Phase distribution, sources and risk assessment of PAHs, NPAHs and OPAHs in a rural site of Pearl River Delta region, China

Gaseous and particulate samples were collected in the late autumn of 2010 from Wanqingsha (WQS), a rural site in the Pearl River Delta (PRD) region, China. Eighteen polycyclic aromatic hydrocarbons (PAHs), twenty-nine nitrated PAHs (NPAHs) and six oxygenated PAHs (OPAHs) were measured, and their gas-particle partitioning, sources and risks were discussed. The results showed that the atmospheric mass distribution was dominated by three and four rings compounds. Phenanthrene, 2-nitrofluoranthene and benzanthrone were the most abundant parent PAH, NPAH and OPAH, respectively. The partitioning of these compounds was strongly dependent on their molecular weights. The absorption model provides a better prediction of the particulate fraction of PAHs than the adsorption model, and might be applied for the discrimination of PAH derivatives sources. Molecular diagnostic ratios suggested that coal combustion or biomass burning, not vehicle emission, were the dominant sources in WQS. The ratios of 2-nitrofluoranthene/2nitropyrene and 2-nirtofluoranthene/1-nitropyrene indicated that secondary formation by OH initiated reactions was the main formation pathway for NPAHs, with an average contribution of 92.6% during the sampling period, and the formation might be enhanced under hazy conditions. Most of OPAHs were under the impact of regional pollution. Risk assessment showed an overall lifetime excess inhalation cancer risk of 1.12x10(-5) in which the six NPAHs taken into calculation contributed 3.5% although they only accounted for 0.7% of the 18 compound masses used in the assessment.