Comprehensive assessment of air quality dynamics in Delhi: A tri-phased analysis spanning pre, during, and post-lockdown periods

To mitigate the spread of the global COVID-19 pandemic, various regions, including India, implemented stringent measures such as nationwide lockdowns to curb the spread of the virus. The air quality dynamics during the COVID-19 lockdown period revealed diverse trends across various pollutants all over the world. This study explores the impact of these lockdowns on air quality in Delhi, one of India’s megacities, across distinct phases: pre-lockdown, during lockdown, and post-lockdown periods. PM 10 was observed to show a substantial decline in concentration, particularly in April 2020, serving as a testament to the immediate effectiveness of implementing lockdown measures to control particulate matter concentrations. However, these levels returned to their previous peak in subsequent years post lockdown. PM 2.5 followed a similar pattern, experiencing an initial decline during the lockdown, but as industries and factories resumed their activities post June 2020, the levels shot up back to their original baseline, highlighting the transient nature of low PM concentrations. Other pollutants like Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), and Carbon Monoxide (CO) levels showed varying degrees of mild to steep decline during the lockdown, but they too returned to their original concentrations as few months after the lockdown was lifted. There was, contrary to expectations, an increase in ozone (O3) concentrations after the implementation of lockdown, challenging our assumptions. Spatial mapping was done to observe the variation of concentration in different tehsils of Delhi.