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

U C Dumka; D G Kaskaoutis; Shubha Verma; Shantikumar S Ningombam; Sarvan Kumar; Sanhita Ghosh

doi:10.1016/j.apr.2020.11.005

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

Atmos Pollut Res. 2021 Feb;12(2):225-242. doi: 10.1016/j.apr.2020.11.005. Epub 2020 Nov 11.

Authors

U C Dumka¹, D G Kaskaoutis^{2

3}, Shubha Verma⁴, Shantikumar S Ningombam⁵, Sarvan Kumar⁶, Sanhita Ghosh⁷

Affiliations

¹ Aryabhatta Research Institute of Observational Sciences, Nainital, 263001, India.
² Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Palaia Penteli, 15236, Athens, Greece.
³ Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, 71003, Crete, Greece.
⁴ Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302, India.
⁵ Indian Institute of Astrophysics, Bangalore, 560034, India.
⁶ Department of Earth and Planetary Sciences, Prof. Rajendra Singh (Rajju Bhaiya) Institute of Physical Sciences for Study and Research, Veer Bahadur Singh Purvanchal University, Jaunpur, 222003, Uttar Pradesh, India.
⁷ Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302, India.

Abstract

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 (NO_x, SO₂, CO, NH₃, and O₃) 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%), PM_2.5 (-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 O₃ (+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 (NO_x, CO and road-dust PM). The WRF-CHIMERE model simulations reveal a remarkable reduction in PM_2.5, 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 PM_2.5 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.

Keywords: Aerosols; Air pollutants; COVID-19; Delhi-NCR; Ground measurements; Remote sensing; WRF-CHIMERE.