Atmospheric Research

Transcription

1 Atmospheric Research 99 (2011) Contents lists available at ScienceDirect Atmospheric Research journal homepage: Characteristics of the ambient particulate PAHs at Seoul, a mega city of Northeast Asia in comparison with the characteristics of a background site Ji Yi Lee a,1, Yong Pyo Kim a,,1, Chang-Hee Kang b,2 a Department of Environmental Science and Engineering, Ewha Womans University, 11-1 Daehyun-dong, Seodaemun-gu, Seoul, , Republic of Korea b Department of Chemistry, Cheju National University, 1 Aradong, Jeju , Republic of Korea article info abstract Article history: Received 29 January 2010 Received in revised form 13 July 2010 Accepted 30 August 2010 Keywords: Particulate PAHs TSP Northeast Asia Atmosphere To identify the ambient characteristics of a mega city in Northeast Asia, the particulate PAHs in TSP were measured for 18 months at Seoul, the capital of Korea. The average concentration of the ambient particulate PAHs at Seoul for the sampling period was 26.6±28.4 ng m 3 with the range from 1.57 to 166 ng m 3. It showed winter maxima and summer minimum mainly due to the increased fuel consumption in winter both at Seoul and Northeast Asia. The ambient level of PAHs in Seoul was lower than the cities in China but higher than other urban areas. The stronger relationship between the ambient particulate PAHs concentrations and the inverse of the ambient temperature (1/T) at Seoul compared to Gosan, a background site in Korea and the difference of the distributions of BeP/BaP ratios at Seoul and Gosan might be due to the characteristics of Seoul which was governed by both transport from outside and local emissions. The relationship between the particulate PAHs concentration and (1/T) can be used as an indicator for those two factors for Seoul Elsevier B.V. All rights reserved. 1. Introduction Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous organic pollutants mainly produced by incomplete combustion processes such as biomass burning, oil combustion, coal combustion and wood combustion (ATSDR, 1995). Some of PAHs which mainly exist in the particle phase in the atmosphere are reported to be probable human carcinogens (ATSDR, 1995). Moreover, PAHs derivatives such as nitro-pahs are more toxic than parent PAHs (Marr et al., 2006). Thus, PAHs are designated as one of the considered Persistent Toxic Substances (PTS) in Central and Northeast Asia (Region VII) under the Stockholm convention (UNEP, 2002). Recently, heterogeneous reactions of particulate PAHs have been studied as surrogates for heterogeneous chemistry of several types of Corresponding author. Tel.: ; fax: addresses: yijiyi76@ewha.ac.kr (J.Y. Lee), yong@ewha.ac.kr (Y.P. Kim), changhee@cheju.ac.kr (C.-H. Kang). 1 Tel.: Tel.: organics since such reactions could change the particle hygroscopicity in cloud processing (Jones et al., 2004; Esteve et al., 2006; Marr et al., 2006). Because the Northeast Asia region is the world's largest fossil fuel consumption region (BP, 2007), it has been speculated that emissions and impacts of PAHs would be large. Thus, in order to estimate adverse human health and climate change effects of ambient PAHs, quantifying the ambient level of PAHs and understanding their characteristics at urban areas in Northeast Asia should be required. Recently, several studies on the PAHs levels in the urban areas in Northeast Asia, especially in China, have been reported (Tang et al., 2005; Liu et al., 2007a,b). The average PAHs concentrations in fall and winter at several cities in north and north-west China were the highest globally. Also, it was found that there was no significant difference in the ambient PAH concentrations between the urban and rural areas in China mainly because of the predominant sources being biomass and domestic coal combustion (Tang et al., 2005; Liu et al., 2007a,b). It was identified that the transport of ambient trace species (Park et al., 2004), especially, PAHs (Lee et al., 2006) from China to the downwind area such as Korea and Japan be /$ see front matter 2010 Elsevier B.V. All rights reserved. doi: /j.atmosres

2 J.Y. Lee et al. / Atmospheric Research 99 (2011) significant. Lee et al. (2006) observed the temporal trend of the particulate PAHs level at Gosan, a background site in Korea and conclude that the influence of long range transport of particulate PAHs from China was dominant at Gosan. However, it is not clear how the PAHs levels in China be related with the levels in other countries in the region including the mega cities since long range transport of primary and secondary aerosols are thought to be significant in the region. Seoul is the capital of the Republic of Korea and one of mega cities in Northeast Asia with 10 million inhabitants and 2.5 million vehicles. However, only a few ambient PAHs measurement studies have been reported for Seoul (Bae et al., 2002; Lee et al., 2008; Park et al., 2002; Panther et al., 1999). Park et al. (2002) observed the seasonal variation of the gas and particle phase PAHs levels in five intensive sampling periods from October 1998 to December They found that seasonal trend in atmospheric PAH concentrations in Seoul was highly influenced by the fossil fuel usage for domestic heating, boundary layer height, and air temperature. Panther et al. (1999) had measured particulate PAHs in Seoul from March to December, 1993 on a 6 day cycle using a TSP high volume air sampler. They found that PAH concentrations were higher during winter mainly due to the use of fossil fuels for heating in winter and other multiple processes such as decreased photolytic degradation in winter, transport of pollutants from other sources. Bae et al. (2002) measured ambient particle size distributions and dry deposition fluxed at several areas in Korea on winter and spring, Lee et al. (2008) measured the particulate PAHs size distributions with the particle size up to PM10 at Seoul in June and December, However, these measurements were rather episodic or short term and, thus could not identify temporal trend. Lee and Kim (2007) suggested that the effect of long range transport could be identified even in Seoul addition to the effect of local emission. Thus, it is essential to identify major characteristics of mega cites in Northeast Asia. It is often more informative to compare the result in urban area with that in background area in Northeast Asia to understand the transport characteristics. In this study, (1) a long-term temporal variation of the atmospheric particulate PAHs levels at Seoul, a mega city in Northeast Asia is quantified, (2) the concentration at Seoul is compared with the levels in other urban areas in Northeast Asia and the world, (3) the emission and transport characteristics of particulate PAHs observed at Seoul are discussed by comparing with the characteristics at a background area in Northeast Asia, Gosan, and, finally (4) the major factors that cause these differences between Seoul and Gosan are discussed in relation with the meteorological conditions. 2. Experiment Samples were collected on a 3 m high platform on the roof of Asan Hall in Ewha Womans University, a five-storey building of 15 m height. It is adjacent to a road in west, Mt. Ansan in north, and stands on a hill commanding the campus. Sampling at Seoul was carried out for 24 h at every sixth day with no rain from August 2002 to December Total of 68 samples were obtained. The sampling procedures used in this study were conformed to the methods of TO-13A (US EPA, 1999). Detailed descriptions on the sampling and analytical procedures were given elsewhere (Lee et al., 2006). In brief, a high volume TSP sampler (Tisch Environmental, TE-1000) was operated at a calibrated flow rate of m 3 min 1 to obtain the total sample volume of greater than 300 m 3 over the 24 h period. Particles were collected on the pre-baked (at 400 C for 5 h) quartz fiber filters (QFFs, Whatman, QM-A, cm diameter). Particulate PAHs samples collected on the QFFs were extracted for 30 min in an ultrasonic bath with dichloromethane solvent 25 ml and then mechanically shaken for 5 min with a vortex mixer. The extracts were filtrated through a 0.45 μm pore size syringe filter. The above extraction procedure has been repeated three times for the residual sample filters. These extracts were transferred to a vessel and concentrated at 20 C to a volume of 1 ml using an evaporator (Zymark, Turbovap 500). Then phenanthrene-d 10 was added to each concentrated sample solution as an internal standard for analysis. Seventeen PAHs compounds were identified and quantified using a Hewlett Packard 5890 gas chromatograph equipped with a 5972 mass selective detector. The names of the analyzed PAH compounds and their abbreviations are given in Table 1. The QFFs field blanks were prepared and analyzed for each set of field samples with the same procedure. Extraction recoveries were determined by spiking the PAHs standard solution (Aldrich, B for BeP and Supelco EPA 610 Polynuclear Aromatic Hydrocarbons Mixture for others) in the pre-extracted QFFs (real filter samples in which PAHs were extracted). The mean extraction recoveries for particulate PAHs ranged from 80 to 94% (Table 1) and these recoveries were accounted for in the concentration calculation. The accuracy of the analytical procedure was tested through the analysis of National Institute of Standards and Technology (NIST, USA) standard reference materials (SRM) 1649 urban dust sample. The extraction recoveries and analytical accuracy results for the SRM 1649 samples are also presented in Table 1. Among the 17 PAH compounds identified, Nap, Ace, Acy, and Flu exist predominantly in the gas phase in the normal atmospheric conditions. Because the major focus of this study is on the particulate PAHs concentration, these compounds were excluded for further data analysis. 3. Results and discussion 3.1. The level of the particulate PAHs concentrations at Seoul The average concentration of the ambient particulate PAHs at Seoul between August 2002 and December 2003 was 26.6± 28.4 ng m 3 with the range between 1.57 and 166 ng m 3.It showed winter maxima and a summer minimum as shown in Fig. 1. The particulate PAHs concentrations in several urban areas are arranged in Table 2 for comparison. The average concentrations of total PAHs in this study were comparable to the measurement result at Seoul from 1998 to 1999 (Park et al., 2002) but higher than the result in 1993 (Panther et al., 1999) indicating that the particulate PAHs concentrations at Seoul have not decreased during the last 10 years. Generally, the levels of the ambient particulate PAHs at the urban areas globally were in the order of 10 ng m 3 except

3 52 J.Y. Lee et al. / Atmospheric Research 99 (2011) Table 1 Particulate PAHs extraction recovery and analysis results of the NIST SRM-1649 urban dust samples. PAH compounds Abbrev. Recovery (%) Certified value (μg kg 1 ) Measured value (μg kg 1 ) Naphthalene Naph 91 Acenaphtylene Acy 84 Acenaphthene Ace 84 Fluorene Flu 91 Phenanthrene Phen ± ±0.49 Antracene Anthr ± ±0.06 Fluoranthene Flt ± ±0.18 Pyrene Pyr ± ±0.22 Benz(a)anthracene BaA ± ±0.59 Chrysene Chry ± ±0.54 Benzo(b)fluoranthene BbF ± ±0.40 Benzo(k)fluoranthene BkF ± ±0.29 Benzo(e)pyrene BeP 84 Benzo(a)pyrene BaP ± ±0.82 Indeno(1,2,3-cd)pyrene Ind ± ±0.66 Dibenz(a,h)anthracene DahA ± ±0.04 Benzo(g,h,i)perylene BghiP ± ±0.69 Beijing. The level of the ambient particulate PAHs at Beijing was about one order magnitude higher than other urban areas. It might be due to the high consumption of fossil fuels, especially, coal in this area (Zheng et al., 2005). The particulate PAHs concentrations at Seoul were higher than Tokyo (Kumata et al., 2000). Comparing to the urban areas in China, the particulate PAHs concentrations at Seoul were lower than that at Beijing (Kumata et al., 2000; Okuda et al., 2006), Gaungzhou (Tan et al., 2006), and Hong Kong (Guo et al., 2003). Also, the level of PAHs concentration at urban areas in Taiwan (Fang et al., 2004) was higher than that at Seoul. In the global distribution, the particulate PAHs concentration at Seoul was generally higher than those at Birmingham in UK (Smith and Harrison, 1996), São Paulo in Brazil (Vasconcellos et al., 2003), Melbourne in Australia (Panther et al., 1999) Algiers in Algeria (Yassaa et al., 2001), but except at Thessaloniki in Greece (Manoli et al., 2002). The particulate PAHs concentrations in this study are similar to that at Chicago in USA (Simcik et al., 1997) because the particulate PAHs concentration at Chicago was the sum of 19 individual PAH compounds. In the chemical mass balance model (CMB) study for the measurement data reported in this work, Lee and Kim (2007) reported that, on the average, gasoline and diesel vehicles were the major emission sources of the measured PAHs at Seoul. However, the high contributions of biomass burning and coal combustions were also estimated in fall and winter. They argued that the majority of the biomass and coal combustion related PAHs were from China and/or North Korea since these sources were not strong in and around Seoul. Thus, it is possible that the generally lower PAHs concentration at Seoul than the urban areas in China but higher value than Tokyo might be caused by the distance of transport from China to Korea and Japan in addition to the local emissions of PAHs in Korea. To further study this point, it is essential to compare the Seoul data with the data at a background area in Northeast Asia Temporal trend of PAH compounds Fig. 1. Temporal trends of the particulate PAHs concentration (line) and BeP-to-BaP ratio (dot symbol) measured at (a) Seoul and (b) Gosan. Sampling periods were from August 2002 to December 2003 at Seoul and from January 2002 to January 2004 at Gosan, respectively. As Gosan site is one of representative background site in Northeast Asia, several intensive and routine measurement studies including Pacific Exploratory Mission (PEM) West A and B, Aerosol Characterization Experiment (ACE) Asia, and Atmospheric Brown Cloud (ABC) have been performed at this site in order to understand the characteristics of long range transport of air pollutants in Northeast Asia region (Lee et al., 2006). Here, to understand the temporal trend and characteristics of particulate

4 J.Y. Lee et al. / Atmospheric Research 99 (2011) Table 2 Comparison of the particulate PAHs concentrations (ng m 3 ) in this study with the results measured at urban areas in worldwide. Continent Country Region Sampling period Particle size Average PAHs concentration a Number of samples Reference Asia South Korea Seoul Aug 2002 Dec 2003 TSP This study Seoul Oct Nov 1998, Feb Mar, TSP 25.6 Park et al. (2002) May Jun, Sep, Nov Dec 1999 Seoul Mar Dec 1993 TSP Panther et al. (1999) Japan Tokyo Nov Dec 1998 TSP 18.7 b 3 Kumata et al. (2000) China Beijing Oct Apr 2005 PM Okuda et al. (2006) China Beijing Jul and Dec 1998 TSP 163 b 4 Kumata et al. (2000) China Guangzhou Jun 2002 Jun 2003 PM Tan et al. (2006) China Hong Kong Jun Dec 1993 TSP Panther et al. (1999) China Hong Kong Jun Aug 2001 PM ( ) c 4 Guo et al. (2003) Nov 2000 Mar 2001 PM ( ) 7 Guo et al. (2003) Taiwan Taichung Aug 2002 Jul 2003 TSP Fang et al. (2004) Thailand Bangkok Apr Oct 1993, Feb Apr 1994 TSP Panther et al. (1999) Pakistan Lahore Aug Sep 1992 TSP 80.3 Smith et al. (1996) Indonesia Jakarta Dec 1992 Dec 1993 TSP Panther et al. (1999) America USA Chicago May and Jul 1994, Jan 1995 TSP 45.4 d ( ) 30 Simcik et al. (1997) Brazil São Paulo Aug Sep 2000 TSP 3.1 e 22 Vasconcellos et al. (2003) Europe U.K. Birmingham Winter TSP 17.1 Smith and Harrison (1996) Summer TSP 3.6 Smith and Harrison (1996) Greece Thessaloniki Jun 1994 May 1995 PM Manoli et al. (2002) Oceania Australia Melbourne Jan Dec 1993 TSP Panther et al. (1999) Africa Algeria Algiers May Sep 1998 TSP 8.3 f ( ) 14 Yassaa et al. (2001) a Based on sum of 12 PAH compounds (Phen, Antr, Flt, Pyr, BaA, Chry, BbF, BkF, BaP, Ind, DahA, BghiP) concentration. b 11 compounds (DahA was not reported). The Chry and BkF concentration were expressed as (Chry+triphenylene) concentration and B(k+j)F concentration due to co-elution. c Indicate the range of concentration. d Total concentrations of 19 PAH compounds were reported. e 11 compounds (BkF was not reported). f 10 compounds (Phen and Anthr were not reported). PAHs concentration at Seoul, we tried to compare the Seoul data with the measurement data of particulate PAHs at Gosan by Lee et al. (2006). The temporal trend of the total PAH concentrations at Seoul and Gosan are shown in Fig. 1. The concentrations of particulate PAHs were high from November to March, with the peaks in January at both sites. The average PAHs concentration during summer (from June to August) was the lowest mainly due to frequent rain, high ambient temperature, and small amounts of fossil fuel usage and clear air from the Pacific. This seasonal pattern was generally observed from several urban and remote areas (Park et al., 2002; Guo et al., 2003; Fang et al., 2004; Lee et al., 2006). The high concentrations of particulate PAHs during winter are caused due to the increased fossil fuel usage for heating and transport of PAHs from outside, preferential particle phase partitioning of PAHs, and the decreased photo-oxidation of PAHs (Lee et al., 2006). At Gosan, the average concentration of total particulate PAHs was 3.65±4.74 ng m 3 with the range from 0.06 to 20.9 ng m 3 (Lee et al., 2006). The level of particulate PAHs concentration at Seoul was about one order higher than that in Gosan based on the unit of air volume. The average annual PM10 (particulate matter with the aerodynamic diameter less than or equal to 10 μm) concentrations at Seoul and Gosan (measured by National Institute of Environmental Research in Korea) were 70.8 and 19.9 μgm 3 during the sampling period. For being sure the comparison of particulate PAHs concentration between Seoul and Gosan, the annual PM10 concentration was applied to the particulate PAHs concentration and approximate values of particulate PAHs concentration in ng μg 1 of PM10 at Seoul was 0.38 ng μg 1 which is about four times higher compared to the PAHs concentration of Gosan (0.09 ng μg 1 of PM10). The level of particulate PAHs concentration at Gosan was generally one or two order higher levels compared with those in several background and/or remote areas although the Gosan site has the geographic characteristics of a background area. Lee et al. (2006) reported the high concentrations of particulate PAHs at Gosan was mainly due to the transport of PAHs emitted from China, especially, in winter. Fig. 1 also shows the temporal trend of the BeP/BaP ratios at Seoul and Gosan, respectively. Since ozonolysis and photo degradation of BaP are faster than BeP (Katz et al., 1979). The BeP/BaP ratio contains information on the relative residence time of the PAHs in the atmosphere (Kleeman et al., 1999; Lee et al., 2006). For example, half-life of BeP under the simulated atmospheric condition was one order higher than that of BaP (Katz et al., 1979). Also, since the ratio depends on emission sources (e.g from gasoline vehicle, from diesel exhaust, from coal combustion, and 0.44 from biomass burning) (Simcik et al., 1997), the measured ratio values can indicate probable emission sources. As shown in Fig. 1, the degree of the temporal variation of BeP/BaP ratios at Seoul was smaller (ranged from 0.6 to 1.2 except the results of three sampling days) than at Gosan (ranged from 0.02 to 2.36). The lowest ratios of BeP/BaP ( ) at Gosan were observed during three sampling days of the warm season due to the low concentration of BeP. Note that though low, the concentrations of BeP were above the method detection limit (MDL) of BeP (2.6 pg m 3 ). The higher ratios of

5 54 J.Y. Lee et al. / Atmospheric Research 99 (2011) BeP/BaP in the cold season with higher PAHs concentrations than the warm season were due to the effect of the longer residence time from the sources caused by the differences in air parcel trajectories at Gosan (Lee et al., 2006). The lower variation and lower values of BeP/BaP ratios at Seoul than Gosan were due to more fresh PAHs at Seoul. Though the PAHs levels at Seoul is affected by transport from outside, still the PAHs concentrations at Seoul were more affected by the emissions from local sources than Gosan. Thus, the BeP/BaP ratios might be consistently lower in all seasons than Gosan. On the contrary, the high BeP/BaP ratio values observed at Gosan indicate that the PAHs were aged one. Also, the large variation of the BeP/BaP ratios at Gosan indicates the distributions of PAHs concentrations were very sensitive for the atmospheric conditions at Gosan such as air parcel trajectories. The higher ratio of BeP/BaP during warm season at Seoul is easily explained by the difference of photochemical activities. At Gosan, however, the longer residencetime thanatseoul mightbemoreinfluential than the difference of photochemical activities, and, thus showed a higher ratio of BeP/BaP during the cold season. Lee et al. (2008) measured the particulate PAHs size distributions and applied the BeP/BaP ratio analysis for the PAHs composition in fine mode particles (in the size ranges of and μm diameter in June and December, respectively) to find a clue to the probable emission sources. They found that the ratio values in summer (~2) suggested vehicular emissions while in winter the ratio values (~1) suggested coal related emissions and firewood fire emissions Correlation of the PAHs level with the meteorological conditions The distribution of semivolatile organic compounds (SVOCs) such as PAH compounds between the gas and particle phase depends upon the ambient temperature and the characteristics of atmospheric particulate matter (PM) (Pankow, 1991). K P ðm 3 μg 1 Þ = F = TSP A log K P ðm 3 μg 1 Þ = m r T + b r ð2þ where, K p is partitioning coefficient of PAH compounds (m 3 μg 1 ), A and F are the gas and particle phase concentrations of PAH compounds (ng m 3 ), TSP is total PM concentration (μgm 3 ), and T is ambient temperature (K). Generally, when ambient temperature is low and PM concentration is high, transfer of gaseous PAHs to particles is favored. If the concentrations and composition of PM are constant, the degree of gas-to-particle partitioning of PAHs can be expressed as linear function of the inverse of ambient temperature (1/T) as expressed in Eq. (2). In this study, because only the particulate PAHs concentration was measured, the effect of temperature to gas-to-particle partitioning of PAH compounds was estimated by plotting the relationship between the particulate PAH concentration and (1/T). Fig. 2 shows the correlation values (r 2 ) of (1/T) and the concentrations of individual PAH compounds in log scale for ð1þ Fig. 2. Correlations values (r 2 ) of the concentrations in log scale for individual PAH compounds (log [PAH concentration]) with the inverse ambient temperature (1/T) at Seoul and Gosan (the lower molecular weight (MW) species Phen, Flt, and Pyr (MW: ) and the higher MW species BeP, Ind, and BghiP (MW: )). individual PAH compounds (log [PAH concentration]) at Seoul and Gosan. In Fig. 2, Phen, Flt, and Pyr are defined as the lower molecular weight (MW) species (MW: 178~202) and the higher MW species include BeP, Ind, and BghiP (MW: 252~276). When PAHs are emitted, lower MW PAHs compounds tend to distribute to the gas phase due to the higher vapor pressure in the atmosphere, especially, in warm season. On the contrary, higher MW PAH compounds which have lower vapor pressure in the atmosphere exist mainly in the particle phase irrespective of season. At Seoul, log [PAH concentration] for lower MW PAH compounds showed good relationship with (1/T) as shown in Fig. 2. However, the correlations of log [PAH concentration] with (1/T) for higher MW PAH compounds were low. It means the phase partitioning of lower MW PAH compound in the atmosphere of Seoul depends on the ambient temperature. Thus, the gas-to-particle partitioning of these compounds should be one of the major factors determining the temporal distribution of particulate and gaseous PAHs concentrations in the atmosphere of Seoul. However, at Gosan, the correlations between log [PAH concentration] and (1/T) are irrelevant to the MW of PAH compounds (Fig. 2). This result is different from Seoul and it indicates temperature dependence of the PAHs concentrations in the atmosphere of Gosan is low compared to Seoul. Although the concentrations and characteristics of TSP and gas phase PAHs are different in both sites, the difference of the temperature dependence of the particulate PAH concentrations between Seoul and Gosan might originate from the characteristic of the sites. Wania et al. (1998) explained the temperature dependence of the atmospheric concentrations of SVOCs based on the dynamic approach including the kinetics of air surface exchange. They reported that the temperature dependence of the atmospheric concentration of SVOCs, especially polychlorinated biphenyls (PCBs) is good when the fugacity (partial pressure) in soil surface is high compared to the fugacity in inflowing air. Because PAHs is one of major SVOCs as like PCBs, the tendency of PAHs by the temperature in the atmosphere might be similar to PCBs. Freshly emitted PAHs from local

6 J.Y. Lee et al. / Atmospheric Research 99 (2011) sources can be expressed as high fugacity in soil surface and then the transported PAHs from outside of Seoul can be expressed as lower fugacity as in the study of Wania et al. (1998). Thus, the clear temperature dependence of particulate PAH compounds shown in Seoul might be related to the result of Wania et al. (1998) which has shown high temperature dependence of the atmospheric concentration of SVOCs when the fugacity in soil surface was an important factor. On the other hand, Gosan is a representative background area and, thus, the long range transport of PAHs from outside of Gosan is more important than the emission of PAHs from the local sources around Gosan. Namely, the situation in Gosan can be interpreted as an area of low surface concentration where atmospheric levels are dominated by the inflow of air. Another possible explanation for low temperature dependence of PAHs concentrations in Gosan is the small variation of temperature in Gosan compared to Seoul. However, because the annual temperature range (0.5 to 26.0 C) in Gosan was similar to that temperature range of Seoul which ranged from 6.5 to 27.7 C in Seoul, the small variation of temperature in Gosan should not be the major factor for the low temperature dependence of PAHs concentrations. Liu et al. (2007b) measured total (gas+particle phase) PAHs in the air of 37 cities and 3 rural locations across China during the winter, spring, summer, and fall of 2005, using PUF disks as passive air samplers. They found that PAHs concentrations in the cities of China were the highest in the world and a significant correlation between the average annual concentrations of total PAHs in the cities and the inverse of annual average ambient temperature were shown. Because of the different unit of the PAHs concentration in the results of Liu et al. (2007b) from this study, we could not directly compare the slope value between the PAHs concentration and (1/T) in the cities of China, Seoul, and Gosan. However, strong correlation between PAHs concentration and (1/T) in the cities of China is consistent with the expectation. This result might be related to strong local emission of the PAHs concentrations in the cities of China. While the PAHs concentration in Seoul might be influenced by transport of PAHs from outside in addition to the local emissions and Gosan would be mostly affected by transport from outside. Thus, compared to the cities of China, the correlation of PAHs concentration with the ambient temperature in Seoul might be less significant. Evidently, other factors might affect the relationship such as wind speed (Wania et al., 1998) and the differences in the sorption mechanisms (Goss and Schwarzenbach, 1998). Therefore, further studies are warranted to fully understand the physical chemical processes that govern the relationship between the ambient PAHs levels and (1/T). One example is the seasonal measurement of both gas and particle phase PAHs concentrations. 4. Summary It becomes imperative to quantify the levels of ambient air pollutants in the mega cities in Northeast Asia and to understand themajorfactorsthataffecttheambientlevels.thoughseoulisa mega city, the ambient PAHs measurement data have been scarce. The temporal variation of the atmospheric particulate PAHs levels at Seoul, a representative urban area in Korea, was measured for 18 months from August 2002 to December 2003 to fulfill those objectives. The average concentration of the ambient particulate PAHs at Seoul for the sampling period was 26.6±28.4 ng m 3 with the range from 1.57 to 166 ng m 3. It showed typical seasonal distribution of particulate PAHs which is winter maxima and a summer minimum mainly due to the increased fuel consumption in winter both at Seoul and Northeast Asia. Compared to the ambient levels of PAHs in Seoul to other urban areas, those in Seoul were lower than the cities in China but higher than other urban areas such as Tokyo. The PAHs concentration in Seoul is compared with that in Gosan, a representative background site in Korea to further understand the characteristics of a mega city in Northeast Asia in which both local emissions and transport from outside are important. Based on the absolute levels and the temporal trend of the PAHs concentration and BeP/BaP ratio analysis for both sites, it is concluded that the PAHs level in Seoul is more influenced by local emissions than Gosan. From the difference of the variation of BeP/BaP ratios and the temperature dependency of the PAHs concentrations in the atmosphere of Seoul and Gosan, we could evaluate the influence of long range transport vs. local emission. The result of Liu et al. (2007b) which shows the strong correlation between PAHs concentration and (1/T) in the cities of China also supports our suggestion. However, evidently, this analysis is not a conclusive one since the measurement at the cities of China used difference concentration unit for the PAHs from Seoul or Gosan. Still, it suggests the impact of local emissions vs. transport in Northeast Asia might be understood based on the relationship between the PAHs concentration and the ambient temperature and further study is warranted. Acknowledgments This work was partially supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST) (No and No ). This work was also funded by the Korea Meteorological Administration Research and Development Program under Grant RACS_ References ATSDR, Agency for Toxic Substances and Disease Registry, Toxicological profile for polycyclic aromatic hydrocarbons. Atlanta, GA, USA. Bae, S.Y., Yi, S.-M., Kim, Y.P., Temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea. Atmospheric Environment 36, BP, BP Statistical Review of World Energy June BP p.l.c., London, UK. EPA, U.S., Determination of Polycyclic Aromatic Hydrocarbons (PAHs) in Ambient Air Using Gas Chromatography/Mass Spectrometry (GC/MS), Cincinnati, OH, USA. Esteve, W., Budzinski, H., Villenave, E., Relative rate constants for the heterogeneous reactions of NO2 and OH radicals with polycyclic aromatic hydrocarbons adsorbed on carbonaceous particles. Part 2: PAHs adsorbed on diesel particulate exhaust SRM 1650a. Atmospheric Environment 40, Fang, G.C., Wu, Y.S., Chen, M.H., Ho, T.T., Huang, S.H., Rau, J.Y., Polycyclic aromatic hydrocarbons study in Taichung, Taiwan, during Atmospheric Environment 38,

7 56 J.Y. Lee et al. / Atmospheric Research 99 (2011) Goss, K.U., Schwarzenbach, R.P., Gas/solid and gas/liquid partitioning of organic compounds: critical evaluation of the interpretation of equilibrium constants. Environmental Science & Technology 32, Guo, H., Lee, S.C., Ho, K.F., Wang, X.M., Zou, S.C., Particle-associated polycyclic aromatic hydrocarbons in urban air of Hong Kong. Atmospheric Environment 37, Jones, C.C., Chughtai, A.R., Murugaverl, B., Smith, D.M., Effects of air/fuel combustion ratio on the polycyclic aromatic hydrocarbon content of carbonaceous soots from selected fuels. Carbon 42, Katz, M., Chan, C., Tosine, H., Sakuma, T., Relative rates of photochemical and biological oxidation (in vitro) of polycyclic aromatic hydrocarbons. In: Jones, P.W., Leber, P. (Eds.), Poly Nuclear Aromatic Hydrocarbons. Ann Arbor Science, MI, USA, pp Kleeman, M.J., Schauer, J.J., Cass, G.R., Size and composition distribution of fine particulate matter emitted from wood burning, meat charbroiling, and cigarettes. Environmental Science & Technology 33, Kumata, H., Takada, H., Mohamad, P.Z., Compositions of polycyclic aromatic hydrocarbons in atmospheric aerosol from China, Japan, and Malaysia (in Japanese). Research Organic Geochemistry 15, Lee, J.Y., Kim, Y.P., Source apportionment of the particulate PAHs at Seoul, Korea: impact of long range transport to a megacity. Atmospheric Chemistry and Physics 7, Lee, J.Y., Kim, Y.P., Kang, C.H., Ghim, Y.S., Kaneyasu, N., Temporal trend and long-range transport of particulate polycyclic aromatic hydrocarbons at Gosan in northeast Asia between 2001 and Journal of Geophysical Research 111, D11303 doi: /2005jd Lee, J.Y., Shin, H.J., Bae, S.Y., Kim, Y.P., Kang, C.H., Seasonal variation of size distributions of PAHs at Seoul, Korea. Air Quality, Atmosphere and Health 1, Liu, S., Tao, S., Liu, W., Liu, Y., Dou, H., Zhao, J., Wang, L., Wang, J., Tian, Z., Gao, Y., 2007a. Atmospheric polycyclic aromatic hydrocarbons in north China: a winter-time study. Environmental Science & Technology 41, Liu, X., Zhang, G., Li, J., Cheng, H.R., Qi, S.H., Li, X.D., Jones, K.C., 2007b. Polycyclic aromatic hydrocarbons (PAHs) in the air of Chinese cities. Journal of Environmental Monitoring 9, Manoli, E., Voutsa, D., Samara, C., Chemical characterization and source identification/apportionment of fine and coarse air particles in Thessaloniki, Greece. Atmospheric Environment 36, Marr, C., Dzepina, K., Jimenez, J.L., Reisen, F., Bethel, H.L., Arey, J., Gaffney, J.S., Marley, N.A., Molina, L.T., Molina, M.J., Sources and transformations of particle-bound polycyclic aromatic hydrocarbons in Mexico City. Atmospheric Chemistry and Physics 6, Okuda, T., Naoi, D., Tenmoku, M., Tanaka, S., He, K., Ma, Y., Yang, F., Lei, Y., Jia, Y., Zhang, D., Polycyclic aromatic hydrocarbons (PAHs) in the aerosol in Beijing, China, measured by aminopropylsilane chemicallybonded stationary-phase column chromatography and HPLC/fluorescence detection. Chemosphere 65, Pankow, J.F., Common y-intercept and single compound regressions of gas-particle partitioning data vs 1/T. Atmospheric Environment. Part A: General Topics 25 A, Panther, B.C., Hooper, M.A., Tapper, N.J., A comparison of air particulate matter and associated polycyclic aromatic hydrocarbons in some tropical and temperate urban environments. Atmospheric Environment 33, Park, S.S., Kim, Y.J., Kang, C.H., Atmospheric polycyclic aromatic hydrocarbons in Seoul, Korea. Atmospheric Environment 36, Park, M.H., Kim, Y.P., Kang, C.H., Ghim, S.G., Aerosol composition change between 1992 and 2002 at Gosan, Korea. Journal of Geophysical Research 109, D19S13 doi: /2003jd Simcik, M.F., Zhang, H., Eisenreich, S.J., Franz, T.P., Urban contamination of the Chicago/Coastal Lake Michigan atmosphere by PCBs and PAHs during AEOLOS. Environmental Science & Technology 31, Smith, D.J.T., Harrison, R.M., Concentrations, trends and vehicle source profile of polynuclear aromatic hydrocarbons in the U.K. atmosphere. Atmospheric Environment 30, Smith, D.J.T., Harrison, R.M., Luhana, L., Pio, C.A., Castro, L.M., Tariq, M.N., Hayat, S., Quraishi, T., Concentrations of particulate airborne polycyclic aromatic hydrocarbons and metals collected in Lahore, Pakistan. Atmospheric Environment 30, Tan, J.H., Bi, X.H., Duan, J.C., Rahn, K.A., Sheng, G.Y., Fu, J.M., Seasonal variation of particulate polycyclic aromatic hydrocarbons associated with PM10 in Guangzhou, China. Atmospheric Research 80, Tang, N., Hattori, T., Taga, R., Igarashi, K., Yang, X., Tamura, K., Kakimoto, H., Mishukov, V.F., Toriba, A., Kizu, R., Hayakawa, K., Polycyclic aromatic hydrocarbons and nitropolycyclic aromatic hydrocarbons in urban air particulates and their relationship to emission sources in the Pan-Japan Sea countries. Atmospheric Environment 39, UNEP (United Nations Environment Programme), Regionally Based Assessment of Persistent Toxic Substances, Central and North East Asia regionally report, Global Environment Facility. Vasconcellos, P.C., Zacarias, D., Pires, M.A.F., Pool, C.S., Carvalho, L.R.F., Measurements of polycyclic aromatic hydrocarbons in airborne particles from the metropolitan area of São Paulo City, Brazil. Atmospheric Environment 37, Wania, F., Haugen, J.E., Lei, Y.D., Mackay, D., Temperature dependence of atmospheric concentrations of semivolatile organic compounds. Environmental Science & Technology 32, Yassaa, N., Youcef Meklati, B., Cecinato, A., Marino, F., Particulate n- alkanes, n-alkanoic acids and polycyclic aromatic hydrocarbons in the atmosphere of Algiers City Area. Atmospheric Environment 35, Zheng, M., Salmon, L.G., Schauer, J.J., Zeng, L., Kiang, C.S., Zhang, Y., Cass, G.R., Seasonal trends in PM2.5 source contributions in Beijing, China. Atmospheric Environment 39,