Investigation of Changes in Atmospheric Pollutants due to the Cessation of Anthropogenic Activities: Spatial Heterogeneity and Complex Atmospheric Chemistry

Abstract

The current study examines the air quality trends in response to Covid-19-induced lockdowns at various locations in Delhi. The primary pollutants like NO₂, CO, and PM₁₀ have shown reductions during the lockdown phase, but the magnitude varied significantly in different places. Also, during the lockdown, air quality in some areas of Delhi exceeded National Ambient Air Quality Standards. Secondary pollutants like O₃ have shown mixed trends due to complex atmospheric processes and dependence on relative proportions of VOC and NO_x levels. A total of six sites, including traffic, industrial, and residential sites, have been studied. The diurnal behavior of pollutants also differed significantly around different places. During the lockdown, Ashok Vihar, a traffic-influenced area, showed a decrease in O₃ (~ 40%), while at DTU (Traffic site), O₃ levels increased (~ 48%)_. The industrial sites Okhla and Wazirpur also showed different trends during the lockdown; O₃ in Wazirpur decreased by 50%, whereas Okhla increased by 25%. NO_x concentration was lesser in 2020 at all the stations compared to 2019, indicating the positive impact of the lockdown on air pollution due to vehicular emissions. The Approximate Envelope Method estimates the secondary fraction of PM_2.5. This fraction of PM is dominated in the lockdown year in the residential site, while it remains unchanged in the traffic site and increased by 11% in the industrial area. Despite being not so far from each other, these sites show very different patterns of pollutants during lockdown episodes.