Insights on Air Pollution During COVID-19: A Review

Air quality improved due to a sudden reduction in the mass concentration of criteria pollutants (PM2.5, PM10, NOx, CO, SO2) except ozone (O-3) over cities of the world during the novel coronavirus diseases (COVID-19) lockdown. Such reduction in pollutants concentration during the lockdown period is an indicator of pollutants contributed from human-induced sources. The elevated ozone level during the lockdown period is explained by shifted NOx-mediated reaction towards volatile organic carbon (VOCs) mediated reaction. The reduction in pollutants concentration and improved air quality is not uniform for outdoor and indoor environments. The indoor air quality is quite poor compared to outdoor throughout the lockdown period. The degradation in indoor air quality is associated with increased human activities and the degree of ventilation inside the home. The number of active COVID-19 cases is associated with air quality over a region. The improved air quality helped in a reduction in COVID-19 virus transmission among the people. Present review articles provide detailed insight into current research progress, the impact of lockdowns on outdoor and indoor air quality in different cities of the world. Further, this review articles provide a detailed overview of an elevated O-3 level during the lockdown period and the mechanism of formation.