Characteristics and Diurnal Variations of Nmhcs at Urban, Suburban, and Rural Sites in the Pearl River Delta and a Remote Site in South China
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ARTICLE IN PRESS Atmospheric Environment 41 (2007) 8620–8632 www.elsevier.com/locate/atmosenv Characteristics and diurnal variations of NMHCs at urban, suburban, and rural sites in the Pearl River Delta and a remote site in South China J.H. Tanga,1, L.Y. Chana, C.Y. Chana, Y.S. Lia,Ã, C.C. Changb, S.C. Liub, D. Wuc, Y.D. Lid aDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, China bResearch Center for Environmental Changes, Academia Sinica, Taipei, Taiwan cInstitute of Tropical and Marine Meteorology, CMA, Guangzhou, China dThe Research Institute of Tropical Forestry, CAF, Guangzhou, China Received 21 November 2006; received in revised form 28 June 2007; accepted 12 July 2007 Abstract The Pearl River Delta (PRD) is one of the most industrialized and urbanized regions in China. With rapid growth of the economy, it is suffering from deteriorating air quality. Non-methane hydrocarbons (NMHCs) were investigated at urban and suburban sites in Guangzhou (GZ), a rural site in PRD and a clean remote site in South China, in April 2005. Additional roadside samples in GZ and Qingxi (QX, a small industrial town in PRD), ambient air samples at the rooftop of a printing factory in QX and exhaust samples from liquefied petroleum gas (LPG)—fueled taxis in GZ were collected to help identify the source signatures of NMHCs. A large fraction of propane (47%) was found in exhaust samples from LPG-fueled taxis in GZ and extremely high levels of toluene (2.0–3.1 ppmv) were found at the rooftop of the printing factory in QX. Vehicular and industrial emissions were the main sources of NMHCs. The effect of vehicular emission on the ambient air varied among the three PRD sites. The impact of industrial emissions was widespread and they contributed greatly to the high levels of aromatic hydrocarbons, especially toluene, at the three PRD sites investigated. Leakage from vehicles fueled by LPG contributed mainly to the high levels of propane and n-butane at the urban GZ site. Ethane and ethyne from long-range transport and isoprene from local biogenic emission were the main contributors to the total hydrocarbons at the remote site. Diurnal variations of NMHCs showed that the contribution from vehicular emissions varied with traffic conditions and were more influenced by fresh emissions at the urban site and by aged air at the suburban and rural sites. Isoprene from biogenic emission contributed largely to the ozone formation potential (OFP) at the remote site. Ethene, toluene and m/p-xylene were the main contributors to the OFP at the three PRD sites. r 2007 Elsevier Ltd. All rights reserved. Keywords: Non-methane hydrocarbons; Source signature; LPG; PRD; South China 1. Introduction ÃCorresponding author. Tel.: +852 2766 6069. E-mail address: [email protected] (Y.S. Li). The Pearl River Delta (PRD) is one of the most 1Now at Yantai Institute of Coastal Zone Research for urbanized and industrialized regions in South China. Sustainable Development, CAS. Accompanying the substantial economic development, 1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.07.029 ARTICLE IN PRESS J.H. Tang et al. / Atmospheric Environment 41 (2007) 8620–8632 8621 large amounts of air pollutants are discharged, ruralsiteinthePRD;aswellasataremotesitein resulting in a rapid deterioration of the overall air South China in April 2005. quality. High levels of carbon monoxide, sulfur dioxide, nitrogen oxides (NOx), ozone (O3) and 2. Experiment volatile organic compounds (VOCs) are frequently found in the PRD (Wang et al., 2005; Zhao et al., 2.1. Sampling sites 2004). Elevated aromatic hydrocarbons were re- ported at roadsides of the PRD cities (Chan et al., Four sites were selected for this study in 2005: 2002a; Wang et al., 2002). The frequency of ozone Guangzhou (GZ), Panyu (PY), Dinghu mountain episodes in the downwind regions, such as Hong (DM) and Jianfeng mountain (JM). Fig. 1 shows Kong has increased significantly (Chan and Chan, their geographical locations and Table 1 describes 2000; Chan et al., 2002b; Wang et al., 2005). the characteristics of the sampling sites. Non-methane hydrocarbons (NMHCs) are key GZ is the capital city of Guangdong Province ozone precursors and play a very important role in with a total population of 7.5 million. It is the tropospheric chemistry. Photochemical reactions of economic and cultural center of the PRD. The NMHCs with NOx result in the formation of ozone sampling site is located in the urban center, and other atmospheric oxidants, which affect the the Dongshan district, and is surrounded by resi- global distribution of hydroxyl radical (OH), and dential buildings and business offices. At 100 m consequently influence the lifetime of other trace distance away from the sampling site to the north species in the troposphere (Poisson et al., 2000). In and the south directions, there are two main roads urban areas, such as Guangzhou and Hong Kong, with very heavy traffic. This site represents a typical ozone formation is VOC limited, as there is GZ urban site, which is influenced by residential sufficient NOx from vehicular exhausts (Wang and traffic emission sources. et al., 2005). Therefore, an effective strategy for PY is a satellite city of GZ with a total population mitigating ozone pollution in urban areas can be of one million in an area of 1300 km2. The sampling obtained by controlling the emission of NMHCs site was located in a suburban environment. This (a subset of VOCs). site is about 20 km from the urban center of GZ to Several studies on NMHCs distribution had been the north, 25 km from Dongguan (a famous conducted in China, especially in South China. A industrial manufactory center of China with about study in 43 Chinese cities indicated that vehicular 6.6 million inhabitants) to the west, 30 km from emissions were the major source of NMHCs in 10 Zhongshan (an important industrial city in PRD cities, while coal and biofuel combustions were the with 2.4 millions inhabitants) to the south. There is major sources in 15 other cities (Barletta et al., no obvious anthropogenic source nearby except for 2005). Another study of two urban sites in Hong a road about 50 m to the south. Air samples were Kong showed that vehicular emission, solvent use collected at the rooftop of an environmental and liquid petroleum gas (LPG) or natural gas (NG) monitoring chamber (about 4 m above ground). leakage were the major sources of NMHCs (Guo DM is located in the middle of Guangdong et al., 2004). However, at rural sites in Hong Kong, Province in South China and is surrounded by the NMHC sources were highly variable. For air tropical forest. It is about 85 km to the west of GZ masses transported through the Hong Kong urban and 18 km to the northeast of Zhaoqing (a less area, local vehicular emissions were still the domin- industrialized city compared with other cities in ant source, while for air masses transported through PRD with about 3.7 millions inhabitants). There is a the PRD area, local industrial emissions were the small town (the Guicheng district, with a population major source (Guo et al., 2006). A study of NMHCs of 20,000) and a highway near the sampling site in the PRD industrial, industrial-urban, and in- about 3 km to the south. The sampling site is dustrial-suburban atmospheres showed that indus- located at the hilltop in the Dinghushan Biosphere trial emissions had great influence on the ambient Reserve, which is a station of the Man and the levels of NMHCs (Chan et al., 2006). Biosphere Programme of the United Nations In this study, we have presented a snapshot of Educational, Scientific and Cultural Organization. atmospheric NMHCs in the fast urbanizing and JM is situated on the southeast coast of Hainan industrializing PRD region. Air samples were collected Island and is about 120 km from Sanya (the second at an urban and a suburban site of Guangzhou and a largest city in Hainan Province, with a population ARTICLE IN PRESS 8622 J.H. Tang et al. / Atmospheric Environment 41 (2007) 8620–8632 Fig. 1. Locations of the four sampling sites in the PRD and South China. Table 1 Characteristics of the four sampling sites Site Abbreviation Location Altitude, Sampling periods Site characteristics m asl Guangzhou GZ 23.081N, 88 16–22 April 2005 Urban site, at the rooftop of 113.181E a 21-storey building Panyu PY 22.561N, 16 16–22 April 2005 Suburban site, 4 m above the 113.191E ground Dinghu mountain DM 23.101N, 320 16–22 April 2005 Rural site, at the top of a hill 112.321E Jianfeng mountain JM 18.401N, 820 7–13 and 16–18 Remote site, at the rooftop 108.491E April 2005 of a 2-storey building of 0.5 million) and 315 km from Haikou, the capital also collected at the rooftop of a printing factory city of Hainan province. The mountain faces the (a three-storey building) between 14:45 and 15:00 local South China Sea in the south and west directions. time in QX to obtain the source signature of NMHCs The sampling site was situated within the Jianfen- from a particular industry. QX is a small industrial gling National Reserve, which is the second largest town with many factories. Later, to study the impacts tropical rain forest in China with a total area of of LPG-fueled vehicles, two exhaust samples from 475 km2. The sampling site was surrounded by LPG-fueled taxis were collected on 23 June 2006. several hills with elevations exceeding 1000 m asl.