Impact of COVID-19 Control Measures on Trace Gases (NO2, HCHO and SO2) and Aerosols over India during Pre-monsoon of 2020

Abstract

To prevent the transmission of COVID-19, India implemented country-wide restrictions on socioeconomic activities. Using satellite observations for the pre-monsoon (March-April-May) season, we explore the effect of the extended lockdown, on nitrogen dioxide (NO2), formaldehyde (HCHO), sulfur dioxide (SO2) and aerosol optical depth (AOD) over India. In this present study we evaluate and quantify the changes in pollutants across six different geographical zones along with the six most populous cities in the country. During April-May the lockdown have resulted in a net decrease in NO2 column density over India in 2020 compared to 2017-2019 average for the same months. Maximum average seasonal reduction of both NO2 (-5.6%) and HCHO (-1.3%) occured over southern India (SI). Compared to March and April, anomalous HCHO for all the regions decreased in May. Anomalous surface cooling induced lower volatile organic carbons (VOCs) emission and slower VOC oxidation due to absence of high nitric oxide led to decrease in HCHO. A reduction in NO2 was also seen over the top six populous Indian cities, with Mumbai recording the highest decrease (-33.7%). But only Chennai showed a substantial decrease (-6.8%) in HCHO. A significant seasonal reduction in SO2 was noted over western India (WI) and SI. Additionally, widespread decline covering all the zones was found in the pre-monsoon AOD. In April, the decrease occurred primarily over the Indo-Gangetic-Plains (IGP) and eastern India, while in May a marked homogeneous reduction was noted over entire India. Aerosol induced attenuation of incident solar radiation leads to concurrent changes in MERRA2 insolation during pre-monsoon of 2020. Furthermore, reduced anthropogenic aerosols resulted in reduction of avaible cloud condensation nuclei (CCN) leading to larger cloud droplet size and hence increased precipitation during pre-monsoon, 2020.

The Impact of COVID-19 Lockdowns on Air Quality—A Global Review

“…Mumbai recorded the highest decrease of NO 2 (34%) with a seasonal decrease of SO 2 in western and southern India [48].…”

Short-term impacts of air pollutants in three megacities of India during COVID-19 lockdown

“…PM 10 , PM 2.5 , CO, NO 2 ), attributed to the decline in anthropogenic activities particularly vehicular and industrial (Kumar et al 2020 ; Mahato et al 2020 ; Sharma et al, 2020 ). Biswas and Ayantika ( 2020 ) used satellite data to explore the effect of lockdown on NO 2 , formaldehyde (HCHO), SO 2 and AOD over India and showed large-scale decrease in all the measured parameters spanning almost the entire Indian landmass. Further, Sharma et al ( 2020 ) used a WRF-AERMOD model to highlight an overall decline of 43, 31, 10 and 18% in levels of PM 2.5 , PM 10 , CO, and NO 2 during the lockdown period in comparison to similar period in previous years.…”

Global Surface HCHO Distribution Derived from Satellite Observations with Neural Networks Technique

“…However, most satellite-based retrieval can only provide the total column concentration due to their limitations in vertical resolution. Therefore, most studies on ambient HCHO only focus on the total amount in the vertical column in certain regions, such as North America [19], South America [20], Europe [21], Asia [22,23] and Africa [7], instead of focusing on surface concentration.…”