The COVID-19 pandemic spread all over the world in early 2020. India imposed a nationwide lockdown on March 25, 2020, for more than a month to contain the COVID-19 infection. During the nationwide lockdown, transport, industries, and commercial activities were suspended, except for essential services. We made a detailed analysis of the impacts of COVID-19 on air quality in India by using the data from more than 200 Continuous Ambient Air Quality Monitoring Stations
(CAAQMS) and reported a change in the National Air Quality Index (NAQI), spatial distribution and concentration levels of PM10, PM2.5, CO, NO2, SO2, and O3 from January to April 2020 nationwide and in five major cities, namely, Delhi, Mumbai, Kolkata, Chennai, and Hyderabad. We defined the period between February 25 to March 24, 2020, as ‘before lockdown’ and March 25 to April 30, 2020, as ‘during lockdown’. The NAQI and satellite visual maps of AOD, NO2, CO, and SO2 from January to April 2020 showed a significant decrease in air pollution levels in India. The average concentration levels of PM10, PM2.5, CO, NO2, and SO2 have decreased nationwide by 33, 34, 21, 47, and 21%, respectively, during the nationwide lockdown compared to their concentration levels before the lockdown. While comparing their concentration levels of the nationwide lockdown period with those observed in April 2019 at the same CAAQMS, it was found that the nationwide average concentration levels of PM10, PM2.5, CO, NO2, and SO2 were decreased by 53, 45, 27, 54, and 35%, respectively. The trends of decreasing air pollutants during the lockdown in five major cities were almost the same as nationwide. The concentration levels of O3 have shown an increasing trend from January–April 2020 including during the nationwide lockdown. The COVID-19 has provided a rare opportunity for India for the collection of air pollution baseline data which could be useful in the formulation of air pollution reduction policies in the future.