The present study focuses on the impact of early imposed lockdowns and following unlocking phases on the status of air quality in six Tier-I and nine Tier-II cities of India as compared to the pre-lockdown measures. Furthermore, the study highlights the possible correlation of air quality index (AQI) with the initial trend of COVID-19 issues including the vaccination cases. Based on the statistical data analysis, we observed that the long-term averages for representing the short-term pre-lockdown conditions can impose a healing effect to the observed anomalies in air pollution data. However, the reduction in air pollution during the imposed lockdown series was only a phenomenal consequence, and the trends started reversing during the later phases of partial unlocking, where the correlation showed reversing trends. Being a yearly averaged parameter, the marginal reductions in the exceedance factor (EF) alone could not dictate air quality compared to the AQI. As there is incoherent variability in the pollutant distributions among the cities during various phases of the study, the trend analysis served as a preferable criterion to choose the preferred sources of variations. Based on the results, the correlation analysis revealed that air quality expressed in terms of AQI can act as an important precursor to estimate the critical phase of COVID-19 spread and the effectiveness of various control measures taken during each phase. Based on our proposed ranking, Kolkata and Patna are ranked first in the Tier-I and Tier-II cities respectively according to their responsiveness to the various institutionalized restrictions in terms of air quality parameters.

An unexpected closure episode of most of the public movement and industrial activities during the initial spreading duration of COVID-19 has significantly resulted in drastic reduction of environmental pollution in the urban areas globally. Being an active bio-aerosol with pandemic effect, COVID-19 presents a never-before scenario for the meteorologists and environmental engineers to look for systematic analysis of the overlap of air quality modelling with modifications in the atmospheric science. The long-term monitoring of pollution records help in defining unique indices for categorizing the severity of the existing pollution and thus helps in developing strategies for improving environmental quality. In this study, we present the observations in major air quality parameters in selected major cities of India using air quality index (AQI) before and after the announcement of a nationwide lockdown that extended nearly for many months. The results indicate a major sustaining type of decline in the average AQI values for major Type-1 and Type-2 cities due to the reduction in public movement and industrial activities, whereas the reduction AQI values for Type-3 and Type-4 cities were observed to be fluctuating due to the continued small-scale industrial activities and low level of awareness about ban on public gathering programmes.