Nonmethane hydrocarbons in the transported and local air masses at a clean remote site on Hainan Island, south China

Nonmethane hydrocarbons (NMHCs) were investigated in a clean remote tropical rain forest site of Jianfengling Natural Reserve in Hainan Island in spring, autumn and early winter of 2004. The aim was to characterize air pollution transported from east Asia and SE Asian subcontinent on this relatively undeveloped region of south China. Ethane, ethyne, isoprene and ethene are the most abundant hydrocarbons. The relative contributions of pollution transport from urban and industrial zones of east Asia and agricultural zones of SE Asia are discussed with the help of backward air trajectories. The air masses from the SE Asian biomass burning region contained higher concentrations of ethane and ethyne while air masses traveling through coastal east China contained higher concentrations of ethene and toluene in addition to ethane and ethyne. It was found that anthropogenic emissions transported from the SE and south China developed and developing regions in autumn had a higher input than biomass burning emission from SE Asia in spring. Local biogenic emission was deduced to be the major source of isoprene. Hydrocarbon concentration ratios were found to be good indicators for identification of inflow air masses from different source regions.