International Journal of Environment and Climate Change

The COVID-19 lockdown in India created a unique opportunity to examine how abrupt reductions in anthropogenic activity influence atmospheric composition at regional scales. This study evaluates changes in aerosol optical depth (AOD), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and ozone using MODIS, OMI, and MERRA-2 datasets for March–June 2020 relative to the 2014–2019 climatology. Results show substantial improvements in air quality, with markedly reduced AOD and trace-gas concentrations across the Indo-Gangetic Plain (IGP), Western India, and major urban–industrial corridors. Reductions were particularly pronounced in the IGP, where NO₂ and SO₂ decreased sharply, and AOD declined despite seasonal dust influences. In contrast, parts of Central India exhibited localized enhancements driven by meteorological factors, underscoring the role of wind speed, humidity, and boundary-layer dynamics in shaping pollutant distribution.

Ozone displayed contrasting behavior: tropospheric ozone decreased, reflecting reduced precursor emissions, while total column ozone increased slightly, likely due to changes in photochemistry under low-NOₓ conditions and favorable stratospheric–tropospheric interactions. This distinction highlights the complex, non-linear nature of ozone chemistry during periods of reduced emissions.

Overall, the findings reveal strong regional variability in atmospheric responses to emission reductions, demonstrating that meteorology can modulate or even override expected pollutant declines. The study provides valuable insights for designing region-specific and meteorology-aware air quality management strategies, and illustrates how emission control interventions may yield rapid but spatially heterogeneous improvements in atmospheric composition across India.