Simultaneous long-term measurements of near-surface air pollutants at an urban station, New Delhi, were studied during 2005-2012 to understand their distribution on different temporal scales. The annual mean mass concentrations of nitrogen dioxide (NO 2), sulphur dioxide (SO 2), particulate matter less than 10 µm (PM 10) and suspended particulate matter (SPM) were found to be 62.0 ± 27.6, 12.5 ± 8.2, 253.7 ± 134 and 529.2 ± 213.1 µg/m 3 , respectively. The 24-hr mean mass concentrations of NO 2 , PM 10 and SPM were exceeded on ∼27%, 87% and 99% days that of total available measurement days to their respective National Ambient Air Quality Standard (NAAQS) level. However, it never exceeded for SO 2 , which could be attributed to reduction of sulphur in diesel, use of cleaner fuels such as compressed natural gas, LPG, etc. The mean mass concentrations of measured air pollutants were found to be the highest during the winter/post-monsoon seasons, which are of concern for both climate and human health. The annual mean mass concentrations of NO 2 , PM 10 and SPM showed an increasing trend while SO 2 appears to be decreasing since 2008. Air mass cluster analysis showed that north-northwest trajectories accounted for the highest mass concentrations of air pollutants (more prominent in the winter/post-monsoon season); however, the lowest were associated with the southeast trajectory cluster.

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