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.
Highlights
There are growing concerns about aerosol pollution over the Indian region due to the negative effects they produce on health and the hydrological cycle (Meehl et al, 2013; Vinoj et al, 2014; D’Errico et al, 2015; Fadnavis et al, 2017a; Fadnavis et al, 2019a)
Trajectory analysis-based studies show that anthropogenic aerosols over the Bay of Bengal are associated with transport from the Indian region (Nair et al, 2016)
We understand the influence of dust transport from West Asia on the Indian region which occurs in spring (Lau and Kim 2006), here we show the changes in dust during the lockdown period using CALIPSO measurements of dust optical depth and the Ozone Monitoring Instrument (OMI) aerosol index (OMI-Absorbing Aerosol Index (AAI))
Summary
There are growing concerns about aerosol pollution over the Indian region due to the negative effects they produce on health and the hydrological cycle (Meehl et al, 2013; Vinoj et al, 2014; D’Errico et al, 2015; Fadnavis et al, 2017a; Fadnavis et al, 2019a). Aerosol pollution over India has increased hazy days at a rate of 2.6 days per year (Thomas et al, 2019). Aerosol Radiative Forcing over India (ARFI) net observations show the rate of increase at 2.3% per year in aerosol loading over India (Krishna Moorthy et al, 2013). Agricultural fires and crop residue activity during winter/spring cause a substantial increase (43%) in aerosol loading over North India (Jethva et al, 2019; Fadnavis et al, 2021). We report how the aerosol vertical distribution impacted the heating rates and radiative forcing over India during the lockdown period of March 25–April 14, 2020.
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