Particulate Oxidative Potential Associated with Fireworks Activity during Diwali at a site in the Indo-Gangetic Plain

Abstract

The dithiothreitol (DTT) assay was used to investigate the oxidative potential (OP) of atmospheric fine particles (PM2.5) to form reactive oxygen species (ROS) during Diwali festival firework activity at a site in the Indo-Gangetic Plain, India. During the study period, the 12-hour mean PM2.5 was reported to be 263 ±151 µg m-3, which was 4.4 times higher than the NAAQS standards. Increased levels of gaseous pollutants (NOx, SO2, CO and O3), as well as metal concentrations such as Ba, Pb, Cu, Fe, Mg, K, Al, and Mn, were also observed during fireworks displays. The increased PM2.5-NOx slope for fireworks, which included traffic emissions, revealed that fireworks played a significant role. The highest value of OP of PM was detected in the next morning of Diwali, with a volume-based DTT value of 1.4 nmol min-1 m-3 and a mass-based DTT value of 11.8 pmol min-1 μg-1, implying higher PM-related DTT activity due to fireworks. A positive association was found between redox-active metals like Cr, Cu, Ni, and V and DTT activity which could be due to the ability of these metals to catalyse ROS generation in ambient air. Ba and Se concentrations in the particulate matter, which are key components of firecrackers, were likewise highly linked to DTT activity. During the daytime, ozone levels were strongly correlated (r2 = 0.9) with OPv activity; this may be due to photochemical processes which may lead to the formation of tropospheric O3. Elements C, O, Al, Si, S, K, and Ba were found to be the most prevalent in elemental mappings, which suggests that fireworks may have contributed to their abundance. A comparison of the daily OPv activity and hazard index (HI) suggests that the HI may be a poor metric for measuring the health impacts of PM exposure on human health.