Impact of reduced anthropogenic emissions during COVID-19 on air quality in India.

To mitigate the impacts of the pandemic of coronavirus disease 2019 (COVID-19), the Indian government implemented lockdown measures on 24 March 2020, which prohibited unnecessary anthropogenic activities, thus leading to a significant reduction in emissions. To investigate the impacts of this lockdown measure on air quality in India, we used the Community Multi-Scale Air Quality (CMAQ) model to estimate the changes of key air pollutants. From pre-lockdown to lockdown periods, improved air quality is observed in India, indicated by the lower key pollutant levels such as PM 2.5 (- 26 %), maximum daily 8 h average ozone (MDA8 O 3) (- 11 %), NO 2 (- 50 %), and SO 2 (- 14 %). In addition, changes in these pollutants show distinct spatial variations with the more important decrease in northern and western India. During the lockdown, our results illustrate that such emission reductions play a positive role in the improvement of air quality. Significant reductions of PM 2.5 concentration and its major components are predicted, especially for secondary inorganic aerosols that are up to 92 %, 57 %, and 79 % for nitrate (NO 3-), sulfate (SO 42-), and ammonium (NH 4+), respectively. On average, the MDA8 O 3 also decreases 15 % during the lockdown period although it increases slightly in some VOC-limited urban locations, which is mainly due to the more significant reduction of NO x than VOCs. More aggressive and localized emission control strategies should be implemented in India to mitigate air pollution in the future. [ABSTRACT FROM AUTHOR]