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Influence of the COVID-19 Lockdown on Delhi's Air Quality
KANAN PATEL, Mark Campmier, Sahil Bhandari, Nisar Ali Baig, Gazala Habib, Joshua Apte, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 487
Working Group: Urban Aerosols
Abstract
To reduce the spread of COVID-19, a nationwide lockdown was implemented in India from Mar 24-May 31, 2020. Here, we assess the impacts of this lockdown on ambient air quality in Delhi, building on nearly four years of ongoing measurements of non-refractory submicron aerosol (NR-PM1) composition using an aerosol chemical speciation monitor and black carbon (BC) via an aethalometer from the Delhi Aerosol Supersite (DAS). We obtained additional pollutant data (PM2.5, CO, NOx, O3, SO2) from the regulatory monitoring sites across the city.
Average NR-PM1 dropped sharply (~40%) at the outset of the lockdown, assessed based on comparing multi-week periods before and after Mar-24. While the lockdown likely had a role to play, meteorology was also an important factor considering the influence of unseasonable precipitation around the initial period of the lockdown, as well as the usual seasonal increase in ventilation and temperature in the spring/summer period. Considering the full lockdown period, the bulk NR-PM1 concentration was strikingly similar to the previous three years, with only modest changes in the lockdown period compared to prior years. The largest difference relative to prior years was a ~two-fold reduction in particulate sulfate. Relative to prior years, we also observed large reductions in BC, CO, and NOx, and increases in O3, likely because of sharp reductions in traffic emissions.
Positive matrix factorization (PMF) of the organic aerosol (OA) mass spectra resolved three factors–HOA (hydrocarbon-like-OA), OBBOA (oxidized-biomass burning-OA) and OOA (oxidized-OA). Comparing the lockdown period against pre-lockdown conditions, average HOA and OOA concentrations decreased by ~33-35% while average OBBOA remained practically unchanged, likely due to influence of regional agricultural burning in May.
Overall, our results provide valuable evidence on atmospheric aerosol dynamics in Delhi, and by inference, how future large-scale modification of activity and/or emissions might contribute to improvements in Delhi’s air quality.