Seasonal variation and health risk assessment of atmospheric polycyclic aromatic hydrocarbons (PAHs) in the urban area of Xi'an

Gaseous samples and total suspended particles (TSP) in the atmosphere of Xi'an city were collected from August 2008 to July 2009. The sixteen U. S. EPA priority PAHs were characterized to investigate their seasonal variation in concentration and composition. Human health risk caused by the PAHs was also assessed. The results showed that total concentration of the sixteen PAHs (∑PAHs) in the urban air ranged from 37 to 620 ng·m ^-3 with an average of 195 ng·m ^-3 during the sampling period. The highest concentration of PAHs was found in winter (360 ng·m ^-3 in average), followed by autumn (213 ng·m ^-3), spring (106 ng·m ^-3) and summer (74 ng·m ^-3). Molecular compositions indicated that the gaseous PAHs were mainly composed of 3~4 rings congeners, while the particulate PAHs were largely composed of 5~6 rings. Diagnostic ratios of the PAHs revealed that coal burning, motor vehicle exhaust and biomas burning emission were the major sources in the city. Health risk assessment of PAHs for adults and children in Xi'an was conducted by means of the health risk assessment model and benzo(a)pyrene (BaP)-toxic equivalent factor. The results showed that average daily exposure dose was 24.3×10 ^-6 mg·kg ^-1·d ^-1 and 5.6×10 ^-6 mg·kg ^-1·d ^-1 for adults and children, respectively. The excess risks for lifelong carcinogenic disease of adults and children were separately 7.5×10 ^-5 and 1.7×10 ^-5, possibly exceeding the acceptable levels. The expected loss of lifetime caused by the PAHs would be 467.6 and 107.5 min for adults and children, respectively.