Investigating PM2.5 Oxidative Potential and Its Association with Chemical Constituents Measured outside of Urban Residences in Three Metropolitan Cities of India.

BACKGROUND: Redox-active potent species present in fine particulate matter [PM  ≤ 2.5 μm in aerodynamic diameter ( PM2.5 )] have been suggested as one of the major sources of oxidative stress- and health-related disorders in the urban population. OBJECTIVES: Our objective was to determine PM2.5 oxidative potential (OP) in urban residential neighborhoods having different sources of PM2.5 (traffic emissions, commercial, and residential activities) in three metropolitan Indian cities. METHODS: We investigated the neighborhood and seasonal variation in PM2.5 OP across three metropolitan cities (Delhi, Mumbai, and Bengaluru) in India. Low-cost samplers were used to collect PM2.5 outside balconies, ground floors, and first floors of residential buildings for 24 h. We used acellular assays, including dithiothreitol (DTT) and ascorbic acid (AA), to examine the particle toxicity. Bivariate and multiple linear regression analyses were conducted to examine the association of OP with the analyzed PM constituents. RESULTS: The extrinsic OPDTTv levels, were comparable between the cities, with the highest levels observed in Delhi ( mean ± standard deviation : 3.82 ± 1.56 nmol/min/m3 ), exceeding those in Mumbai and Bengaluru by a factor of 1.03 and 1.21, respectively. For intrinsic OP, ( OPDTTm ), Bengaluru exhibited the maximum toxicity, followed by Mumbai and Delhi. Bengaluru demonstrated significant OP variation compared with both Delhi and Mumbai. OPAA showed comparable trends in both intrinsic and extrinsic variation. Further, on comparing intra-urban variability, OPDTTv was highest in all cities in the high-traffic neighborhoods, ranging from 5.13 to 4.22 nmol/min/m3 . Bengaluru residential neighborhoods were  ∼ 4 and 6 times higher in OPAAm compared with Delhi and Mumbai residential neighborhoods, respectively. Among residential neighborhoods, the coefficient of divergence (COD) showed  ∼ 1.5 times higher heterogeneity in OPAAv than OPDTTv . Carbonaceous fractions and a few transition elements were strongly correlated ( p < 0.05 ) with OP assays. In Mumbai, comparable OPDTTv levels were observed in both seasons, winter and summer, suggesting that toxicity is more likely influenced by the primary-originated traffic aerosols. Water-soluble organic carbon, cobalt (Co), and vanadium (V) were the primary contributors to reactive oxygen species activity. DISCUSSION: Our study reveals that PM toxicity outside of residential homes in traffic-dominated neighborhoods is significant compared with other neighborhoods across all metropolitan cities. This emphasizes the potential health risks associated with PM originating from traffic sources. https://doi.org/10.1289/JHP1007.