Improvement in air quality and its impact on land surface temperature in major urban areas across India during the first lockdown of the pandemic

Bikash Ranjan Parida; Somnath Bar; Gareth Roberts; Shyama Prasad Mandal; Arvind Chandra Pandey; Manoj Kumar; Jadunandan Dash

doi:10.1016/j.envres.2021.111280

Improvement in air quality and its impact on land surface temperature in major urban areas across India during the first lockdown of the pandemic

Environ Res. 2021 Aug:199:111280. doi: 10.1016/j.envres.2021.111280. Epub 2021 May 21.

Authors

Bikash Ranjan Parida¹, Somnath Bar², Gareth Roberts³, Shyama Prasad Mandal², Arvind Chandra Pandey², Manoj Kumar⁴, Jadunandan Dash³

Affiliations

¹ Department of Geoinformatics, School of Natural Resource Management, Central University of Jharkhand, Ranchi, 835222, India. Electronic address: bikashrp@gmail.com.
² Department of Geoinformatics, School of Natural Resource Management, Central University of Jharkhand, Ranchi, 835222, India.
³ Geography and Environmental Science, University of Southampton, Highfield, Southampton, SO17 1BJ, United Kingdom.
⁴ Department of Environmental Sciences, School of Natural Resource Management, Central University of Jharkhand, Ranchi, 835222, India.

Abstract

The SARS CoV-2 (COVID-19) pandemic and the enforced lockdown have reduced the use of surface and air transportation. This study investigates the impact of the lockdown restrictions in India on atmospheric composition, using Sentinel-5Ps retrievals of tropospheric NO₂ concentration and ground-station measurements of NO₂ and PM_2.5 between March-May in 2019 and 2020. Detailed analysis of the changes to atmospheric composition are carried out over six major urban areas (i.e. Delhi, Mumbai, Kolkata, Chennai, Bangalore, and Hyderabad) by comparing Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) and land surface temperature (LST) measurements in the lockdown year 2020 and pre-lockdown (2015-2019). Satellite-based data showed that NO₂ concentration reduced by 18% (Kolkata), 29% (Hyderabad), 32-34% (Chennai, Mumbai, and Bangalore), and 43% (Delhi). Surface-based concentrations of NO₂, PM_2.5, and AOD also substantially dropped by 32-74%, 10-42%, and 8-34%, respectively over these major cities during the lockdown period and co-located with the intensity of anthropogenic activity. Only a smaller fraction of the reduction of pollutants was associated with meteorological variability. A substantial negative anomaly was found for LST both in the day (-0.16 °C to -1 °C) and night (-0.63 °C to -2.1 °C) across select all cities, which was also consistent with air temperature measurements. The decreases in LST could be associated with a reduction in pollutants, greenhouse gases and water vapor content. Improvement in air quality with lower urban temperatures due to lockdown may be a temporary effect, but it provides a crucial connection among human activities, air pollution, aerosols, radiative flux, and temperature. The lockdown for a shorter-period showed a significant improvement in environmental quality and provides a strong evidence base for larger scale policy implementation to improve air quality.

Keywords: AOD; Atmospheric pollutants; LST; Net radiative flux; Water vapor.

MeSH terms

Air Pollutants* / analysis
Air Pollution* / analysis
COVID-19*
Cities
Communicable Disease Control
Environmental Monitoring
Humans
India
Pandemics
Particulate Matter / analysis
SARS-CoV-2
Temperature

Substances

Air Pollutants
Particulate Matter