Effect of COVID-19 Lockdown on the Spatio-temporal Distribution of Nitrogen Dioxide Over India

The nationwide lockdown was implemented in India from 25 March 2020 onwards to control the spread of deadly Coronavirus disease 2019 (COVID-19). A sudden shutdown of anthropogenic activities resulted in abrupt decrease of nitrogen dioxide (NO₂) across the Indian region. OMI (Ozone Monitoring Instrument) tropospheric column NO₂ observations show significantly decreased values during 2020 compared to previous years during 25 March to 19 April. The spatiotemporal variation of tropospheric column NO₂ difference between 2020 and average 2017–2019 shows reduction by more than 1 × 10¹⁵ molecules/cm² over the Indo Gangetic Plain, eastern and southern India due to lockdown. However, the western Indian region shows slight enhancement which may be attributed to combined effect of transport of polluted air from Middle East and Pakistan, and relatively higher biomass burning activity during 2020. A significant reduction is also observed on the surface distribution of NO_x (NO + NO₂) over different Indian cities due to COVID-19 lockdown. Maximum reduction in daily average surface NO_x is observed over Kolkata (65.2 ± 18.7 ppbv to 30.3 ± 4.6 ppbv) followed by New Delhi (38.8 ± 17.5 ppbv to 11.5 ± 2.9 ppbv) which may be attributed to vehicle fleet, type of fuel used, power plants and industrial emissions.