A year-round study of ambient gaseous pollutants, their atmospheric chemistry and role in secondary particle formation at an urban site in Delhi

Continuous measurement of the four atmospheric gaseous pollutants (SO2, NO2, CO and O3) were made for a period of about one year (June 2019 to April 2020) at a representative urban site in Delhi. All the four pollutants were found to be elevated during the post-monsoon season (October-December) with peak values observed in the month of November. The present study explores the trends of the atmospheric gas pollutants in a highly polluted atmosphere. In addition, we have highlighted the role of these pollutants in atmospheric chemistry including particle formation and successive growth. During two short-term study periods, a distinct particle growth was observed in the night time associated with the oxidation of SO2 into sulphate particles especially during the post-monsoon season explaining the haze events observed frequently in the city with additional in-fluence of meteorological factors. Unusual high levels of CO observed during pre-monsoon season (March-April) are likely to be associated with the elevated levels of natural biogenic emissions. The present study is one of the best examples validating the conventional secondary chemistry of gaseous pollutants in urban atmosphere.