Characterizing the air pollution dynamics amidst three COVID-19-induced lockdowns during the first wave (2020), second wave (2021), and third wave (2022) in the Kolkata and Howrah Municipal Corporations, India

This study characterized India's Kolkata and Howrah Municipal Corporations' air quality during three prominent waves of the coronavirus pandemic (25 March–14 April 2020; 15 May–30 May 2021; and 1 January–15 January 2022). The primary aim was to examine the role of these COVID-19 pandemic-induced lockdowns and their stringency and meteorological factors in governing the pollutant concentrations, namely, CO, NH₃, NO₂, O₃, PM₁₀, PM_2.5, SO₂, and monitored by ten automated air pollution monitoring stations (AAMS) of the Central Pollution Control Board (CPCB). A total of 20 days of pollutant data from ten AAMS across four years were analyzed in this study. CO was above the CPCB standard, while PM_2.5 and PM₁₀ varied during all three waves. PM_2.5, PM₁₀, NO₂, SO_2, and O₃ levels were − 44%, − 34%, − 15%, − 48%, and − 51% less during the second wave than the first wave. The third wave witnessed a rise in air pollution levels compared to the second wave, as the stringency of lockdown was relaxed. Air pollution was the highest during the third wave among the three waves. The daily average (24 h) concentrations of PM₁₀, CO, and NO₂ showed a significantly strong positive correlation with PM_2.5. The results indicated that the meteorological conditions played a central role in governing air pollutant concentration. The spatial distribution map portrayed that the pockets of industrial/transport sectors compromised the overall air quality. Policymakers, planners, and decision-makers must note that the results showed that the city's air pollution level can be alleviated by implementing occasional short-term lockdowns.