Variation in Air Quality over Delhi Region: A Comparative Study for 2019 and 2020

Air quality of highly industrialized cities has shown enhanced potential for adverse impacts upon environment and human health. Spread of the COVID-19 in people suffering from some ailment is one of the examples. Meanwhile, complete and partial lockdown were imposed, nationwide, throughout the globe. This study portrays the spatio-temporal variations of atmospheric pollutants over eight regions in National Capital Territory (NCT) Delhi, India, during 2019–2020. It focusses on the entire year with special emphasis on four phases of lockdown and unlock with varying restrictions. As compared to 2019, the results show decrease in relative percent by for fine particulate matters (~ 11.6%), oxides of nitrogen (~ 7%), oxides of sulfur (~ 3.7%), ozone (~ 7.7%), carbon monoxide (~ 20.7%), benzene (~ 11%) and toluene (~ 14%). It was found that strict lockdown phase-I had major contribution to this change. Toluene:Benzene ratios for summer coinciding with strict lockdown confirmed non-operating stationary sources. Later phases were provided with relaxation in certain sectors (mainly vehicular mobility and industrial sector) accompanied with various meteorological impacts, hence did not show much variations. After unlock-IV, anthropogenic activities were found to be accelerated to meet the halted economic demands. Meanwhile, during winter season, biogenic emissions and meteorological factors together affect the air quality in India, aiding air dispersion inhibition due to which the pollutants level showed immediate rise. Restricted human activities prevailing during the lockdown and unlock phases proved to be beneficial in terms of stumping the emission of pollutants into the ambient environment proving that the imposed lockdown healed the environment temporarily.