Development of Low Cost Passive Sampling Diffusion Tubes for Spatial Monitoring of NO 2, SO 2 and 0 2 In Kathmandu Valley
Date
2012
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Faculty of Chemistry
Abstract
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.
Description
Keywords
Nitrogen dioxide, Sulphur dioxide