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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 PM 2.5,  PM 10 , 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. SO 2 , NO 2 , CO, NH 3 , PM 10  and PM 2.5  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%. PM 10  and PM 2.5 , &lt;5µm in aerodynamic diameter, had positive associations with SO 2  and NO 2 , which stimulates air-borne transmission of COVID-19. Pollutant monitoring, bio-filtration, biofuel use may be adopted.

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