2 and nitrite- coated filter (GF/A filter paper) for O absorbent bases. After extraction with water, modified Griese-Saltzmann method and West- Gaeke method were used for analysis of nitrite and sulphate adduct formed due to reaction of NO 2 and SO 2 respectively . Azide modified sodium salicylate method was used for analysis of nitrate formed by the oxidation of nitrite by ozone from the air using uv visible spectrophotometer. The results were compared with ferm- badge type passive samplers from IVL-Sweden and other active methods. The detection limits of the passive sampling methods were found to be suitable for use in tested environment. The instrumental detection limits obtained from calibration curve were 0.09 µg/ml and 0.05μg/ml for NO in the range of 1.75 to 2.73 μg/m tested exposure periods. 2 – and SO 3 4 2, respectively. The detection limits of NO ; and that for SO 2 were 1.12 to 5.85μg/m Precision of the method as expressed as coefficient of variation was good enough for the monitoring of NO 2 SO 2 and O 3 viii 3 . 2 3 as were for different in ambient air of Kathmandu. The method showed strong correlation with high volume sampler and no significant difference with ferm badge –IVL samplers at p=0.05. Precision of the passive sampling method for measurement expressed as coefficient of variation (CV) was 13.3% with an overall range of 2.3-20.8% for NO 2 and it was 14.5% with an overall range of 3.4-20.2%. The results of all the exposure analysis provided a reliable ambient O 3 sampling with good precision. Precision of O 3 measurements were found to be in the range of 0.1 to 14%. The prepared diffusion tubes were suitable for 24 hour sampling in the tested environments. The tested method overestimates of 22.77% and 7.9% in compare to that of automated ozone analyzer and Ferm-IVL sampler respectively. The result was acceptable according to US National Institute of Safety and Health (Seethapathy et al., 2007) The limit of detection for developed passive sampling method was 0.011 µg/ m suitable to measure O 3 in the study area . The passive monitoring and the assessment of the quality of air prevailing in the urban Kathmandu revealed that all the three pollutants monitored NO in winter dry season were higher than in rainy season. NO 2 2 , SO and SO 2 and O 2 ix 3 3 , which was concentrations were below National Ambient Air Quality Standard (NAAQS) for both the monitoring period however, NO several points exceeded the NAAQS. Higher concentrations of NO high traffic density areas. Transportation was the major source of NO 2 were observed at the 2 pollution in the city other hand was related with the industrial emission especially due to the brick kilns and hotels. The O average of 47 µg /m 3 3 concentrations varied between 25 and 100 µg /m in the city. SO . The maximum was observed from rural site Matsygaun while minimum observed from Baudha. The pre-monsoon months specially March –May was the most vulnerable period for high concentration ozone exposure in Kathmandu valley. Key words: Diffusive, Passive sampler, Nitrogen dioxide, Sulphur dioxide, Ozone.
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