Effect of Lockdown on Pollutant Levels in the Delhi Megacity: Role of Local Emission Sources and Chemical Lifetimes

Abstract

The COVID-19 pandemic resulted in changed emission regimes all over the world. India also imposed complete lockdown on all modes of travel and industrial activities for about 2 months from 25-March-2020 and later unlocked these activities in a phased manner. Here, we study signatures of emissions changes on levels of atmospheric trace gases and aerosols contributing to air pollution over multiple sites in India’s capital Delhi covering various lockdown and unlock phases using satellite data and in-situ observations. The resulting changes in the levels of these species were compared with respect to their average of 2015–2019 to attribute for year to year and seasonal changes. A clear impact of lockdown was observed for AOD, PM, NO2, CO, and SO2 as a result of emission changes, while changed precursor levels led to a change in O3 chemical regimes impacting its concentrations. A detailed analysis of FLEXPART trajectories revealed increased PM levels over Delhi in north-westerly air masses sourced to Punjab region all the way up to Pakistan. Changes in aerosols and NO2 were not only restricted to the surface but transcended the total tropospheric column. The maximum decrease in PM, NO2, CO, and SO2 was observed during the month of total lockdown in April. The lockdown impact varied with species e.g., PM10 and PM2.5 as well as locations even within the periphery of Delhi. While surface level aerosols and NO2 showed significant and almost similar changes, AOD showed much lower decrease than tropospheric column NO2.

Atmospheric Boundary Layer Over Ahmedabad, Western Indian Region: Impact of COVID-19 Nationwide Lockdown

“…This time is coincident with the peak second wave of COVID-19 in India when states had imposed restrictions on the movement of vehicles. Mahato et al ( 2020 ) and Mallik et al ( 2021 ) observed a similar lockdown-period improvement in air quality over Delhi, otherwise one of the most polluted cities in India. Rajesh and Ramachandran ( 2022 ) found a 35% reduction in equivalent black carbon over Ahmedabad, which in turn reduced the aerosol radiative forcing over this location.…”

“…Several studies have reported the decline in atmospheric pollutants over India during the national lockdown. Mallik et al ( 2021 ) reported a significant decrease in the levels of several air pollutants in Delhi. Jain et al ( 2021 ) reported a decline in trace gases and particulate matter over Gadanki, a tropical rural setting in southern India.…”

Exacerbation of Fatality Rates Induced by Poor Air Quality Due to Open-Air Mass Funeral Pyre Cremation during the Second Wave of COVID-19

“…After analyzing the air quality index (AQI) and its various components (O 3 , CO, NO 2 , PM 10 and PM 2.5 ) over Delhi during the second wave of COVID-19, we arrived at a meaningful inference on the pivotal role of air pollutants in worsening the critical condition due to COVID-19. A recent study [18] also reported an enhanced surface ozone level during the lockdown period in 2020 over Delhi. Figure 2 shows the variation in the AQI with the mortality rate during the peak phase of the second wave.…”

Shifts in coral reef fish populations linked to human pressure and tourism activities revealed by COVID-19 restrictions

“…Pandemic-related travel and activity restrictions led to a global 'anthropause' (Rutz et al 2020b) which, in many areas, translated into a decrease in human pressures on ecosystems and in the exploitation of natural resources. From 2020, studies began to highlight reductions in human activities and improvements in water quality in coastal zones throughout the world (review from Mallik et al 2021). Among those, lower noise pollution was observed along a ferry lane in Scandinavia (De Clippele and Risch 2021), and higher fish abundances were linked to decreased fishing activities in the Gulf of Mannar, India (Patterson Edward et al 2021).…”