Characteristics and sources of non-methane hydrocarbons in background atmospheres of eastern, southwestern, and southern China

Abstract

Non-methane hydrocarbons (NMHCs) play very important roles in atmospheric chemistry, yet little is known about their abundance in the atmosphere of China, especially in the background atmospheres. Measurements of C₂-C₁₀ NMHCs were concurrently carried out at two remote background sites and one rural background site in April and May 2004 in this study: Tengchong Mountain (TM) in Yunnan province on the border of southwestern China; Jianfeng Mountain (JM) on the southwest coast of Hainan Island, southern China; and Lin'an (LA) in Zhejiang province in eastern China. Additional samples were collected at an urban site, Tengyue Town (TT, about 10 km from TM), to obtain local urban NMHC profiles. NMHC levels in these background sites were compared with other rural and remote sites in Asia and other global background stations. In the urban site of TT, local biofuel combustion was the major contributor to the high levels of ethene, ethyne, and ethane. In LA, the major sources of NMHCs were the emissions from fossil fuel and biofuel combustion and from industrial solvent use. Compared with another study conducted in 2001, toluene levels had increased by 75% in 2004 in this study, whereas the levels of other anthropogenic hydrocarbons remained at the same levels. Local industrial emissions and transports from the Yangtze River Delta were the major sources of toluene, ethylbenzene, and xylenes in LA. While in TM, the major sources were regional biofuel combustions and biomass burning emissions from Southeast Asia. Long-range transport of air masses from Southeast Asia was the major source of NMHCs in JM in spring. JM showed the lowest levels of most hydrocarbons among the three background sites. Several hydrocarbon molar ratios, such as benzene/toluene and ethane/propane, were used to characterize the signatures of air masses from different regions.