Study of Air Quality over Delhi during COVID-19 Lockdown Based on Remote Sensing Observations

Increasing concentrations of toxic pollutants and particulate matter are a major concern related to human health. The present work is structured into two phases; the first is aimed at understanding the O3–NOX–VOC sensitivity over Delhi during the lockdown period; the second phase examines the influence of dust-induced aerosol particles on air pollution during the lockdown period using satellite-derived and ground-based observations. The analysis of VOC–NOX–O3 shows that ozone generation across Delhi primarily lies in the VOC-sensitive regime (VOCs/NOX < 8). A decrease in VOCs/NOX values associated with an increase in surface ozone resulted from the lower values of NOX. Apart from ozone precursors (NOx and VOCs), meteorological variables also play a vital role in the generation of surface ozone. The two-way ANOVA test and partial correlation analysis show the surface temperature to be a dominant factor which limits surface ozone across Delhi. Dust-induced high aerosol loading (aerosol optical depth values of ~0.7 to 0.9) is observed during the first and last weeks of April. The presence of a shallow atmosphere and increased dust-induced aerosol particles peculiarly increase the content of particulate matter (PM2.5 and PM10) across Delhi. This counterintuitively leads to enhanced air pollution despite the improvement in air quality during the lockdown period.