Interplay between oxidative potential and health risk of PM _2.5 -bound metals at a site of the Indo-Gangetic Plain—exploring the influence of biomass burning

Biomass burning (BB) contributes to deteriorating air quality, particularly elevated haze periods during winter. This study investigates the impact of BB aerosols on PM_2.5 composition and toxicity at a suburban site in Agra, India, during both haze and non-haze periods. Satellite and model retrievals alongside meteorological parameters were studied to estimate air mass trajectories and total fire events to assess the contribution of long-range transported BB aerosols. The samples were collected and analyzed for metal composition using ICP-OES and oxidative potential using dithiothreitol (DTT) assay. The total PM_2.5 mass was significantly found higher in haze periods (236.6 ± 19.9 μg m^-3) compared to non-haze periods (137.1 ± 45.7 μg m^-3). Potassium (K), a signature marker of BB, dominated the metal composition along with carcinogenic metals Cd, Cr, Ni, and Pb and was also prominent during haze periods. The DTT assay showed higher ability to generate oxidative stress during haze periods, strongly correlating with metals, Cr (<i>r</i> = 0.81), Cu (<i>r</i> = 0.65), Mn (<i>r</i> = 0.67), Fe (<i>r</i> = 0.66), and Zn (<i>r</i> = 0.50), along with BB-related metals, K (<i>r</i> = 0.90), Na (<i>r</i> = 0.91), and Mg (<i>r</i> = 0.81), indicating their role in ROS generation. The health risk was estimated through health risk assessment (HRA) that aligns with OP measurements, indicating inhalation as the primary exposure pathway and adults as the higher risk group (HI = 2.9, CR = 4.3 × 10^-4) due to elevated exposures mainly to Cr, Cd, Mn, Ni, and Pb. This suggests increased non-carcinogenic and carcinogenic risks due to the contribution of BB-derived metals to oxidative stress. Positive matrix factorization identified agricultural dust and BB (46.9%) as the major contributors to PM_2.5. Thus, based on these findings, implementing effective mitigation policies to control BB emissions, particularly during winter which contributes to haze periods, is crucial.