COVID-19 Lock-down in Delhi: Understanding Trends of Particulate Matter in Context of Land-Use Patterns, GIS Mapping, and Meteorological Traits

The effectiveness and cost implications are always top factors for policy makers while deciding upon the appropriate air pollution abatement measures. The present study aimed to understand the actual particulate matter (PM2.5 and PM10) patterns during different phases of COVID-19 lockdown periods and depict their spatial distributions covering the 36 major areas in Delhi, India. Drastic visible reduction in both the pollutants was found during lockdown phase 1 and 2. Average PM2.5 reductions of 41.97%, 39.24%, 56.04%, and 56.77% were recorded comparing lockdown and/or study period with the years 2018, 2019, 2021, and 2022, respectively. Similar average reduction of PM10 to the magnitude of 51.72%, 48.95%, 48.24%, and 49.00% was found for the referred years. However, the reduction during the before-lockdown period of 2018 and 2019 and the year 2020 did not follow such radical reduction returning the values for PM2.5 as 7.66-14.88% and that for PM10 as 12.86-20.67%. The geospatial maps generated for Delhi city followed the similar findings at macro level depicting huge reduction in PM distribution classes for the study period. For instance, the percent surface area under "moderately high"polluted due to PM2.5 came down to 0.61 during lockdown phase 2 from 13.96 during January 2020. Further, about 15 of the 36 locations reported compliance to the National Ambient Air Quality Standards (NAAQS) for either of the pollutants during the study period. Nevertheless, such reductions are short-lived because the levels went up again in the years 2021 and 2022 (except similar lockdowns) as the situation got back to normal daily life activities postlockdown. Although, lockdown may be imposed in case of severe ambient air quality in a densely populated megacity like Delhi, it remains a temporary or quick-fix solution, to be looked as a last line of defense. © 2023 Mary Ann Liebert, Inc., publishers.

Phase-Resolved Lockdown Features of Pollution Parameters Over an Urban and Adjoining Rural Region During COVID-19

In this study, we investigate the temporal variations in columnar aerosol pollutants and their possible association with the simultaneously measured black carbon (BC) aerosol mass concentration and associated biomass burning (BB) over urban (Delhi) and rural (Panchgaon) sites during the lockdown phases of the COVID-19 pandemic. We also show the impact of lockdown measures on boundary layer ozone and its primary precursors, NO2, and water vapor (H2O), potent greenhouse gases that destroy protective ozone. For this purpose, we used multiple datasets, namely, black carbon (BC) aerosol mass concentration and biomass burning (BB) aerosols using an aethalometer at Amity University Haryana (AUH), Panchgaon, India, and satellite retrievals from NASA’s MODIS and OMI at both the stations. The analysis was conducted during the pre-lockdown period (1–25 March), lockdown 1st phase (25 March–14 April), lockdown 2nd phase (15 April–3 May), lockdown 3rd phase (4–17 May), lockdown 4th phase (18–31 May), and post-lockdown (1–30 June) period in 2020. Our diagnostic analysis shows a substantial reduction in AOD (Delhi: −20% to −80%, Panchgaon: −20% to −80%) and NO2 (Delhi: −10% to −42.03%, Panchgaon −10% to −46.54%) in comparison with climatology (2010–2019) during all four phases of lockdown. The reduction in AOD is attributed to lockdown measures and less transport of dust from west Asia than climatology. Despite a reduction in NO2, there is an increase in the ozone amount (Delhi: 1% to 8% and Panchgaon: 1% to 10%) during lockdown I, II, and III phases. The observed enhancement in ozone may be resultant from the complex photochemical processes that involve the presence of NO2, CO, volatile organic compounds (VOCs), and water vapor. The reduction in AOD and NO2 and enhancement in ozone are stronger at the rural site, Panchgaon than that at the urban site, Delhi. Copyright © 2022 Sonbawne, Fadnavis, Vijayakumar, Devara and Chavan.

Multisite characterization of concurrent black carbon and biomass burning around COVID-19 lockdown period

The Magee Scientific Model AE33 Next Generation Aethalometer, installed at Amity University Haryana (AUH), Panchgaon (rural station) has been operated round-the-clock and obtained high-resolution (1–5 Minutes) observations of Black Carbon (BC) mass concentration at seven different sensing wavelengths (ranging from UV to NIR). For each observation, contribution from Biomass Burning (BB, in percent) to the BC has also been recorded. These measurements have been analyzed to segregate different sources, responsible for BC at this rural station. The results reveal that the major contributor is ‘traffic’ (fossil-fuel diesel emissions), followed by ‘biomass smoke’, wood-burning activities. The diurnal variation in BC and associated BB over this study area reveals a significant maximum around 0900 h and minimum around 1600 h. These maximum and minimum concentrations are attributed to transport activities during morning and ascending of local atmospheric boundary-layer height. The results also exhibit a strong affinity between BC mass concentration and coincident CO2 and PM2.5 mass concentrations. Synchronous BC measurements have also been organized over two more locations, namely, Bhopal (urban station) and Mahabaleshwar (high-altitude station). The black carbon aerosol transport through long-range air mass back-trajectories is explained. © 2021