Sources and Dynamics of Submicron Aerosol during the Autumn Onset of the Air Pollution Season in Delhi, India

Abstract

New Delhi, India is the most polluted megacity in the world and routinely experiences high particulate matter (PM) concentrations. As part of the Delhi Aerosol Supersite Study, we have been measuring PM1 concentration and composition in Delhi continuously since January 2017. This paper focuses on autumn, one of the most polluted seasons in Delhi when PM1 concentrations steadily increase throughout the season and can exceed 1000 μg m–3 during episodic events. Positive matrix factorization on the organic aerosol (OA) spectrum suggests comparable seasonal average contributions from hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and oxidized OA (OOA), with BBOA dominating during episodic events. We demonstrate the influence of regional sources such as agricultural burning during this season through temporal trends of pollutants, PMF factors, meteorology, and nonparametric wind regression analysis. We use inorganic fragment ratios to show the influence of metals during the festival of Diwali. Furthermore, we demonstrate the influence of transitioning meteorology in governing PM1 composition through the season. Overall, our analysis provides novel insights into the factors controlling PM1 during one of the most polluted seasons in Delhi.