Abstract. Current knowledge on atmospheric particle-phase polycyclic aromatic hydrocarbons (PAHs) size distribution remains incomplete. Information is missing on sorption mechanisms and the influence of the PAHs' sources on their transport in human respiratory system. Here we present the studies systematically investigating the modal distribution characteristics of the size-fractioned PAHs and calculating the source contribution to adverse health effects through inhalation. Aerosol samples with nine size fractions were collected from Shanghai urban air over one year period 2012–2013. A high correlation coefficient existed between measured and predicted values (R2= 0.87), indicated that the data worked very well in current study. Most PAHs were observed on the small particles followed with seasonality differences. When normalized by PAHs across particle diameters, the size distribution of PAHs exhibited bimodal patterns, with a peak (0.4–2.1 μm) in fine mode and another peak (3.3–9.0 μm) in coarse mode, respectively. Along with the increasing ring number of PAHs, the intensity of the fine mode peak increased, while coarse mode peak decreased. Plotting of log(PAH/PM) against log(Dp) showed that all slope values were above −1 with the increase towards less-ring PAHs, suggesting that multiple mechanisms, i.e. adsorption and absorption controlled the PAHs on particles, but adsorption played a much stronger role for 5- and 6-ring than 3- and 4-ring PAHs. The mode distribution behavior of PAHs showed that fine particles were major carriers for the more-ring PAHs. Further calculations using inhaling PAHs data showed the total deposition fluxes in respiratory tract were 8.8 ± 2.0 ng h-1. Specifically, fine particles contributed 10–40 % of PAHs deposition fluxes to the alveolar region, while coarse particles contributed 80–95 % of ones to the head region. Estimated lifetime cancer risk (LCR) for people exercised in haze days (1.5 × 10-6) was bigger than the cancer risk guideline value (10-6). The largest PAHs contribution for LCR mainly came from the accumulation particles. Based on source apportionment results generated by positive matrix factorization (PMF), it was found that the cancer risk caused in accumulated mode mainly resulted from biomass burning (24 %), coal combustion (25 %) and vehicular emission (27 %). The present results contribute to a mechanistic understanding of PAHs size distribution causing adverse health effects and will help develop some source control strategies or policies by relying on respiratory assessment data.
Size distributions of polycyclic aromatic hydrocarbons in urban atmosphere: sorption mechanism and source contributions to respiratory deposition
