Assessment of near-surface air pollutants at an urban station over the central Indo-Gangetic Basin: Role of pollution transport pathways

Abstract

The assessment of near-surface air pollutants has been done at an urban site, Varanasi, in the central Indo-Gangetic Basin (IGB) during July 2014 to June 2018. The various pollutants, such as particulate matters of diameter less than 2.5 μm (PM2.5) and less than 10 μm (PM10), sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3) were obtained from the Central Pollution Control Board (CPCB). The annual mean mass concentrations of PM10, PM2.5, SO2, NO2 and O3 were 239 ± 128, 123 ± 89, 17.5 ± 9.6, 52 ± 35 and 30 ± 14 μg m−3, respectively. The concentrations of PM10, PM2.5 and NO2 were found to be higher than their National Ambient Air Quality Standards (NAAQS) by a factor of 4, 3.1 and 1.3, respectively; however, SO2 and O3 were always well within their standard limits. Seasonally, all the pollutants, except ozone were found to be the highest during the postmonsoon and winter seasons. The sources of pollutants have been widely characterized at this site and in general over the IGB. Further, an attempt has been made, for the first time, to elucidate the possible transport pathways of the measured pollutants, especially PM2.5 to downwind of the station using concentration weight trajectory (CWT) analyses with the forward air mass trajectories. The results show significant potential for transport of PM2.5 (~ 65%) from the IGB to downwind over the northern Bay of Bengal region, with more pronounced during the winter season (~ 95%). These results underline the importance of IGB pollution outflow towards downwind continental and marine regions, which can have significant climatic impacts.