COVID-19 Lock-down in Delhi: Understanding Trends of Particulate Matter in Context of Land-Use Patterns, GIS Mapping, and Meteorological Traits.

The effectiveness and cost implications are always top factors for policy makers while deciding upon the appropriate air pollution abatement measures. The present study aimed to understand the actual particulate matter (PM_2.5 and PM₁₀) patterns during different phases of COVID-19 lockdown periods and depict their spatial distributions covering the 36 major areas in Delhi, India. Drastic visible reduction in both the pollutants was found during lockdown phase 1 and 2. Average PM_2.5 reductions of 41.97%, 39.24%, 56.04%, and 56.77% were recorded comparing lockdown and/or study period with the years 2018, 2019, 2021, and 2022, respectively. Similar average reduction of PM₁₀ to the magnitude of 51.72%, 48.95%, 48.24%, and 49.00% was found for the referred years. However, the reduction during the before-lockdown period of 2018 and 2019 and the year 2020 did not follow such radical reduction returning the values for PM_2.5 as 7.66–14.88% and that for PM₁₀ as 12.86–20.67%. The geospatial maps generated for Delhi city followed the similar findings at macro level depicting huge reduction in PM distribution classes for the study period. For instance, the percent surface area under "moderately high" polluted due to PM_2.5 came down to 0.61 during lockdown phase 2 from 13.96 during January 2020. Further, about 15 of the 36 locations reported compliance to the National Ambient Air Quality Standards (NAAQS) for either of the pollutants during the study period. Nevertheless, such reductions are short-lived because the levels went up again in the years 2021 and 2022 (except similar lockdowns) as the situation got back to normal daily life activities postlockdown. Although, lockdown may be imposed in case of severe ambient air quality in a densely populated megacity like Delhi, it remains a temporary or quick-fix solution, to be looked as a last line of defense. [ABSTRACT FROM AUTHOR]