Mixing ratios and sources of halocarbons in urban, semi-urban and rural sites of the Pearl River Delta, South China

Abstract

The pearl river delta (PRD) region is one of the most important industrial and manufacturing centers of China and the world. In order to explore the regional mixing ratios of halocarbons in the PRD atmosphere and to reconcile the major halocarbon emission sources, air samples were collected in an urban site in Guangzhou City, a semi-urban site in Panyu and a rural site on Dinghu Mountain, as well as roadside sites and vehicular tunnels of the PRD in 2001 and 2004. The samples were analyzed for a variety of carbon-containing compounds. The results revealed elevated regional mixing ratios of most halocarbons, especially trichloroethene (C 2HCl 3), methyl iodide (CH 3I), tetrachloroethene (C 2Cl 4), bromochlorodifluoromethane (Halon-1211, CBrClF 2), 1-dichloro-1,1-fluoroethane (HCFC-142b, CH 3CClF 2) and trichloromethane (CHCl 3) when compared with the background levels of the western Pacific and East Asian coast, and the Northern Hemisphere suggesting that there are significant sources of halocarbons in the PRD region. Higher dichlorodifluoromethane (CFC-12, CCl 2F 2), 1,1,1-trichlorotrifluoroethane (CFC-113, CCl 2FCClF 2), dibromomethane (CH 2Br 2) and tribromomethane (CHBr 3) mixing ratios were found in the tunnels and roadside samples when compared with the ambient samples. In these samples, CH 2Br 2 and CHBr 3 correlated well with each other and methyl bromide (CH 3Br) suggesting they are associated with exhaust emissions from vehicles running on leaded gasoline. High levels of methyl halides: methyl chloride (CH 3Cl), CH 3Br and CH 3I, and CH 2Br 2, bromodichloromethane (CHBrCl 2), CHBr 3 and dimethyl sulfide (C 2H 6S, DMS) were simultaneously observed in the oceanic air masses that originated from the coastal areas of southeast China and had passed over the Pearl River Estuary. Good correlations were found between CH 2Br 2 and CHBr 3 with linear regression slopes of 0.17 and 0.15 for the Dinghu Mountain and Guangzhou City samples, respectively, and between CH 3I and CHBr 3, and DMS suggesting that emissions from the coastal territorial ecosystems of the PRD are important sources of the methyl halides, CH 2Br 2, CHBrCl 2, CHBr 3 and DMS observed.