A brief on intertwined physico-chemical interactions of air pollutants during COVID-19 lockdown

Abstract

This brief presents an intriguing aspect of the physico-chemical interactions among particulate matters (PM_2.5; PM₁₀) and several gases pollutants during pre- (01 March to 24 March 2020) and COVID-19 first phase of lockdown period (25 March to 30 April 2020) over Delhi-National Capital Region. In order to see the impact of lockdown on ambient particulate and gaseous pollutants, we have also compared the results of 2020 with a normal year 2019 and 2021. Results show relatively clean atmosphere (reduced pollutants concentrations except ozone) during lockdown period as compared to pre-lockdown period of 2020. Similar kinds of results are seen for comparison of 2019 and 2020 for lockdown period. Further, we explore the mechanisms enhancing ozone pollution over Delhi during the COVID-19 lockdown period, in contrast with trends in the fine particulate matter (PM_2.5) and precursors of ozone (CO, NO_x). We suggest that lower NO_x has weakened the O₃ chemical sink during the lockdown. Additionally, reduced aerosol loading allowed more incoming solar radiation favouring ozone production as seen by comparing with 2019 and 2021. The results may be important for policy makers to curb pollution in mega cities like Delhi.