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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

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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. The five tunnels sampled included one in for Guangzhou City and Dinghu Mountain were Guangzhou City (Zhujiang Tunnel), one in rural used. The readers are reminded that the 2001 data Guangzhou with trans-provincial traffic (Baiyun set is not directly comparable with that of 2004 due Tunnel), one in Shenzhen city (Wu Tong Shan to differences in sampling seasons and years. Also Tunnel) and two in urban Hong Kong (Cross shown are the average mixing ratios of halocarbons Harbour Tunnel and West Harbour Tunnel). Four for the tunnel and roadside samples. In calculating samples were collected in roadside sites in the the average mixing ratios, a tunnel sample with central business districts of Guangzhou City exceptionally high levels of all species was deleted. (a road with six lanes in the front door of We also included in Table 1 the background mixing Zhongshan University campus) and Shenzhen ratios of the boundary layer air of the western (Lowu Train Station with heavy traffic). Tunnel North Pacific along the East Asian coast, which air was sampled at about 1.6 m above ground represent the 25 percentile values measured onboard surface onboard of a vehicle driven along the of a DC aircraft during TRACE-P period (spring) normal traffic of the tunnels by penetrating the in 2001 (Barletta et al., 2005). The mixing ratios of 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7334 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345

Table 1 Mixing ratios of halocarbons (pptv, 1 part in 1012 by volume)a

LODb Guangzhou City Panyu Dinghu Tunnels and Background Mountain roadsidesc

Western Northern Mean s Mean s Mean s Mean s Pacificd hemisphere

CFC-12 10 720 100 820 660 580 20 1120 310 537 CFC-11 1 361 95 302 27 291 16 329 85 260 CFC-113 1 97 13 97 16 93 8 191 31 79 CFC-114 1 16 1 16 0 16 0 14 1 14 Halon-1211 0.05 128 167 16 19 18 16 25 29 4.3 4e Halon-2402 0.05 0.5 0.1 NM NM 0.5 0.2 0.5 0.1 0.51 HFC-134a 1 36 20 49 14 19 8 NM NM 16 HCFC 22 1 553 418 274 62 205 46 NM NM 154 HCFC-142b 1 90 150 21 3 45 123 NM NM 14 14–15f HCFC-141b 1 46 46 51 24 21 5 NM NM 15 g CHCl3 0.1 181 491 52 15 33 10 51 20 11 600 CH3CCl3 1 93 51 29 6 60 21 114 144 40 CCl4 0.01 138 48 129 35 123 29 274 351 99 CH2Cl2 0.01 NM NM 648 399 NM NM 812 601 35 h C2HCl3 1 234 261 656 566 84 114 NM NM 0.9 3.5 i C2Cl4 0.05 268 374 93 92 48 49 798 1380 7.6 7–26 CH3Cl 5 1210 740 1140 340 1010 290 NM NM 546 CH3Br 1 18 6 16 4 17 10 17 10 8.7 j CH3I 0.01 4.2 4.1 2.6 0.7 2.5 1.4 1.65 0.42 0.4 0.12–2.0 CH2Br2 0.01 1.3 0.3 1.0 0.1 1.4 0.3 2.13 1.55 CHBrCl2 0.01 1.6 3.2 NM NM 0.5 0.3 NM NM CHBr3 0.01 5.3 13.5 2.1 0.5 2.1 1.5 21.1 36.3 1.1 C2H5Cl 0.05 98.5 219.5 NM NM 47.1 48.0 NM NM CH2ClCH2Cl 0.05 37 43 169 225 15 5 NM NM aNM: no measurement; daytime data: 8–16 h. bLOD: limit of detection. cA sample with extreme values was deleted. d25 percentile of TRACE-P western Pacific below 1500 m, Barletta et al. (2005). eButler et al. (1998). fwww.cmdl.noaa.gov/hats/insitu/cats/cats_conc.html. gKhalil and Rasmussen (1999). hQuack and Suess (1999). iWang et al. (1995). jCarpenter et al. (1999).

most halocarbons in the relatively rural site Dinghu higher mixing ratios on Dinghu Mountain. Table 2 Mountain, where no apparent anthropogenic emis- compares the mixing ratios of selected halocarbons sion source is observed, were much elevated when measured in Guangzhou City and Panyu to those compared with the background levels over the reported for Bristol, England (Rivett et al., 2003), western Pacific and East Asian coast, especially Athens, Greece (Glavas and Moschonas, 2002), for C2HCl3,CH3I, C2Cl4, Halon-1211, HCFC-142b Philadelphia and Las Vegas, USA, and Marseille, and CHCl3. The average mixing ratios of these France (Barletta et al., 2005 and references therein). species of predominantly anthropogenic (except We noted that with the exception of 1,2-dichlorote- CH3I) were 94, 6, 6, 4, 3 and 3 times, respectively, trafluoroethane (CFC-114, CClF2CClF2) in Mar- of the respective western Pacific background mixing seille and 1,1,1-trichloroethane (CH3CCl3)in ratios. They are also higher than the respective Panyu, all species had higher mixing ratios in background levels of the Northern Hemisphere. Guangzhou City and Panyu. Other species, except dibromotetrafluoroethane Trichloroethene (C2HCl3), C2Cl4 and CHCl3 (Halon-2402, CBrF2CBrF2), also had noticeable have industrial applications mainly as solvents and 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 7335

Table 2 Mixing ratios of selected halocarbon levels measured in cities around the world (pptv)

CFC-12 CFC-11 CFC-113 CFC-114 CHCl3 CH3CCl3 CCl4 CH2Cl2 C2HCl3 C2Cl4

Chinaa 564 284 79 14 50 52 121 455 28 201 Bristol, Englandb 566 301 45 54 98 73 37 Athens, Greecec 60 180 Philadelphia, USAd 549 272 83 15 45 102 Las Vegas, USAd 565 262 82 15 42 99 Marseille, Francee 555 286 83 24 50 103 Guangzhou, China 720 361 97 16 181 93 138 NMf 234 268 Panyu, China 820 302 97 16 52 29 129 648 656 93

aJanuary–February, 2001 (Barletta et al. 2005; 45 cities average). bAugust–September, 2000 (Rivett et al., 2003). cJuly–August, 2000 (Glavas and Moschonas, 2002). dFebruary, 2001 (Barletta et al. 2005). eJune–July, 2001 (Barletta et al. 2005). fNM: no measurement. degreasers or in some cases for production of CFC mixing ratios in Guangzhou City (97 and 720 pptv, and HCFCs (Sturrock et al., 2002; Altshuller, 1976). respectively). Vehicular exhaust, evaporation and They are often regarded as tracers for identifying leakage of chemicals from vehicular fuel, goods the air with urban/industrial influences (Atlas et al., onboard of vehicles and the air conditioning 1992; Blake et al., 1997; Schneider et al., 1998). systems of vehicles and the tunnels are among the Halon-1211 and Halon-2402 are widely used fire most prevalent sources of halocarbons in the fighting agent in fire suppression systems. China is roadside and tunnel microenvironments. CFC-11 one of the few countries still producing Halon-1211 and CFC-12 have been used extensively as aerosol- (UNEP, 2002). HCFC-142b is an effective replace- spray propellants, foam-blowing agents, solvents ment chemical for CFC-12 and more recently for and refrigerants in the air conditioning systems. HCFC-141b (1,1-dichloro-1-fluoroethane, C2H3FCl2). CFC-113 is used for precision cleaning of sensitive The high levels of these halocarbons measured equipment, electronics and liquid oxygen systems as suggest that the PRD air is significantly affected by well as for verifying the cleanliness level of equip- the halocarbon emissions from the urban and ment after it has been cleaned in industrial processes industrial activities. An exception is Halon-2402. The (Morris, 1996). The high CFC-11 and CFC-12 can mixing ratios of Halon-2402 on Dinghu Mountain be explained by their common usage as solvents and and that of Guangzhou City are close to the refrigerants in the tunnels. background values for the western Pacific (0.51 pptv) and the Northern Hemisphere (0.45 pptv) (Butler 3.2. Mixed anthropogenic/biogenic halocarbons et al., 1998)(Table 1). These suggested that there is no significant source of Halon-2402 in the PRD as Another interesting feature we noted is that the compared to the whole western Pacific and East Asian measured mixing ratios of methyl halides were coast. elevated compared to the background mixing ratios We also noted that the average mixing ratios of of the western Pacific (Table 1). As mentioned CFC-12, CFC-113 for the tunnel and roadside earlier, the average mixing ratio of CH3I (2.5 pptv) samples were noticeably higher than those for the on Dinghu Mountain is 6 times of the western ambient samples in Guangzhou City, Panyu and Pacific background of 0.4 pptv. Even higher average Dinghu Mountain (Table 1). This suggested that mixing ratio of 4.2 pptv was found in Guangzhou there exists significant sources of these species in the City. These results suggested that there are strong tunnel and roadside environments. In fact, a regional sources of methyl halides in the PRD detailed examination of the tunnel and roadside region. We also noted that the mixing ratios of samples unveiled that the mixing ratios of CFC-113 CH3I and CH3Cl decreased from Guangzhou City (166–278 pptv) and CFC-12 (784–1650 pptv) of all to Dinghu Mountain (Table 1) suggesting that there 12 samples exceeded their corresponding average are significant sources of CH3I and CH3Cl in the 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7336 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345

urban areas of the PRD. Methyl chloride (CH3Cl) In Guangzhou City, CH3Cl correlated well with and CH3Br have highly unbalanced global budget ethyl chloride (C2H5Cl), and CH3Br, CHBrCl2, with known sinks outweighing known sources CHBr3,CH3I, CHCl3 and carbon disulfide (CS2) (Butler, 2000; WMO, 2002). Methyl chloride has (Table 3). It also showed fairly good correlations oceanic and industrial sources (Blake et al., 1996). with ethane (not shown), CH4, OCS, CH2Br2 and However, biomass/biofuel burnings, in particular hexane (not shown). On Dinghu Mountain, CH3Cl coal burning, are believed to be the major sources of correlated well with C2H5Cl, CH2Br2 and CH3I, CH3Cl in China (Blake et al., 1997, 2003). Methyl and fairly good with CHBr3 and CFC-11, CFC-113, bromide has abundant sources from agricultural Halon-1211 and toluene (not shown) (Table 3). In use, litter and leaded gasoline combustion, biomass Panyu, it correlated well with CH3Br and showed burning, salt marshes and oceans (Yokouchi et al., fairly good correlations with OCS, CFC-114 and 2002 and references therein). High levels of CH3Cl CO. The major sources of C2H5Cl, CHCl3, CFC-11, were also reported for Linan in spring by Wang et CFC-113 and Halon-1211 are associated with al. (2002a, b). Wang et al. suggested that the industrial activities. CO and ethane are general springtime agricultural biomass/biofuel burning combustion products. Coal burning is an important activities in the Yangzhi River Delta may be the source of OCS and CS2. Methyl iodide (CH3I) has a cause of the high CH3Cl observed in Linan. predominant oceanic source (Cox et al., 2004). In the PRD, burnings of biomass and biofuels CHBr3 and CH2Br2 have a marine source (Zhou et such as agricultural residues, wood and charcoal are al., 2005). The correlations between CH3Cl and seldom observed in the major cities including these species tend to suggest that it is emitted from Guangzhou City, Panyu and Zhaoqing where some co-located industrial and combustion sources Dinghu Mountain is located, although some small- (Fig. 2 and Table 3). scale open burnings of agricultural residues and The PRD region is situated in the subtropics domestic waste are still observed in the rural areas and it has a variety of terrestrial–coastal ecosys- of Zhaoqing, like other relatively less urbanized and tems such as coastal freshwater wetlands, marshes, industrialized regions of Guangdong province. fish ponds and an extensive river network extend- Therefore, we believe that biomass/biofuel burnings ing from the western side of Hong Kong along (excluding coal burning) in the PRD, in particular the Pearl River Estuary and Pearl River to the Guangzhou City, may not be the major sources of inlands of Guangdong province (Fig. 1). Thus, the elevated CH3Cl and CH3Br observed. Coal it is reasonable to assume that large amounts burning is one of the major energy sources in of methyl halides were emitted from these ecosys- Guangdong province and the PRD. It accounted for tems. Carpenter et al. (2003) found a positive 27% of the total energy supply of Guangdong correlation between CH2Br2 and CHBr3 in the province in 2003 (GTRDC, 2005). Hence, it is air masses with recent marine influences and stated reasonable to believe that coal combustion is an that they have a common biological source. Zhou important source of the elevated CH3Cl and CH3Br et al. (2005) observed a similar correlation with a observed. However, the major coal combustion linear CH2Br2–CHBr3 correlation slope of 0.12 activities in the PRD are confined to large-scale for the samples collected at Great Bay, New power plants with air pollution control facilities. Hampshire. In this study, we also found good Thus, the contribution of coal burning to CH3Cl in correlations between CH2Br2 and CHBr3 on Din- the PRD may not be as important as in northern ghu Mountain and Guangzhou City and the China, where smaller scale burning activities are still respective CH2Br2–CHBr3 correlation slopes on prevalent in the domestic and commercial sectors. Dinghu Mountain (0.17) and Guangzhou City In fact, Qin and Chan (1993) has found in the early (0.15) (Fig. 3) are close to that at Great Bay. In 1990s that vehicular emissions have replaced coal addition, fairly to good correlations were observed burning emissions to be the main contributor to the between CH2Br2 and CHBr3, and CH3I(Fig. 3), poor air quality in Guangzhou City. Yet, the CHBr3 and CH3Cl (Table 3). These evidences measured mixing ratios of CH3Cl decreased from tend to suggest that the emissions from the Guangzhou City to Panyu and Dinghu Mountain terrestrial–coastal ecosystems such as Dinghu Lake suggesting there are some other important factors within the Dinghu Botanical Garden may have that had contributed to the higher levels of CH3Cl contributed to the high levels of methyl halides in Guangzhou City. measured. 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 7337

Table 3 Spearman’s correlation coefficient (Rs)

Guangzhou City Panyu Dinghu Mountain

CH3Cl CH3Br CH3ICH3Cl CH3Br CH3ICH3Cl CH3Br CH3I

CO 0.21 0.46 0.59 0.61 0.56 0.27 0.21 0.67 0.76

CH4 0.47 0.63 0.65 0.22 0.59 0.08 0.15 0.65 0.65 OCS 0.51 0.64 0.74 0.68 0.78 0.06 0.36 0.55 0.64 DMS 0.18 0.51 0.61 0.21 0.20 0.79 0.38 0.14 0.44

CS2 0.70 0.63 0.47 0.39 0.40 0.15 0.10 0.25 0.25 CFC-12 0.10 0.23 0.34 0.29 0.08 0.02 0.24 0.54 0.53 CFC-11 0.07 0.34 0.46 0.17 0.11 0.73 0.48 0.65 0.63 CFC-113 0.23 0.59 0.60 0.47 0.34 0.54 0.47 0.67 0.67 CFC-114 0.16 0.04 0.26 0.67 0.62 0.06 0.08 0.01 0.03 Halon-1211 0.21 0.32 0.39 0.22 0.58 0.21 0.48 0.74 0.71 Halon-2402 0.25 0.39 0.44 0.27 0.39 0.38 HFC-134a 0.11 0.32 0.37 0.10 0.43 0.23 0.18 0.35 0.24 HCFC 22 0.08 0.37 0.38 0.15 0.35 0.08 0.40 0.77 0.73 HCFC-142b 0.19 0.04 0.15 0.14 0.20 0.46 0.25 0.23 0.26 HCFC-141b 0.29 0.51 0.53 0.36 0.13 0.67 0.39 0.78 0.71

CHCl3 0.70 0.75 0.63 0.07 0.39 0.02 0.18 0.66 0.58 CH3CCl3 0.30 0.62 0.56 0.18 0.19 0.69 0.40 0.79 0.69 CCl4 0.20 0.41 0.40 0.29 0.40 0.28 0.36 0.64 0.57 CH2Cl2 0.49 0.69 0.59 0.02 0.08 0.18 0.07 0.29 0.07 C2HCl3 0.20 0.56 0.54 0.44 0.49 0.29 0.37 0.76 0.76 C2Cl4 0.20 0.38 0.37 0.43 0.48 0.34 0.21 0.75 0.67 CH3Cl 1.00 0.74 0.66 1.00 0.73 0.16 1.00 0.49 0.62 CH3Br 0.74 1.00 0.83 0.73 1.00 0.17 0.49 1.00 0.80 CH3I 0.66 0.83 1.00 0.16 0.17 1.00 0.62 0.80 1.00 CH2Br2 0.48 0.67 0.57 0.40 0.01 0.47 0.66 0.54 0.58 CHBrCl2 0.73 0.77 0.71 0.35 0.46 0.48 CHBr3 0.72 0.67 0.55 0.58 0.44 0.30 0.59 0.68 0.75 C2H5Cl 0.78 0.40 0.35 0.69 0.45 0.46 CH2ClCH2Cl 0.38 0.41 0.31 0.26 0.47 0.18 0.03 0.53 0.46

We also noted from Table 1 that the average slope of these samples was much lower (0.04) mixing ratios of CH2Br2 and CHBr3 for the tunnel than those on Dinghu Mountain and Guangzhou and roadside samples were high. In fact, a total of City. eight and nine samples had CH2Br2 (1.36–324 pptv) and CHBr3 (6.1–4896 pptv) mixing ratios exceeding 3.3. Elevated mixing ratio episodes the respective average values in Guangzhou City (1.3 and 5.3 pptv, respectively). In these tunnel and We observed elevated halocarbon mixing ratios in roadside samples, CH2Br2 and CHBr3 showed Guangzhou City and on Dinghu Mountain on 6–9 strong correlation with each other with a Spear- March 2001 during the intensive sampling. Fig. 4 man’s correlation coefficient (Rs) of 0.89. They also shows the time series of mixing ratios of selected showed good correlations with CH3Br (Rs ¼ 0.84 halocarbons in this period. Elevated mixing ratios and 0.73, respectively) and to a less extent C2Cl4 were first observed in the early morning of 6 March (Rs ¼ 0.65 and 0.55, respectively). These correla- on Dinghu Mountain. There was no sample in tions suggested that they were emitted from the Guangzhou City on that day. In the morning of 7 same source, most probably vehicular exhaust, as March most species especially those associated with some bromine compounds are added to leaded industrial emissions such as CFCs (except CFC- gasoline (Yokouchi et al., 2000) and leaded gaso- 114), Halons, HCFCs (except HCFC-142b) and line is the prevalent vehicular fuel used in the chlorinated hydrocarbons showed significant in- PRD before 2002. The CH2Br2–CHBr3 correlation creases to reach their peaks at noon (12:00) in 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7338 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345

Tunnels and roadside sites 1.0 CFC-12 CFC-113 0.8

0.6

Rs 0.4

0.2

0.0 I 4 3 3 3 2 4 2 3 Br 3 Cl Cl Br 2 2 2 CCl CH CCl 3 C CHCl CH CHBr CFC-12 CFC-11 CH CH CFC-113 CFC-114 CH Halon-1211 Halon-2402

Tunnels and roadside sites 1.0 CHBr3 CH2Br2 0.8

0.6

Rs 0.4

0.2

0.0 I 4 3 3 3 2 2 4 3 Br 3 Cl Cl Br 2 2 2 CCl CH CCl 3 C CHCl CH CHBr CFC-12 CFC-11 CH CH CFC-113 CFC-114 CH Halon-1211 Halon-2402

Fig. 2. Spearman’s correlation coefficients of CFC-12, CFC-113, CHBr3 and CH2Br2 for the roadside sites and tunnels.

Guangzhou City and at noon or early afternoon on occurrences of the peak mixing ratios of various Dinghu Mountain. The measured mixing ratios of halocarbons probably reflects the fact that there are C2HCl3,CH3I, C2Cl4 and Halon-1211 reached 772, a variety of emissions sources for the wide spectrum 8.1, 2182 and 671 pptv, respectively, in Guangzhou of halocarbons. City and 176, 4.5, 129 and 48 pptv, respectively, on Fig. 6 shows the flow pattern at 850 hPa altitude Dinghu Mountain. These values are much elevated at 00UTC (08:00 local standard time) on 6–9 March when compared with the respective average values for the PRD and its neighboring regions in (Table 1). Most halocarbons showed decreases in Guangdong province simulated from the Pennsyl- mixing ratios until the late morning of 9 March vania State University/National Center for Atmo- when elevated levels were observed again in spheric Research (NCAR) mesoscale model (MM5). Guangzhou City. In these episodes, we also The model was configured to have a horizontal observed simultaneous increases of CH3I, CH3Br resolution of 9 km based on a domain, which covers and other species including CH2Br2, CHBrCl2, most of China and the western Pacific, 23 vertical CHBr3 and DMS (Fig. 5), which have strong layers and a time step of 27 s for iteration. A high- sources from the ocean and terrestrial-coastal resolution Blackdar planetary boundary layer ecosystems. However, we noted that some halocar- scheme, a RRTM longwave radiation scheme and bons did not show much enhancement and their a Reisner graupel moisture scheme (Reisner 2) were peaks did not occur at the same time as the other used. It used the reanalysis data from the National species. For instance, the maximum mixing ratio of Centers for Environmental Prediction/NCAR HCFC-142b was found in the morning of 8 (NCEP/NCAR) as input. The data have a resolu- March on Dinghu Mountain while the maxi- tion of 2.51 2.51. The simulated flow patterns mum mixing ratio of CH3Cl was found in the suggested that there was a change of mesoscale air morning of 9 March. The variability in the flow due to the changes in synoptic meteorology 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 7339

Guangzhou City CH2Br2 CH3I 2.5 25 y = 0.15x + 0.93 2.0 Rs = 0.71 20 2

1.5 15 I 3 Br 2

1.0 10 CH CH

0.5 y = 1.15x + 0.77 5 Rs = 0.55 0.0 0 0 1 23456

CHBr3

Guangzhou City CH Br 2.5 2 2

y= 0.02x + 1.24 2.0 Rs = 0.57

2 1.5 Br 2 1.0 CH

0.5

0.0 0 510152025

CH3I

Dinghu Mountain CH2Br2 CH3I 3.0 9.0

y = 0.17x + 0.98 Rs = 0.69 2.0 6.0 2 I 3 Br 2 CH CH 1.0 3.0 y = 0.72x + 0.22 Rs = 0.75

0.0 0.0 0 396

CHBr3

Dinghu Mountain CH2Br2 3.0

y = 0.13x + 0.99 Rs = 0.58 2.0 2 Br 2

CH 1.0

0.0 0 369

CH3I

Fig. 3. Spearman’s correlation between CH2Br2, CHBr3 and CH3I. 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7340 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345

from a general southerly wind on 6 and 7 March to million), Dongguang and others due to a general a northerly on 8 March and finally an easterly on 9 southerly or easterly wind before reaching Guangz- March in the Guangdong region. The flow patterns hou City and Dinghu Mountain on 6, 7 and 9 suggested that the polluted air masses had traveled March. The air masses originated from the coastal across Hong Kong (a population of 6.8 million), the region of southeast China and believed to have PRD cities of Shenzhen (a population of 4.3 picked up huge amounts of anthropogenic emissions

Guangzhou City CFC-12 CFC-11 CFC-114 CFC-113 1000 150

500 75 CFC-12, CFC-11 CFC-114, CFC-113 0 0

HCFC-22 HCFC-142b HFC-134a HCFC-141b 1500 150

750 75

0 0 HCFC-22, HCFC-142b HFC-134a, HCFC-141b

Halon-1211 Halon-2402 800 1.0

400 0.5 Halon-1211 Halon-2402

0 0.0

CHCl3 C2Cl4 CH3Cl CCl4 3200 400 Cl 3 , CH 4 4

Cl 1600 200 2 CCl , C 3

CHCl 0 0

C2HCl3 CH2ClCH2Cl CCl3CH3 800 400 3 CH 3 3

400 200 Cl,CCl HCl 2 2 C ClCH 2 CH 0 0 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 (a) 6-9 March, 2001

Fig. 4. Mixing ratios from 6 to 9 March 2001 (pptv). 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 7341

Dinghu Mountain CFC-12 CFC-11 CFC-114 CFC-113 1000 150

500 75 CFC-12, CFC-11 0 0 CFC-114, CFC-113

HCFC-22 HCFC-142b HFC-134a HCFC-141b 1000 40

500 20

0 0 HCFC-22, HCFC-142b HFC-134a, HCFC-141b

Halon-1211 Halon-2402 80 0.6

40 0.3 Halon-1211 Halon-2402

0 0.0

CH Cl CCl C Cl CHCl 1800 3 4 2 4 3 200 3 Cl 3 900 100 , CHCl , CH 4 4 Cl 2 CCl C

0 0

C2HCl3 CCl3CH3 CH2ClCH2Cl 500 120 3 CH 3 3

250 60 Cl, CCl HCl 2 2 C ClCH 2

0 0 CH 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 (b) 6-9 March, 2001

Fig. 4. (Continued)

when they passed through the urban and industrial suggest that the elevated mixing ratios of CH3I, zones of the above cities and thus resulted in elevated CH3Br, CH2Br2,CHBrCl2,CHBr3 and DMS on 7 mixing ratios of most halocarbons. Also, the oceanic March were due to transports of these species from air had passed over the Pearl River Estuary and Pearl the ecosystems of the coastal regions of PRD Estuary River before it reached Guangzhou City, Panyu and and Guangdong. These species were then mixed up Dinghu Mountain. The above evidence tends to with the halocarbons of pure anthropogenic nature 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7342 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345

Guangzhou City

CHBr3 CHBrCl2 CH2Br2 10 3.0 2 2 Br

5 1.5 2 , CHBrCl 3 CH CHBr 0 0.0

CH3Br CH3I DMS 30 120 I 3

15 60 Br, CH DMS 3 CH

0 0 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 6-9 March, 2001

Dinghu Mountain

CHBr3 CHBrCl2 CH2Br2 4.0 1.6 2 2 Br

2.0 0.8 2 , CHBrCl 3 CH CHBr 0.0 0.0

CH3Br CH3I DMS 22 120 I 3

11 60 Br, CH DMS 3 CH

0 0 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 6-9 March, 2001

Fig. 5. Mixing ratios of CHBr3,CH2BrCl2,CH2Br2,CH3Br, CH3I and DMS from 6 to 9 March 2001 (pptv).

during their transport to the sampling sites. This may bons when compared with the regional mixing explain why CH3Cl, CH3Br and CH3I had simulta- ratios of the western Pacific and East Asian coast, neous good correlations with many other species of and the background levels of the Northern Hemi- man-made and natural origins. sphere. The results suggested that there are sig- nificant sources of halocarbons, in particular, 4. Conclusions C2HCl3,CH3I, C2Cl4, Halon-1211, HCFC-142b and CHCl3 in the PRD. The results on the other The results of this study revealed elevated hand indicated that there is no significant source of regional mixing ratios of many species, including Halon-2402. Our results also suggested that there CFCs, HFCs, HCFCs, Halons and other halocar- are significant sources of CFC-12, CFC-113, 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 7343

00Z06MAR2001 00Z07MAR2001

27N 27N

26N 26N

25N 25N

24N 24N Guan gzhou City Guan gzhou City

23N 23N Panyu Dinghu Panyu Dinghu

22N Mountain 22N Mountain

21N 21N

20N 20N

110E 111E 112E 113E 114E 115E 116E 117E 118E 119E 110E 111E 112E 113E 114E 115E 116E 117E 118E 119E

10 10

00Z08MAR2001 00Z09MAR2001

27N 27N

26N 26N

25N 25N

24N 24N Guan tgzhou City Guan gzhou City

23N Panyu 23N Dinghu Dinghu Panyu

22N Mountain 22N Mountain

21N 21N

20N 20N

110E 111E 112E 113E 114E 115E 116E 117E 118E 119E 110E 111E 112E 113E 114E 115E 116E 117E 118E 119E

10 10

Fig. 6. Flow pattern at 850 hPa on 6–9 March 2001 for the PRD and its neighboring regions simulated by MM5.

CH2Br2 and CHBr3 in the tunnels and roadside still have very high mixing ratios in the PRD. China sites, and the excessive CH2Br2 and CHBr3 are is required to reduce 50% of the 1995–1997 average related to vehicular exhaust emissions. High levels baselines of CFC production and consumption by of methyl halides: CH3Cl, CH3I and CH3Br, and 2005. Based on the results of this study, these CH2Br2, CHBrCl2,CHBr3 and DMS were simulta- requirements have not been fully achieved for many neously observed in the oceanic air masses that species including CFC-12 in 2004 in the PRD originated from the coastal areas of Guangdong region. province and had passed over the Pearl River Estuary and Pearl River. Correlation evidences Acknowledgments suggested that emissions from the coastal territorial ecosystems of the PRD are important sources of This study is supported by research grants from methyl halides, CH2Br2, CHBrCl2, CHBr3 and the Research Grant Council of the Hong Kong DMS observed. In conclusion, we found that while Special Administrative Region (PolyU 5037/00E, some halocarbons under the Montreal Protocol and 5048/02E) and The Hong Kong Polytechnic its Amendments are decreasing, many other species University (A-502 and A-504). We acknowledge 中国科技论文在线 http://www.paper.edu.cn ARTICLE IN PRESS 7344 C.Y. Chan et al. / Atmospheric Environment 40 (2006) 7331–7345

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