Assessment of air quality in Kolkata before and after COVID-19 lockdown

Air Pollution plagues urbanised areas and enhances mankind's vulnerability to the COVID-19 virus. According to W.H.O, Kolkata (India) ranks 25(th) amongst 1100 cities in the world. Curbs on traffic movement reduced this pollution during COVID-19 lockdown. Resumption of activities nullified this. This study analyses the trend of air pollutants, their interrelationships with PM2.5, PM10, resultant National Air Quality Indices (NAQIs) before and after COVID-19 lockdowns in Kolkata. Temporal trend analysis, PCA, multiple regressions and NAQIs were computed using pollutant data. SO2, NO2, CO, NH3, PM10 and PM2.5 witnessed drastic rise and fall and again subsequent rise through the pre-lockdown to lockdown and unlock phases, respectively. NAQIs reduced by 74.55%, in the former phase, while in the next it reduced by 5.93%. PM10 and PM2.5, <5 mu m in aerodynamic diameter, had positive associations with SO2 and NO2, which stimulates air-borne transmission of COVID-19. Pollutant monitoring, bio-filtration, biofuel use may be adopted.