Impact of traffic origin particulate matter and its chemical constituents on oxidative potential

Currently high particulate matter (PM) levels are observed in most of the urban cities of India and one of the major sources of emissions are vehicle plying on roads. Exposure to PM and its components have been linked with various disorders and has been associated with the ability to produce free radicals and reactive oxygen species, known as “oxidative potential” of PM and is proposed to be one of the most relevant indicators of PM toxicity. In the present study we examined the oxidative potential of PM collected at roadside (RS) and urban background (BG) site using dithiothreitol (DTT) assay. PM measurements were carried out simultaneously at both the sites in Mumbai on seven consecutive days, covering both morning (7:00-11:00 AM) and afternoon (12:00-4:00 PM) hours in May 2018 using low volume sampler (Mini vol, Airmetrics, USA flow rate of 5 l min-1). The collected samples was analysed for carbonaceous aerosols (OC, EC, and WSOC) and trace elemental components of PM. The average mass concentration at RS and BG during morning rush hours was 80±23 µgm-3 and 43±10 µgm-3 while in the afternoon it was 84±14.8 µgm-3 and 53±13 µgm-3, respectively. The average OC, EC levels at RS were 19.8±8.8 µgm-3, 16.5±5.1 µgm-3 (morning), 21.8±9.4, 19.1±13.5 µgm-3 (afternoon), whereas at BG site it was 16.5±9.9 µgm-3, 2.5±2.1 µgm-3 (morning), 16±13 µgm-3, 3.5±3.4 µgm-3 (afternoon) respectively. The corresponding WSOC levels at RS and BG were 11% and 19% during morning period while during afternoon it was 15% and 27% of OC, respectively. The volume normalised DTT activity (DTTv) was higher at the roadside (1.12±0.54 nmol min-1 m-3) during morning period than at background (0.75±0.6 nmol min-1 m-3). Thus, our first results suggest that exposure to PM from traffic related emissions may pose substantial risk to a large population in urban areas.