Significant effect of COVID-19 induced lockdown on air quality of the Indian Metropolitan City Kolkata using Air Quality Index and Health Air Quality Index

Abstract The lockdown, commencing in India from March 23, 2020 to control the escalation of Covid-19 cases, exhibited a positive impact on the air quality. The study attempts to assess the outcome of lockdown on the air quality of Kolkata, India followed by the comparison of six priority pollutants during pre-lockdown, lockdown, and unlock phases. Averaged concentrations of PM10 (72%), PM2.5 (73%), NOx (84%), SO2 (48%), and CO (61%) showed reduction throughout lockdown in comparison with pre-lockdown phase, although no significant reduction was observed in ground-level Ozone. Unlock Phases I and II showed similar concentrations of the pollutants as that in the lockdown period whereas, in unlock Phase-III, the air quality became comparable to that before lockdown. Statistical analysis confirmed that the reduction in air pollution is attributed to atmospheric factors. PCA analysis established significant positive correlation between particulate matters, CO, SO2, and NO x ; however, no significant correlation was observed between NO x and O3. January and December showed the highest load of most of the pollutants. Health risk was evaluated by calculating the Relative risk and Health Air Quality Index, which showed maximum health risk during the pre-lockdown and minimum during lockdown and unlock Phase-II with the highest contributor being PM10. The study outcome manifests a reduction in environmental pollution as a result of controlled anthropogenic activities.