Nationwide CoViD-19 lockdown impact on air quality in India

Abstract

This paper discusses the comparative results of surface and satellite measurements made during the Phase1 (25 March to 14 April), Phase2 (15 April to 3 May) and Phase3 (3 May to 17May) of Covid-19 imposed lockdown periods of 2020 and those of the same locations and periods during 2019 over India. These comparative analyses are performed for Indian states and Tier 1 megacities where economic activities have been severely affected with the nationwide lockdown. The focus is on changes in the surface concentration of sulfur dioxide (SO₂), carbon monoxide (CO), PM_2.5 and PM₁₀, Ozone (O₃), Nitrogen dioxide (NO₂)  and retrieved columnar NO₂ from TROPOMI and Aerosol Optical Depth (AOD) from MODIS satellite. Surface concentrations of PM_2.5 were reduced by 30.59%, 31.64%  and 37.06%, PM₁₀ by 40.64%, 44.95% and 46.58%, SO₂ by 16.73%, 12.13% and 6.71%, columnar NO₂ by 46.34%, 45.82% and 39.58% and CO by 45.08%, 41.51% and 60.45% during lockdown periods of Phase1, Phase2 and Phase3 respectively as compared to those of 2019 periods over India. During 1^st phase of lockdown, model simulated PM_2.5 shows overestimations to those of observed PM_2.5 mass concentrations. The model underestimates the PM_2.5 to those of without reduction before lockdown and 1^st phase of lockdown periods. The reduction in emissions of PM_2.5, PM₁₀, CO and columnar NO₂ are discussed with the surface transportation mobility maps during the study periods. Reduction in the emissions based on the observed reduction in the surface mobility data, the model showed excellent skills in capturing the observed PM2.5 concentrations. Nevertheless, during the 1^st & 3^rd phases of lockdown periods AOD reduced by 5 to 40%. Surface O₃ was increased by 1.52% and 5.91% during 1^st and 3^rd Phases of lockdown periods respectively, while decreased by -8.29% during 2^nd Phase of lockdown period.