ABSTRACT
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 PM10 and PM2.5 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 PM10 and PM2.5 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 PM10 and PM2.5 were collected. During the LD and Post-LD period, due to anthropogenic emissions switch-off' a sharp decline was observed in concentrations of PM10 and PM2.5 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 PM10 and PM2.5 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.