Effect of Biomass Burning, Diwali Fireworks, and Polluted Fog Events on the Oxidative Potential of Fine Ambient Particulate Matter in Delhi, India

Abstract

We investigated the influence of biomass burning (BURN), Diwali fireworks, and fog events on the ambient fine particulate matter (PM_2.5) oxidative potential (OP) during the postmonsoon (PMON) and winter season in Delhi, India. The real-time hourly averaged OP (based on a dithiothreitol assay) and PM_2.5 chemical composition were measured intermittently from October 2019 to January 2020. The peak extrinsic OP (OP_v: normalized by the volume of air) was observed during the winter fog (WFOG) (5.23 ± 4.6 nmol·min^-1·m^-3), whereas the intrinsic OP (OP_m; normalized by the PM_2.5 mass) was the highest during the Diwali firework-influenced period (29.4 ± 18.48 pmol·min^-1·μg^-1). Source apportionment analysis using positive matrix factorization revealed that traffic + resuspended dust-related emissions (39%) and secondary sulfate + oxidized organic aerosols (38%) were driving the OP_v during the PMON period, whereas BURN aerosols dominated (37%) the OP_v during the WFOG period. Firework-related emissions became a significant contributor (∼32%) to the OP_v during the Diwali period (4 day period from October 26 to 29), and its contribution peaked (72%) on the night of Diwali. Discerning the influence of seasonal and episodic sources on health-relevant properties of PM_2.5, such as OP, could help better understand the causal relationships between PM_2.5 and health effects in India.