The aim of present study was to compare the air quality before and during lockdown due to COVID-19 pandemic at selected metro cities of India (Delhi, Kolkata, Bangalore, and Mumbai). The data of the selected parameters (Particulate Matter having diameter equal to or less than 2.5micron (PM2.5), Particulate Matter having diameter equal to or less than 10micron (PM10), Nitrogen oxides (NO2), Ammonia (NH3), Sulphur oxides (SO2) Carbon monoxides (CO), and Ozone (O3) for the present study was collected from the official website of Central pollution Control Board (CPCB) and analyzed by calculating mean, standard deviation, total variance, and correlation coefficient. Dendrogram analysis was also performed site wise. The concentration of all the parameters except ozone was found highest at Delhi among all the sites. Ozone values were found highest at Bangalore. A strong correlation was observed between PM10 and PM2.5 at all the sites during the study period. A great change in the values of all the studied parameters was observed before and during the lockdown periods. In metro cities values of PM2.5 was found higher than PM10 except at Bangalore where values of PM2.5 was found lower than PM10. Among all the studied metro cities, Delhi was found highly polluted before and during the lockdown period while Bangalore was found least polluted.
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