Abstract:The concentrations of PAHs in the atmosphere of a typical background site at Tengchong were investigated once a week from October 22nd, 2005 to October 21st, 2006, aimed to monitor the inflow of PAHs originated from Southeast Asian biomass burning during the monsoon season. The total PAHs concentration ranged from 43.1 to 156 ng/m3, with an average value of 87.9 ng/m3. Average concentration of gas phase PAHs was 85.8 ng/m3, while that of particulate phase PAHs was 2.35 ng/m3. The temporal variation of PAHs in gas phase was not significant. On the contrary, concentrations of PAHs in particle phase elevated in spring. Associated with South Asian monsoon, the transboundary transport of PAHs from Southeast Asian biomass burning to Tengchong could result in the high values of PAHs during this period. PAHs in particle phase were dominated by high molecular congeners with high toxicity, so the accumulation of them in remote ecosystem could increase potential ecological risk.