Abstract
Using ground-based and satellite observation along with aerosol reanalysis products, we show a widespread reduction in aerosol loading over the Indian subcontinent during the COVID-19 (COronaVIrus Disease 2019) lockdown. The pre-lockdown and lockdown period considered in the present study is 20th February–20th March 2020 and 24th March–22nd April 2020. In terms of aerosol optical depth (AOD), loading has reduced up to 40% over the most populated region of India. However, the central part of India shows an unexpected increase (~+20%) in AOD. A simultaneous increase (decrease) in mid-tropospheric relative humidity (wind speed (WS) at 850 hPa) by +85 ± 6.0% (–12 ± 3.9%) occurred during the lockdown. It is found that on a daily scale, the mean AOD is positively (negatively) correlated with mid-tropospheric RH (WS) with a statistically significant linear correlation coefficient of 0.53 (−0.43). An increase (decrease) in RH (WS) of 20% (1 m s–1) was observed to increase AOD by 0.10 (0.04). Thus, we hypothesize that during the lockdown, the increased AOD over central India was due to increased atmospheric moisture coupled with stagnant circulation condition.
Highlights
OPEN ACCESSReceived: July 30, 2020 Revised: October 12, 2020 Accepted: November 11, 2020Publisher: Taiwan Association for Aerosol Research ISSN: 1680-8584 print ISSN: 2071-1409 onlineCopyright: The Author(s)
In order to quantify the impact of lockdown on the aerosol loading, we have chosen two periods; pre-lockdown (20th February–20th March 2020) and during lockdown (24th March–22nd April 2020)
North India, especially the Indo Gangetic Plain (IGP), shows a slight decrease that may be a result of enhanced wind speed as a transition from winter to summer
Summary
Publisher: Taiwan Association for Aerosol Research ISSN: 1680-8584 print ISSN: 2071-1409 online. The total death toll of 484,249 and the number of reported cases reached 9,473,214 (as of 26th June 2020) (WHO, 2020) This pandemic caused an unprecedented response from the countries leading to a complete or partial shutdown of human activities. Majority of the studies related to lockdown induced reduction in air-pollutant focussed over China. Indian region shows a significant reduction in these air-pollutants Despite an overwhelming reduction of major air-pollutants, several regions show an increase in surface PM2.5 concentration, O3 (ozone) level, aerosol loading, and hazy sky (Le et al, 2020; Li et al, 2020; Sicard et al, 2020). We attempt to explain the observed spatio-temporal variability of aerosol over India during the lockdown, using ground-based and space-borne aerosol observations along with aerosol and meteorological reanalysis data
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