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

The mass concentrations of PM 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. The observed annual mean mass concentration of 28 ± 11 µg m is also within the INAAQS value of 40 µg m. The diurnal trend of PM 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 with the highest value during winter (50 ± 22 µg m) and the lowest of (11 ± 5 µg m) in the monsoon. The weekend PM mass concentrations were less than those on the weekdays up to a maximum of 100%. The decrease in PM 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 in this region. The health risk assessment in this study, points to ischemic heart disease as the primary cause of PM-induced death.