Festive fireworks in Delhi: A major source of elemental aerosols established through dispersion normalized PMF in a multiyear study

Fireworks activity is behind the substantial increase in particulate concentration during Diwali in Delhi and the concomitantly enhanced atmospheric metal concentration. Therefore, a comprehensive understanding of the impact of fireworks on the atmosphere is crucial to develop a mitigation strategy. Accordingly, this study focuses on the comparative analysis of fireworks events in Diwali across 2019, 2020, and 2021. The current analysis studies the impact of Diwali fireworks for three consecutive years on Delhi's composition, concentration, and ambient PM2.5 sources. The measurement of elements in PM2.5 is performed using an automated ambient metal monitor with sufficient resolution to capture the time variation during the fireworks event. The 12-h average concentrations of elements during Diwali night for 2019, 2020, and 2021 are 181 mu g/m3, 117 mu g/m3, and 151 mu g/m3, respectively. During the fireworks, elemental concentrations like K, Al, Sr, Ba, and S showed distinct peaks and were subsequently identified as tracers. Source apportionment was conducted by applying positive matrix factorization (PMF) to the elemental mass measurements. Dispersion normalized PMF (DN-PMF) was also performed using the time-dependent ventilation coefficient to factor out the impact of meteorology across the three years. The average ventilation coefficient was 3672, 2874, and 2000 m2/s in 2019, 2020, and 2021, respectively. Nine different sources were identified for all three years. The study apportioned over 85% of elemental mass to the firecrackers during Diwali. The average concentrations of the resolved fireworks factor during Diwali night were 154 mu g/m3,107 mu g/m3, and 137 mu g/m3 successively for the three years using the regular PMF, while it was 141 mu g/m3,92 mu g/m3 and 134 mu g/m3 using the DN-PMF. The period of Diwali also overlaps with biomass -burning activities. From the source apportionment results, the period of biomass burning lies in the following Diwali phase (FD) in 2019 and 2021, while it coincides with the Diwali phase in 2020.