Size-specific PAHs and Associated Health Risks over a Tropical Urban Metropolis: Role of Long-range Transport and Meteorology

The polycyclic aromatic hydrocarbons (PAHs) are considered as an important class of organic pollutants in the urban atmosphere to pose serious health hazards A comprehensive study was conducted during the dry seasons of 2017-2018 to understand the impacts of local sources, meteorology, boundary layer dynamics, and long-range transport, on the size-specific particulate PAHs (Coarse: 10-2.1 mu m; Superfine: 2.1-1.1 mu m; Accumulation: 1.1-0.4 mu m and Ultrafine: < 0.4 mu m). Samples were collected over Kolkata (22.33 degrees N and 88.20 degrees E), a megacity of the lower Indo-Gangetic Plain (IGP). Wintertime distributions of all PAHs were exclusively unimodal with their maximum abundance in accumulation mode, whereas the 4,5 and 6-ring PAHs showed additional coarse mode peaks during post-monsoon and pre-monsoon. The Concentration Weighted Trajectory model has identified the middle IGP and the Eastern Ghats as the potent PAH source regions for the receptor site. Meteorology significantly influenced, in minimizing the contributions of transported PAHs from biomass burning regions of Eastern Ghats during pre-monsoon. On the contrary, meteorology favored the PAHs accumulation from local emissions and long-range transport during winter and post-monsoon. Source apportionment by positive matrix factorization model identified unburned petroleum, incineration, fossil fuel and coal burning as possible major sources of size-specific PAHs. Additionally, based on benzo(a)pyrene equivalent concentrations, the incremental lifetime cancer risk (ILCR) values were estimated for four human age groups. In general, ILCR values were influenced by the accumulation mode, and they were highest for all size ranges during winter. The estimated upper limit of ILCR (9.26 x 10(-6)) exceeding the carcinogenic benchmark level (1 x 10(-6)), draws attention towards the adverse impacts of wintertime ultrafine PAHs on human health in Kolkata, where poor air quality is already a major concern.