Temporal variability of PM_2.5 and its possible sources at the tropical megacity, Bengaluru, India

The mass concentrations of PM_2.5 were measured at a tropical megacity, Bengaluru, India, for the year 2015. The mean mass concentrations showed large fluctuations on day to day basis with values less than the Indian National Ambient Air Quality Standard (INAAQS) of 60 µg m^-3. The observed annual mean mass concentration of 28 ± 11 µg m^-3 is also within the INAAQS value of 40 µg m^-3. The diurnal trend of PM_2.5 concentration showed bimodal distribution, with the primary peak in the morning and the secondary one during the late evening hours. The timing of the peaks matched with rush traffic hours. Strong seasonality is observed in the diurnal concentration of PM_2.5 with the highest value during winter (50 ± 22 µg m^-3) and the lowest of (11 ± 5 µg m^-3) in the monsoon. The weekend PM_2.5 mass concentrations were less than those on the weekdays up to a maximum of 100%. The decrease in PM_2.5 mass concentration was also observed on the day of the strike when many busses were off the road. Vehicular traffic is suggested as one of the primary contributors of PM_2.5 in this region. The health risk assessment in this study, points to ischemic heart disease as the primary cause of PM_2.5-induced death.