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

Abstract

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–NO_X–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–NO_X–O₃ shows that ozone generation across Delhi primarily lies in the VOC-sensitive regime (VOCs/NO_X < 8). A decrease in VOCs/NO_X values associated with an increase in surface ozone resulted from the lower values of NO_X. 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 (PM_2.5 and PM₁₀) across Delhi. This counterintuitively leads to enhanced air pollution despite the improvement in air quality during the lockdown period.