Persistence of Primary and Secondary Pollutants in Delhi: Concentrations and Composition from 2017 through the COVID Pandemic

We assess impacts of the 2020 COVID-19 lockdown on ambient air quality in Delhi, building over three years real-time measurements black carbon (BC) and nonrefractory submicrometer aerosol (NR-PM1) composition from Delhi Aerosol Supersite public data regulatory monitoring network. performed source apportionment organic (OA) robust statistical analyses to differentiate lockdown-related baseline seasonal interannual variability. The primary pollutants NOx, CO, BC were most reduced, primarily due lower transportation emissions. Local regional emissions such as agricultural burning decreased during lockdown. PM2.5 declined but remained well above WHO guidelines. Despite lockdown, NR-PM1 changed only moderately compared prior years. Differences trends hydrocarbon-like OA suggest that some sources may have increased. notable reductions pollutants, restrictions led rather small perturbations fraction NR-PM1, with secondary continuing dominate. Overall, our results demonstrate impact pollution Delhi’s show large changes within alone are insufficient bring about needed improvements quality.