COVID-19 lockdown was insufficient to bring India's PM2.5 levels below national standards

The COVID-19 pandemic lockdown provided an unprecedented opportunity to examine changes in India's air quality following abrupt reductions in anthropogenic emissions, particularly from transportation, industry, and construction. While many studies reported substantial pollution declines during the lockdown, most focused exclusively on this period, neglecting the subsequent 'unlock' phase, the influence of transboundary pollution, and the need to distinguish between emission-driven and meteorology-driven changes in PM2.5. Our study addresses these gaps by isolating the contributions of meteorological variability and activity restrictions on PM2.5 across the entire lockdown and unlock phases (February 24-June 30, 2020) using a high-resolution modelling framework and satellite-derived PM2.5 data. Through our WRF-Chem modeling study, we found that PM2.5 concentrations decreased by 29% post-lockdown, compared to a 21% decline over the same period in preceding years, with satellite observations showing similar reductions of 31% and 22%, respectively. However, only an additional 8-9% reduction in 2020, beyond the typical interannual variability, was directly attributable to emission controls, while meteorological factors largely influenced the overall decline. The most pronounced PM2.5 decline occurred in the Indo-Gangetic Plain during the unlock phase. Despite the initial improvements, restrictions on transportation, industry, and construction alone were insufficient to bring PM2.5 levels below the National Ambient Air Quality Standards. A key finding is that persistent emissions from the residential sector, which remained largely unaffected during the lockdown, significantly limited the overall reduction in PM2.5. Without targeted interventions to address household emissions, such as promoting cleaner fuels and improving waste management to prevent garbage burning, India will struggle to achieve sustained air quality improvements. Our results emphasize the urgent need for integrated, regionally tailored, long-term strategies that address all major pollution sources to ensure lasting reductions in PM2.5 levels. Implementing comprehensive measures can significantly improve India's air quality, ensuring a healthier and more sustainable environment.