Spatial and temporal variations of air pollution over 41 cities of India during the COVID-19 lockdown period

In this study, we characterize the impacts of COVID-19 on air pollution using NO₂ and Aerosol Optical Depth (AOD) from TROPOMI and MODIS satellite datasets for 41 cities in India. Specifically, our results suggested a 13% NO₂ reduction during the lockdown (March 25-May 3rd, 2020) compared to the pre-lockdown (January 1st-March 24th, 2020) period. Also, a 19% reduction in NO₂ was observed during the 2020-lockdown as compared to the same period during 2019. The top cities where NO₂ reduction occurred were New Delhi (61.74%), Delhi (60.37%), Bangalore (48.25%), Ahmedabad (46.20%), Nagpur (46.13%), Gandhinagar (45.64) and Mumbai (43.08%) with less reduction in coastal cities. The temporal analysis revealed a progressive decrease in NO₂ for all seven cities during the 2020 lockdown period. Results also suggested spatial differences, i.e., as the distance from the city center increased, the NO₂ levels decreased exponentially. In contrast, to the decreased NO₂ observed for most of the cities, we observed an increase in NO₂ for cities in Northeast India during the 2020 lockdown period and attribute it to vegetation fires. The NO₂ temporal patterns matched the AOD signal; however, the correlations were poor. Overall, our results highlight COVID-19 impacts on NO₂, and the results can inform pollution mitigation efforts across different cities of India.