Persistent organic pollutants in mountain air of the southeastern Tibetan Plateau: seasonal variations and implications for regional cycling.

In order to provide more conclusive evidence of monsoon-driven transport of persistent organic pollutants (POPs) to the Tibetan Plateau (TP) and assess the potential influence of forests on the fate of these pollutants, passive air samplers were consecutively deployed during 2008-2011 on Sygera Mountain (3800 m-4400 m). Higher DDTs levels were observed in the monsoon season (20.5-57.4 pg m(-3)) than the non-monsoon season (9.2-27.4 pg m(-3)), which confirmed that the Indian monsoon plays a key role in driving the atmospheric transport of DDTs to the TP. The similar DDT isomer ratios to the South Asia further suggested that Sygera Mountain is likely a receptor region of Indian subcontinent. By comparing the difference in concentrations between forest and clearing sites, it was found that the forest canopy can reduce airborne DDTs by a factor of 2, indicating strong absorption of DDTs by the Tibetan forest.