Nationwide increase of polycyclic aromatic hydrocarbons in ultrafine particles during winter over China revealed by size-segregated measurements

Polycyclic aromatic hydrocarbons (PAHs) are toxic compounds in the atmosphere and have adverse effects on public health, especially through the inhalation of particulate matter (PM). At present, there is limited understanding of the size distribution of particulate-bound PAHs and their health risks on a continental scale. In this study, we carried out a PM campaign from October 2012 to September 2013 at 12 sampling sites simultaneously, including urban, suburban and remote sites in different regions of China. Size-segregated PAHs and typical tracers of coal combustion (picene), biomass burning (levoglucosan) and vehicle exhaust (hopanes) were measured. The annual averages of the 24 total measured PAHs (Sigma(24)PAHs) and benzo[a]pyrene (BaP) carcinogenic equivalent concentration (BaPeq) ranged from 7.56 to 205 ng/m(3) with a mean of 53.5 ng/m(3) and from 0.21 to 22.2 ng/m(3) with a mean of 5.02 ng/m(3), respectively. At all the sites, Sigma(24)PAHs and BaPeq were dominant in the ultrafine particles with aerodynamic diameter < 1.1 mu m, followed by those in the size ranges of 1.1-3.3 mu m and > 3.3 mu m. Compared with southern China, northern China witnessed much higher Sigma(24)PAHs (87.36 vs. 17.56 ng/m(3)), BaPeq (8.48 vs. 1.34 ng/m(3)) and PAHs' inhalation cancer risk (7.4 x 10(-4) vs. 1.2 x 10(-4)). Nationwide increases in both PAH levels and inhalation cancer risk occurred in winter. The unfavorable meteorological conditions and enhanced emissions of coal combustion and biomass burning together led to severe PAHs' pollution and high cancer risk in the atmosphere of northern China, especially during winter. Coal combustion is the major source of BaP eq in all size particles at most sampling sites. Our results suggested that the reduction of coal and biofuel consumption in the residential sector could be crucial and effective in lowering PAH concentrations and their inhalation cancer risk in China.