Impact on particulate matters in India's most polluted cities due to long-term restriction on anthropogenic activities.

Our purpose of this research is to study the variation in air quality during lockdown (LD) and Post-lockdown (Post-LD) with respect to Pre-lockdown (Pre-LD) in most polluted cities of India by comparing the data of PM and PM in different periods: Pre-LD, LD and post-LD. We have selected top five cities of India out of the 20 most polluted cities across the world including Ghaziabad, Delhi, Noida, Greater Noida, and Lucknow (LKO). Historical data of atmospheric PM and PM for all cities were obtained from the Central Pollution Control Board (CPCB) online web portal of air quality data, except LKO. However, atmospheric PMs was monitored in LKO and samples of PM and PM were collected. During the LD and Post-LD period, due to anthropogenic emissions switch-off' a sharp decline was observed in concentrations of PM and PM in both circumstances (monthly and mean variation) as compared to Pre-LD in all selected cities. The Percentage changes (PCs) was found in mean concentrations of PM and PM during LD** and Post-LD*** with respect to Pre-LD at selected cities; Delhi -40.78%, -58.42%* and -57.60%, -70.11%; Ghaziabad -31.20%, -53.91% and -57.29%, -44.82%; Noida -36.59&, -53.95& and -58.36%, -68.49%; Greater Noida -39.39%, -55.75% and -61.07%, -71.56%; LKO -57.95%, -65.01% and -63.31%, -59.95%* respectively. The PCs of both pollutants exhibited a significant decrease in mean concentrations in all selected cities during LD and Post-LD with respect to Pre-LD period. Consequently, the results of current studies suggest that due to COVID-19 pandemic national LD restriction on anthropogenic activities, both coarse and fine pollutants have significantly reduced and air quality greatly improved during LD and Post-LD as compared to pre-LD period in all selected cities of India.