中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS Atmospheric Environment 40 (2006) 7331–7345 www.elsevier.com/locate/atmosenv Mixing ratios and sources of halocarbons in urban, semi-urban and rural sites of the Pearl River Delta, South China C.Y. ChanÃ, J.H. Tang, Y.S. Li, L.Y. Chan Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong Received 12 January 2006; received in revised form 29 June 2006; accepted 29 June 2006 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 (C2HCl3), methyl iodide (CH3I), tetrachloroethene (C2Cl4), bromochlor- odifluoromethane (Halon-1211, CBrClF2), 1-dichloro-1,1-fluoroethane (HCFC-142b, CH3CClF2) and trichloromethane (CHCl3) 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 dichlorodifluor- omethane (CFC-12, CCl2F2), 1,1,1-trichlorotrifluoroethane (CFC-113, CCl2FCClF2), dibromomethane (CH2Br2) and tribromomethane (CHBr3) mixing ratios were found in the tunnels and roadside samples when compared with the ambient samples. In these samples, CH2Br2 and CHBr3 correlated well with each other and methyl bromide (CH3Br) suggesting they are associated with exhaust emissions from vehicles running on leaded gasoline. High levels of methyl halides: methyl chloride (CH3Cl), CH3Br and CH3I, and CH2Br2, bromodichloromethane (CHBrCl2), CHBr3 and dimethyl sulfide (C2H6S, 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 CH2Br2 and CHBr3 with linear regression slopes of 0.17 and 0.15 for the Dinghu Mountain and Guangzhou City samples, respectively, and between CH3I and CHBr3, and DMS suggesting that emissions from the coastal territorial ecosystems of the PRD are important sources of the methyl halides, CH2Br2, CHBrCl2, CHBr3 and DMS observed. r 2006 Elsevier Ltd. All rights reserved. Keywords: Halocarbons; Montreal Protocol; Air pollutant emissions; Pearl River Delta and China 1. Introduction The industrialized pearl river delta (PRD) region is one of the most important manufacturing centers of South China. The increasing population, rapid ÃCorresponding author. Tel.: +852 2766 4475; fax: +852 2334 6389. mobilization, urbanization and industrialization in E-mail address: [email protected] (C.Y. Chan). the last two decades have resulted in emissions of 1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.06.041 转载 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7332 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345 huge amount of air pollutants into the atmosphere China is required to reduce 50% of the 1995–1997 and a rapid degradation of air quality in the PRD average baseline of CFC production and consump- region and downwind South China region tion by year 2005 and 100% by 2010 (UNEP, 2003). (HKEPD, 2002; Chan et al., 2004). Severe air An intensive sampling of air samples was conducted pollution caused by photochemical ozone, particu- in urban, semi-urban and rural sites, as well as late matters and toxic air pollutants has been roadside sites and vehicular tunnels of the PRD. reported for various cities of the PRD region (e.g. Such a campaign is to explore the scientific aspects Wang et al., 2002a, b; Wang and Kwok, 2003; Zhao relating to atmospheric halocarbons and to recon- et al., 2004). The export of the PRD air pollution as cile the major halocarbon emission sources, which a part of Asian outflow and its impact on the are the fundamental information for formulation of regional and global atmosphere has attracted much a successful control strategy. The air samples were scientific interest (e.g. Jacob et al., 2003; Parrish et analyzed for a variety of carbon-containing com- al., 2004). However, relatively limited attention has pounds. In this paper, the results of halocarbons are been paid to characterize the atmospheric abun- presented and analyzed. The possible sources of dance and emissions of halocarbons in the PRD selected important halocarbons in the PRD region region. will also be discussed. Halogenated hydrocarbons (halocarbons) con- tain a wide range of compounds of various 2. Sampling and laboratory analysis environmental importance. Halocarbons have been a focus of scientific research for their vital roles in Fig. 1 shows the geographical locations of the stratospheric ozone depletion. Many halocarbons three sampling sites. The rural site is located on are efficient greenhouse gases (WMO, 2002), whilst Dinghu Mountain within the Dinghu Botanical some chlorinated hydrocarbons (e.g. trichloroethy- Garden (23.101N, 112.321E), which is located at lene and chloroform) are toxic to human health around 100 km to the west of Guangzhou City (a (Grosjean et al., 1999). The consumption of population of 8.2 million). The sampling site is halocarbons, especially chlorofluorocarbons situated at around 400 m above the sea level and (CFCs), is now being phased out under the terms around 1.5 m above the ground surface. Panyu (a of the Montreal Protocol and its Amendments. population of 0.94 million) is located on the Hydrochloroflurocarbons (HCFCs) and hydro- southern edge of Guangzhou City at about 20 km fluorocarbons (HFCs) are important interim sub- south of the major metropolitan areas, and about stitutes for CFCs. Under the Montreal Protocol, 40 km north of the industrial city Dongguan Fig. 1. Map showing the sampling sites and the Pearl River Delta region. 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345 7333 (a population of 1.6 million), and 45 km north of canisters through the window to around 0.5 m away Zhongshan city (a population of 2.4 million). This from the vehicle. The roadside samples were also sampling site is located at a suburban area in an collected at around 1.6 m above ground level on the open area relatively away from nearby buildings pavement next to the road traffic. The sampling and at about 3 m above ground surface. The urban duration for each sample was 2–3 min. The air site is located in Guangzhou City at Liwan district. samples were shipped back to UC-Irvine and The sampling site is located about 30 m above analyzed for carbon monoxide (CO), methane ground on top of a 13 story building. On Dinghu (CH4), carbonyl sulfide (OCS), DMS, carbon Mountain and Guangzhou City, field sampling was disulfide (CS2), 24 C1–C2 halocarbons and 45 conducted in the spring of 2001, while in Panyu it C2–C10 non-methane hydrocarbons (NMHCs) with was conducted in autumn and early winter of 2004. a system that comprises five different gas chromato- These seasons are the transition periods of the graphic columns each equipped with electron- winter and summer monsoons, when continental air capture detector, flame-ionization detector, quadro- masses and fine weather usually prevail. There were pole mass spectrometric detector. Carbon monoxide altogether 39 samples collected in Guangzhou City and CH4 were analyzed by separate systems using a from 3 to 19 March 2001, 42 samples on Dinghu portion of a sample. The analytical systems and Mountain from 3 to 26 March 2001 and 15 samples experimental methods are similar to those described in Panyu from 1 to 7 September, 23–29 November by Colman et al. (2001). Both systems were and 1–4 December 2004. In Guangzhou City and on subjected to standard calibration procedures and Dinghu Mountain, there was at least a sample per quality control checks as described by Blake et al. day with intensive sampling from March 6 to 9 (2003). The reference materials used were calibrated 2001. On March 6–9 a total of 22 and 23 samples by the standards obtained from static dilutions of were collected in Guangzhou City and on Dinghu primary standards prepared in the same laboratory Mountain, respectively, and the sampling covered (Colman et al., 2001). The analytical accuracy diurnal cycles. At these two sites, sampling was ranged from 2% to 20%. The sampling/analytical performed between 12:00 and 14:00 local standard precisions vary by compounds and by mixing ratios. time except for the diurnal cycle sampling. The Table 1 summarizes the detection limits of the sampling duration for each sample was around halocarbon species, which are considerably lower 2–3 min. In Panyu, the sampling was performed at than the mixing ratios discussed in this study. noon with the help of a needle valve placed in front of the inlet of the canisters. The sampling duration 3. Results and discussion was 1 h. Pre-cleaned and evacuated electropolished 2-L stainless steel canisters from a laboratory of the 3.1. Predominantly anthropogenic halocarbons University of California, Irvine (UC-Irvine) were used for air sample collection. Table 1 summarizes the average mixing ratios of Air samples were also collected in tunnels and halocarbons together with their standard deviations roadside sites heavily impacted by the vehicular for the three ambient monitoring sites. For con- emission in the PRD region and Hong Kong on 2–9 sistency, only the data of daytime (08–16 h) samples June 2000.