Sources of polycyclic aromatic hydrocarbons in PM2.5 over the East China Sea, a downwind domain of East Asian continental outflow

Abstract

A receptor site in the East China Sea (ECS), ∼66 km off the shore of Shanghai, was used to investigate the seasonally atmospheric transport of land-based PAHs. Positive matrix factorization (PMF) modeling and back trajectories were performed to apportion the sources of the 16 USEPA priority PAHs (16 PAHs). In the process, three episodes were observed in all seasons except summer. These episodes provided additional insight to the transport mechanisms of these air pollutants in this most developed region of China. The average concentrations (in ng/m3) of PAHs in PM2.5 in fall, winter, spring and summer were 5.26 ± 5.36, 10.41 ± 8.58, 3.93 ± 2.31 and 0.97 ± 0.25, respectively, and with an annual average of 5.24 ± 5.81. Low molecular weight (LMW) PAHs (i.e., 2 ∼ 3-ring) was a dominant contributor for the 16 PAHs in PM2.5 over the ECS (36.2%), especially in summer (55.6%). The source apportionment by PMF analysis indicated that, based on yearly average, vehicular emission (27.0%) and coal combustion (24.5%) were the two major sources of PAHs, followed by biomass burning (16.5%), petroleum residue (16.3%) and air–surface exchange (15.7%). The highest source contributor for PAHs in fall and winter was coal combustion (30.5%) and vehicular emission (34.5%), respectively; while in spring and summer, the air–surface exchange contributed the most (27.1% and 59.5%, respectively). The specific composition patterns of 16 PAHs and PMF modeling results manifested that the air–sea exchange could be a potential source for the LMW PAHs in PM2.5 over the ECS, especially in warm season.