Silver Linings In The Dark Clouds Of Covid-19: Improvement Of Air Quality Over India And Delhi Metropolitan Area From Measurements And Wrf-Chimere Model Simulations

The current study examines the impact of the COVID-19 lockdown (25th March until May 17, 2020) period in particulate matter (PM) concentrations and air pollutants (NOx, SO2, CO, NH3, and O-3) at 63 stations located at Delhi, Uttar Pradesh and Haryana states within the Delhi-NCR, India. Large average reductions are recorded between the stations in each state such as PM10 (46 to 58%), PM2.5 (49 to 55%), NO2 (27 to 58%), NO (-54% to -59%), CO (-4 to -44%), NH3 (-2 to -38%), while a slight increase is observed for O-3 (+4 to +6%) during the lockdown period compared to same periods in previous years. Furthermore, PM and air pollutants are significantly reduced during lockdown compared to the respective period in previous years, while a significant increase in pollution levels is observed after the re-opening of economy. The meteorological changes were rather marginal between the examined periods in order to justify such large reductions in pollution levels, which are mostly attributed to traffic-related pollutants (NOx, CO and road-dust PM). The WRF-CHIMERE model simulations reveal a remarkable reduction in PM2.5, NO2 and SO2 levels over whole Indian subcontinent and mostly over urban areas, due to limitation in emissions from the traffic and industrial sectors. A PM2.5 reduction of -48% was simulated in Delhi in great consistency with measurements, rendering the model as a powerful tool for simulations of lower pollution levels during lockdown period.