Ambient distribution of particulate- and gas-phase n-alkanes and polycyclic aromatic hydrocarbons in the Tibetan Plateau

Attention has been paid for the levels, sources and health risks of atmospheric aliphatic and polycyclic aromatic hydrocarbons (n-alkanes and PAHs) in remote areas, however, few studies have focused on those in the Tibetan Plateau. In this study, 18 pairs of atmospheric samples were obtained during the period from August 2006 to July 2007 in Lhasa, the capital city of Tibet. Both gas-phase and particulate-phase n-alkanes and PAHs were measured. Concentrations of n-alkanes (gas + particulate phase, 99.1-480.9 ng/m(3)) and PAHs (gas + particulate phase, 11.4-72.5 ng/m(3)) in Lhasa are lower than those in many cities. The sources of n-alkanes related to biological and petroleum sources were 67 and 33%, respectively. According to the results of diagnostic ratios and principal component analysis, emission of traffic vehicles was one of the important PAH sources, and sources of benzo(a)pyrene was likely attributed to incense burning. Good simulations were obtained by traffic soot-based model for fluoranthene, pyrene and benzo(a)anthracene, while, wood soot-based model fitted the experimental results of benzo(a)pyrene better. This meant atmospheric fate of PAHs was mainly influenced by the adsorptive partitioning that occurred during traffic and incense burning procedures. In addition, the benzo[a]pyrene-equivalent carcinogenic power (BaPE) in the present study (0.1-1.6 ng/m(3)) is lower than those in other cities and also the air quality standard of China, suggesting that atmospheric PAHs caused low health risks.