Radiative Impacts of Aerosols During COVID-19 Lockdown Period Over the Indian Region

Abstract

The COVID-19 lockdown restrictions influenced global atmospheric aerosols. We report aerosol variations over India using multiple remote sensing datasets [Moderate Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), Cloud-Aerosol Lidar, and Infrared Pathfinder (CALIPSO)], and model reanalysis [Copernicus Atmosphere Monitoring Service (CAMS)] during the lockdown implemented during the COVID-19 pandemic outbreak period from March 25 to April 14, 2020. Our analysis shows that, during this period, MODIS and CALIPSO showed a 30–40% reduction in aerosol optical depth (AOD) over the Indo-Gangetic Plain (IGP) with respect to decadal climatology (2010–2019). The absorbing aerosol index and dust optical depth measurements also showed a notable reduction over the Indian region, highlighting less emission of anthropogenic dust and also a reduced dust transport from West Asia during the lockdown period. On the contrary, central India showed an ∼12% AOD enhancement. CALIPSO measurements revealed that this increase was due to transported biomass burning aerosols. Analysis of MODIS fire data product and CAMS fire fluxes (black carbon, SO2, organic carbon, and nitrates) showed intense fire activity all over India but densely clustered over central India. Thus, we show that the lockdown restrictions implemented at the government level have significantly improved the air quality over northern India but fires offset its effects over central India. The biomass-burning aerosols formed a layer near 2–4 km (AOD 0.08–0.1) that produced heating at 3–4 K/day and a consequent negative radiative forcing at the surface of ∼−65 W/m2 (±40 W/m2) over the central Indian region.

Erratic Asian summer monsoon 2020: COVID-19 lockdown initiatives possible cause for these episodes?

“…Several other recent studies have also documented considerable reduction in AOD levels (e.g. Kumar 2020 ; Singh and Chauhan 2020 ; Kumari and Toshniwal 2020 ; Bhawar et al 2021 ) Model-based analysis also documents reduced aerosol amount (particularly over southern and eastern Asia) and associated increase in surface shortwave radiation levels due to COVID-19 regulations (e.g. Jones et al 2021 ; Fadnavis et al 2021 ).…”

Interpreting the COVID effect on atmospheric constituents over the Indian region during the lockdown: chemistry, meteorology, and seasonality

“…The wind system showed a major change in northern India and IGP during the first half of March bringing in the transition from winter to pre-monsoon. Also, Bhawar et al ( 2021 ) observed that the transport of dust from West Asia was lower compared to the previous years during the lockdown period, in spring of 2020. This led to the reduction of dust aerosols over the Indian region.…”

Improved Imaging Model in the Presence of Multiplicative Spatially Extended Cloaking Interference

“…As a result, areas of the surface with the same optical properties can have different brightness. For calculations using the Bouguer's formula, it is necessary to know the optical thickness of the atmosphere τ [12][13]. This can be done by measuring the attenuation of solar radiation on Earth.…”

“…From the satellite you can estimate the brightness of objects with a priori known optical characteristics. It is also possible to roughly estimate τ in the visible part of the spectrum using the relationship between τ and the meteorological characteristics of the troposphere -air temperature, wind speed, relative humidity and water vapor pressure [12][13]. Bradley M. and Gasseler M. [12] note that the influence of the atmosphere can be taken into account more accurately on the basis of the theory of radiation transfer in the atmosphere.…”