Long-range transport of polycyclic aromatic hydrocarbons from China to Japan

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Atmospheric Environment 41 (2007) 2710–2718 www.elsevier.com/locate/atmosenv

Long-range transport of polycyclic aromatic hydrocarbons from China to Japan Xiao-Yang Yanga,, Yumi Okadaa, Ning Tanga, Siori Matsunagaa, Kenji Tamurab, Jin-Ming Linc, Takayuki Kamedaa, Akira Toribaa, Kazuichi Hayakawaa a

Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan b National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba 305-8506, Japan c Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China Received 26 July 2006; received in revised form 21 November 2006; accepted 27 November 2006

Abstract Airborne particulate matter was collected at Wajima, on the Noto Peninsula, Ishikawa, Japan by a high-volume air sampler with a quartz filter every week from 17 September 2004 to 16 September 2005. Polycyclic aromatic hydrocarbons (PAHs) extracted from filters were analyzed by HPLC with fluorescence detection. The atmospheric concentrations of PAHs at Wajima were higher during the heating period of China (when coal is burned for heat) than during the no-heating period. A meteorological analysis indicated that the air samples collected in that heating period at Wajima were transported mainly from Northeast China over the Japan Sea. Principal component analysis of nine PAHs indicated a Chinese origin of the PAHs. These results strongly suggest that the high-level PAHs detected at Wajima were the result of long-range transport from China. r 2006 Elsevier Ltd. All rights reserved. Keywords: PAHs; Airborne particulate matter; Long-range transport; Principal component analysis; China; Japan

1. Introduction In East Asia, which has been undergoing a rapid increase of population and economic development, large amounts of pollutants are released into the air and water. For example, sulfur dioxide emitted from China is transported by the northwest wind in winter season and causes acid rain or acid snow in Japan (Uno et al., 1997). Asian dust (also called Kosa or yellow sand) is also transported from the Corresponding author. Tel.: +81 76 234 4413; fax: +81 76 234 4456. E-mail address: [email protected] (X.-Y. Yang).

1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.11.052

Asian Continent to Japan in the winter and spring seasons (Iwasaka et al., 1983). These facts suggest that other pollutants also might be transported to Japan, which is in the path of winds leaving the Asian Continent. Among the pollutants in the atmosphere, several polycyclic aromatic hydrocarbons (PAHs) and nitropolycyclic aromatic hydrocarbons (NPAHs) are carcinogenic or mutagenic (Ames et al., 1975; Epstein et al., 1979) or have endocrine-disrupting activity (Kizu et al., 2000). PAHs and NPAHs are released in the exhaust from the combustion of petroleum, coal and wood. Additionally, several NPAHs such as 2-nitrofluoranthene and 2-nitropyrene are subsequently

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formed by the reaction of PAHs and NOx in the air (Atkinson et al., 1990; Murahashi et al., 1999). We previously reported that the main contributors to the atmospheric PAHs and NPAHs in Japanese cities (Tokyo, Sapporo and Kanazawa) and Seoul, Korea, were automobiles, especially diesel-engine vehicles, while in Vladivostok, Russia, and Shenyang, Fushun and Tieling, China, they were coal combustion processes (Tang et al., 2002, 2005a, b; Kakimoto et al., 2000, 2002; Hattori et al., 2007). Atmospheric concentrations of PAHs were 3–52 times higher in Chinese and Russian cities than in Japanese and Korean cities (Tang et al., 2005a). The concentration ratios of NPAH to PAH ([NPAH]/[PAH]) of Chinese and Russian cities were much smaller than those of Japanese and Korean cities except for Kitakyushu, Japan, whose value was similar to the values of Chinese cities (Tang et al., 2005a). China has the highest coal consumption in the world and generates over 75% of its energy from coal (Chen et al., 2005). However, in spite of the much higher concentration of atmospheric PAHs in China than in Japan, there has been no report concerning the long-range transport of atmospheric PAHs from China to Japan. The goal of this study was to determine whether PAHs from China are transported long distances to Japan over the Japan Sea. For our collection site, we chose Wajima, on the Noto Peninsula because it is less populated, has no nearby major sources of PAHs, and is in the path of winter northwest winds and year-round west jet stream that blow from China.

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2. Experimental 2.1. Sampling Fig. 1 shows the location of sampling sites. Airborne particulate matter were collected at Wajima Air Monitoring Station (Nisifuta-machi, Wajima City, Ishikawa Prefecture, Japan), which is located on the Noto peninsula 2.1 km south of the Japan Sea coast. The elevation of the sampling site is about 60 m. This station is the former National Wajima Acid Rain Monitoring Station of the Ministry of the Environmental Agency, Japan. No major emission sources of PAHs are near the station. Airborne particulate matter was collected by a high volume air sampler (AH-600, Shibata Japan) with a quartz filter (8 cm  10 cm, 2500QATUP, Pallflex Products, Putnam, CT, USA) at a flow rate of 700 L min1 continuously from 17 September 2004 to 16 September 2005. A new filter was installed every week. The used filter was stored in a freezer (20 1C) until pretreatment. 2.2. Chemicals An EPA 610 PAHs mix containing fluoranthene (FR), pyrene (Pyr), benz[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthrene (BbF), benzo[k]fluoranthrene (BkF), benzo[a]pyrene (BaP), benzo[ghi]perylene (BgPe) and indeno[1,2,3-cd]pyrene (IDP) was purchased from Supelco (Bellefonte, PA, USA). All other chemicals used were of analytical reagent grade.

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2.3. Pretreatment and analysis of samples The filters were cut into small pieces and the pieces were placed in a flask. Pyr-d10 and BaP-d12 were added to the flask as internal standards for PAHs and then the cut filters were extracted ultrasonically for 20 min twice with benzene/ethanol (3:1, v/v). After filtration, a part of the solution was evaporated to dryness. The residue was dissolved in acetonitrile, and an aliquot (20 mL) of this solution was analyzed by HPLC with fluorescence detection. For separating PAHs, a reversed-phase column (Inertsil ODS-P, 4.6 i.d.  250 mm, GL Sciences Inc., Tokyo, Japan) was used with an acetonitrile/ water gradient. The flow rate was 1 mL min1. The time program of the fluorescence detector was set to detect at the optimum excitation and emission wavelengths for each PAH. Other conditions were the same as those in our previous report (Tang et al., 2002). The detection limits ðS=N ¼ 3Þ by the method were 0.1–8 fg for FR, Bbf and BgPe; 0.5–4 fg for Py, BaA, Chr, BaP, IDP and BkF. Blank samples were routinely analyzed to evaluate analytical bias and precision. Blank levels of individual PAHs were normally very low and in most cases not detectable. In addition, recoveries of PAHs were determined by adding a known PAH standard amount in a blank filter. The average recoveries of 9 PAHs varied from 90% to 110%. 2.4. Back trajectory analysis The source of the air samples was predicted with the online program, Meteorological Data Explorer (METEX, http://cgermetex.nies.go.jp/metex/), which was developed by the National Institute for Environmental Studies (NIES), Japan. Meteorological data was obtained from the European Centre for Medium-range Weather Forecasting (ECMWF). The system calculates three-dimensional air mass trajectories (height, longitude and latitude) with a time resolution of 6 h and horizontal resolution 2.51  2.51 and vertical resolution was 15 equal levels from surface pressure to 10 hPa. 2.5. Principal component analysis (PCA) PCA is a multivariate statistical method that is frequently used in environmental science to reduce the dimensionality of a data set (Mai et al., 2003; Terzi and Samara, 2005; Dahle et al., 2003). It transforms the original variables, which may possess

a significant correlation, into a set of uncorrelated orthogonal variables, called principal components (PCs) (Gambaro et al., 2004). The number of PCs used to interpret the results is determined by a scree test (Cattell, 1966). The first PC is oriented to explain as much variation in the data as possible. The second PC is orthogonal to the first, and explains the next largest variation in the data, and so forth. Often the first two or three PCs account for a large proportion of the variance. The relationship between samples can be presented graphically as a score plot of the PCs. Objects that are close to each other in the score plot are similar and vice versa. In our study PCA was used to analyze the different compositions of the PAHs in each sampling period or sampling site. For the PCA, the concentration ratios of FR, Pyr, BaA, Chr, BbF, BkF, BaP, BgPe and IDP to the total PAHs were used as the multiple dimensions. PAH measurements for Shenyang and Kanazawa in winter were obtained from our previous report (Tang et al., 2005b). PCA was carried out with STATISTICA ver. 6.0 (StatSoft, Tulsa, OK, USA). 3. Results and discussion 3.1. Weekly variations of PAHs and airborne particulate matter The changes of atmospheric concentrations of PAH groups (4-, 5- and 6-ring PAHs) and airborne particulate matter (PM) at Wajima are shown in Fig. 2. The concentration of PM at Wajima was relatively high from 11 March 2005 to 6 May 2005. During this period, Asian Dust transported from the Asian Continent was detected at Wajima about four times (Japan Meteorological Agency http:// www.jma.go.jp/jp/kosa/index.html). However, the times of occurrence of Asian Dust were not correlated with higher PAH concentrations, suggesting that the contribution of the Asian Dust to the transportation of PAHs was insignificant. Guo et al. (2003) also found no correlation between PM and PAH concentrations in Qingdao, China. On the other hand, all of the PAH groups (4-, 5- and 6-ring PAHs) at Wajima tended to increase during the period from 15 October 2004 to 19 November 2004. The concentrations remained high until 18 March 2005 and then decreased. Cities in North of China, central heating systems are widely used to deliver hot steam for residents in winter. The main energy source of this kind of

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Fig. 2. Weekly variations of PAHs and PM at Wajima during the sampling period. Dates indicate the first day of a 7 day sampling period.

heating system is coal. The system supplies hot steam to 200 million urban residents across 14 provinces, municipalities and autonomous regions. It is not easy to estimate the effect of the central heating systems on the environment, but the high concentration of SO2 during the heating period in Beijing (He et al., 2001) suggests that the burden must become much heavier. These central heating systems are operated by the local governments. During our study period, they provided heat from 15 November 2004 to 15 March 2005 for all of northern China. However, in the colder parts, heating was provided from 15 October 2004 to 15 April 2005. For example, in Shenyang, the capital of Liaoning province, it begins on 1 November and ends on 31 March next year, and in Beijing it runs from 15 November to 15 March next year. In some northern cities, hospitals and hotels, the heating season lasts from about 1 November to 1 April. The period of high atmospheric concentrations of PAHs at Wajima approximately coincided with the heating period of China described above. Large parts of 3- and 4-ring PAHs, which have relatively high vapor pressures, are distributed in the gas phase at ambient temperature (Tang et al., 2005a). On the other hand, most of the 5- and 6-ring PAHs are mainly in the particulate phase, regardless of the charge in the ambient temperature (Tang et al., 2005a;

So¨derstro¨m et al., 2005; Tsapakis and Stephanou, 2005; Yamasaki et al., 1982). The concentrations of 5and 6-ring PAHs remained at higher levels during the heating period of China (Fig. 2). 3.2. Meteorology The typical atmospheric pressure pattern of Northeast Asia in winter is characterized by a high-pressure area in the west and a low-pressure area in the east. This results in the long-range transport of air masses from the Asian Continent to Japan (Terada et al., 2002). Several pollutants such as SO2 have been shown to be transported from the Asian Continent to Japan in this way (Uno et al., 1997). However, in summer, air masses cannot be easily transported from the Asian Continent to Japan because of a different pressure distribution. Weather charts of 1 February 2005 and 1 August 2005, downloaded from the website of the Japan Meteorological Agency (http://www.data.kishou. go.jp/yohou/kaisetu/hibiten/index.html), are shown in Fig. 3a and b as typical pressure distribution examples of winter and summer, respectively. The transport of pollutants is often analyzed by back trajectory analysis (Kato et al., 2004; Lee et al., 1998; Osada et al., 2003). We used this method to analyze the data in Fig. 2 in order to find

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Fig. 3. Typical weather charts of (a) winter (1 February 2005) and (b) summer (1 August 2005).

the origins of the PAHs observed at Wajima, Japan. In the free troposphere layer, from 1 to 2 km above the ground, pollutants are easily transported by the wind because they are free from the influence of the friction of the ground. In this layer, air masses would be transported from Northeast China to Japan by the northwest wind in only 3 days. Thus, by this method we calculated the 72 h back trajectories at 1500 m above ground level of the air samples of Wajima. Trajectories were calculated every day during the whole sampling period (from 15 September 2004 to 14 September 2005) and all of them are shown in Fig. 4. Most of the back trajectories of the samples from 15 October 2004 to 15 April 2005, which corresponds to the heating period of China, passed through Northeast China, which has a high density of population and industry (Fig. 4b–h). On the other hand, most of the trajectories during the no-heating period did not pass through the Asian Continent (Fig. 4a, i–l). These results suggest that the atmospheric PAHs at Wajima were probably affected by combustion particulates transported from the Asian Continent during the heating period of China. 3.3. Comparison of PAH concentrations between Wajima, Shenyang and Kanazawa We wished to know whether the atmospheric PAHs at Wajima were more similar to those of a large city in Northeast China in which the main emission source of PAHs is coal or a large Japanese city in which the main emission source of PAHs is

diesel-engine vehicles. As the two cities that fit these descriptions, Shenyang (population 7 million, 1250 km from Wajima) and Kanazawa (population 450,000, 100 km from Wajima) are selectable (Tang et al., 2005b). At Wajima, the concentrations of all of the PAHs were higher during the heating period of China than during the no-heating period (Table 1). The total PAH concentration was about four times higher during the heating period. However, the PAH levels at Wajima were much lower than those at Shenyang (Kanazawa) by the factors of 74 times for BgPe, 1300 times for BaA (3.2 times FR and 2 times for BaA during the heating period of China. The total concentration of the eight PAHs at Wajima (0.52 ng m3), during the heating period, was about nine times lower than those in Kanazawa (4.58 ng m3) and about 430 times lower than in Shenyang (226 ng m3). Even though the levels at Wajima were much lower than those at Shenyang, FR and Pyr were predominant not only at Wajima during the heating period of China (15 October 2004–15 April 2005) but also at Shenyang. Because those large parts of 4-ring PAHs are distributed in the gas phase as described above, atmospheric concentrations might be much higher than those in Table 1. That tendency was not observed in the case of Kanazawa. 3.4. Principal component analysis PCA was applied to PAH profile data of Wajima (Fig. 1) and corresponding data of Shenyang

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(winter) and Kanazawa (winter). After varimax rotation for a clearer resolution of components, the first two PCs were found to explain 56.93% of the variance in the original data set. And a score plot obtained from those first two PCs visualizes the differences in the profile of PAHs (Fig. 5). Samples

were divided into two groups by PC1 (35.14%). On the left-hand side of the score plot samples of Wajima (heating period) and Shenyang (winter) were predominantly found, whereas samples of Wajima (other period) and Kanazawa (winter) were found almost on the right-hand side of the score

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Table 1 Concentrations of PAHs at Wajima, Shenyang and Kanazawaa Compound

Wajima

Shenyangb 2001/1/14–2001/1/21 (n ¼ 3)

Kanazawab 1998/12/31–1999/2/1 (n ¼ 6)

Heating period 2004/10/15–2005/4/15 (n ¼ 27)

No-heating period 2004/9/17–2004/10/ 8+2005/4/22–2005/9/9 (n ¼ 23)

4-ring FR Pyr BaA Chr

0.1470.07 0.1070.05 0.0270.01 0.0570.02

0.0370.04 0.0270.02 0.0170.01 0.0170.01

51.6718.0 51.0714.5 25.277.1 32.4711.0

0.4570.14 0.4470.15 0.4170.16 0.6370.19

5-ring BbF BkF BaP

0.0770.03 0.0370.01 0.0370.01

0.0270.01 0.0170.01 0.0170.01

19.976.3 9.672.6 19.674.9

0.6970.21 0.2970.09 0.4270.18

6-ring BgPe IDP

0.0570.02 0.0470.01

0.0270.01 0.0170.01

3.671.3 13.174.4

0.8370.27 0.4470.13

Total PAHs

0.5270.23

0.1270.11

226.0769.2

4.5871.52

a

All concentrations in ng m3. All data represent mean7SD. Values cited from Tang et al. (2005b).

b

Fig. 5. Score plot of the first two PCs on PAH profiles of Wajima in heating period (B) and non-heating period (J), in Shenyang in winter (&) and in Kanazawa in winter (n). Values of Kanazawa and Shenyang are cited from Tang et al. (2005b).

plot. This suggested that the composition of PAHs at Wajima during the heating period was similar to that at Shenyang in winter.

We previously showed that the main contributors to atmospheric PAHs and NPAHs in Japanese cities were automobiles, especially diesel-engine vehicles,

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while they were coal combustion systems in Chinese cities (Tang et al., 2005b). And the PAHs’ compositions of these two emission sources are quite different (Tang et al., 2002, 2005a, b; Kakimoto et al., 2000, 2002; Hattori et al., 2007). Because no emission sources are near the sampling station at Wajima, we conclude that the atmospheric PAHs at Wajima were strongly influenced by combustion particulates transported from the Asian Continent during the heating period of China. On the other hand, some of the samples collected during the heating period at Wajima appeared on the right side of the plot (Fig. 5). We investigated the PAHs’ compositions of those samples and a high percentage of BgPe (0.10–0.14) was found, which is higher than it was for other samples (0.5–0.13) during the heating period (n ¼ 8, po0.001). Particulate organic samples collected in tunnels were found to be enriched in BgPe, which is a characteristic of particulates in gasoline engine exhaust (Miguel et al., 1998). In winter, the BgPe/ total PAH ratio in Kanazawa (0.83/4.58 ¼ 0.181) was an order of magnitude higher than the ratio in Shenyang (3.6/226 ¼ 0.016) (Table 1). This suggests that Japanese domestic PAHs contributed a little to the PAHs at Wajima even during winter. 4. Conclusions Higher atmospheric PAH concentrations were observed at Wajima during the heating period of China. A principal component analysis showed that the composition of nine PAHs at Wajima, during the heating period of China, was close to that at Shenyang but not to that of Kanazawa. Meteorological analysis indicated that the air was transported from Northeast China over the Japan Sea in winter. These results strongly suggest that PAHs emitted in China, during the heating period, were transported over long distances to Japan. Acknowledgments This research was a part of the international project of the 21st century COE program ‘‘Environmental monitoring and prediction of long- and short-term dynamics of Pan-Japan Sea’’, supported by a Grant in Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan. This research was also a Joint Project supported by JSPS-NSFC Japan–China Scientific Cooperation Program.

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