A picture of Delhi’s regional air quality during diminished anthropogenic activities in the COVID-19 era

COVID-19 pandemic lockdown was imposed in 2020 and 2021 globally and in India, which created a temporary switch off for various anthropogenic activities, which helped in improving Delhi’s air quality drastically. The present study discusses air pollution reduction during that lockdown period compared to the previous year. The study tries to establish a comparison between various parameters like particulate matter (PM 10 , PM 2.5 ), gaseous pollutants (SO 2 , NO 2 , CO, O 3 ), and meteorological data (WS, WD, RH, AT, SR) during the year 2019 to 2021. The whole monitoring period is divided into four phases (P-I, P-II, P-III, and P-IV) based on stage-wise lockdown implementation. The data are analyzed using the R Studio version 1.3.1093. The PM 10 concentration falls to 46.6% and 19.2% in 2020 and 2021, compared to 2019, and 69% increase in 2021 from 2020. PM 2.5 reduced to 35% and 8.1% in 2020 and 2021, compared to 2019, and a 48% increase in 2021 from 2020. The O 3 concentration shows an increment of about 10% in 2020 and a reduction of 5% in 2021, compared to 2019, and 12%, compared to 2020. The SO 2 and CO reductions lie in between 20 and 35% in 2020 and 2021, compared to 2019. The NO 2 shows around 56% and 32% reduction during 2020 and 2021 compared to 2019 and a 62% increment in 2021 compared to 2020. An absolute lockdown was imposed in 2020, whereas minimal activity or certain restrictions were only imposed in 2021. Such changes in concentration show that anthropogenic sources played a significant role in determining regional air quality in urban areas. The outcomes of the study show the changes that occurred during that period due to phase-wise implementation of lockdown and other unlocking conditions, which may be helpful for policymakers in implementing certain restrictions based on emissions in a planned manner in the future.