Contamination of Polycyclic Aromatic Hydrocarbons Bound to PM10/PM2

PM10 (particulate matter which passes through a size selective impactor inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter) and PM2.5 were collected at four sites (A: Xiaoping, B: Huli, C: Hongwen, D: Gulang Island) from December 20, 2004 to December 29, 2004 in Xiamen. 16 Priority polycyclic aromatic hydrocarbons (PAHs) in PM10/PM2.5 were quantified by using a gas chromatograph/mass spectrometer (GC/MS). EC and OC of PM10 were analyzed by Thermal/Optical Carbon Analyzer (DRI Model 2001). Concentration, spatial distributions of PAHs and EC/OC were studied and their main sources were identified by diagnostic ratios, correlation analysis and EC/OC analysis. Among the different sampling sites, concentrations of 16PAHs were 5.20-28.07 ng/m in PM10 and 3.04-11.32 ng/m in PM2.5. Concentration of OC were 9.83-15.6 g/m and 1.41-4.73 g/m for EC associated to PM10. The main sources identified were traffic emissions and industry emission/coal combustion.


INTRODUCTION
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in the air which are well-known to be toxic, carcinogenic and mutagenic (Ames et al., 1975;MØller et al., 1982). PAHs bound to PM 10 are considered to be a great threat to the health of human beings because they could be brought into the body through breathing (Spurny, 1996). Many studies indicate that fine particles (PM 2.5 ) have greater impact on human health than coarse particles (Schwartz, 1994).
Numerous studies were focused on the concentrations and sources of PAHs bound to PM 10 /PM 2.5 in the urban air (Gao et al., 1993;Qi et al., 2000;Guo et al., 2003;Peng et al., 2003;Pan et al., 2003;Guo et al., 2004;Dallarosa et al., 2005;Ding et al., 2007) and found it was important to study the abundance, distribution and potential sources of PAHs associated to PM 10 /PM 2.5 so that the diverse effects caused by particulate matter could be efficiently controlled.
Xiamen is located along the southeastern shore of China at E117°53'-118°27', N24°25'-24°55', as shown in Fig.1. It has a population of about 1.4 million people living in a terrene-area of 1565.09 km 2 and a sea-area of 344 km 2 . It includes Xiamen Island, Gulang Island, Tongan, Jimei, Haicang, Xinglin and many other small islands, amongst which Xiamen Island has an area of 132.5 km 2 and a 234 km coastline. Xiamen has been a famous "garden city" due to its clear sky and beautiful environment, but nowadays its air quality decreased from "excellent" to "good", with the main pollutants being PM 10 . Other studies (Karar and Gupta, 2006;Valavanidis et al., 2006) showed that the highest concentrations of PAHs in particulate phase always occurred in winter. In this study, we aimed to carry out the wintertime study of concentrations, distribution patterns and main sources of PAHs bound to PM 10 /PM 2.5 in Xiamen.

Sample collection
Sampling of PM 10 and PM 2.5 were carried out at several sites (A, B, C, D) during December [21][22][23][24][25][26][27][28][29]2004 in Xiamen, Fujian province, P.R. China (Fig. 1). The sampling sites were selected to present the different functional areas: Site A: Xiaoping (N 24°51.218', E118°2.689', 900 m elevation), acted as the control site located in a forest garden to the north of Xiamen island. There is no major pollution source around 25 km area except diesel engine vehicles were used to build the road. Site B: Huli (N24°30.51', E118°6.139', 8 m elevation), as industry/traffic area. The sampling site was located on the roof of an official building, about 100 m away from a road carrying heavy traffic (1300/h, 2800/h) and surrounded by a series of industries, such as tobacco production plant, aluminium plant, building material production, etc. Site C: Hongwen (N24°28.623, E118°8.703, 15 m elevation). The sampling site was located on the roof of a middle school building which is in the center of a residential area, with no other high buildings or industry nearby. Site D: Gulang Island (N24°26.787, E118°3.819, 10 m elevation). The island is separated from Xiamen Island with a 5 min boat ride which is famous for tourism. There is no industry or traffic except for battery driven vehicles on the island. The sampling site was on the roof of a school building, about 500 m from the entrance to the island.
Daily sampling at the four sites began almost simultaneously at 10:00 a.m., with a 23 h duration. PM 10 samplers (100 L/min, Qingdao Laoshan Mechanical Corp., China) with Ø 90 mm glass fiber filters (GFFs, Whatman Corp. USA) and PM 2.5 sampler (MiliVol Airmetrics, USA, 5 L/min) with Ø 47 mm glass fiber filters (GFFs, Whatman Corp. USA) were used to collect aerosols. The samples deposited on the filters were analyzed for 16 priority PAHs, and EC/OC for PM 10 . Due to the limitation of the available PM 2.5 sampler, only two PM 2.5 samples at each site were gotten. So the following discussion was more focused on PM 10 .

Sample analysis
The glass fiber filters were pre-baked at 450 ºC for 4 h to lower their carbon blanks. GFF samples were spiked with deuterated PAHs standards (naphthalene-d 8 , acenaphthene-d 10 , acenaphthene-d 10 , chrysene-d 12 , perylene-d 12 ) prior to sample extraction. The filter was extracted with 20 mL aliquots of dichloromethane in the dark overnight, and then ultrasonically extracted for 30min at room temperature, twice. The total extract was concentrated to a volume of 1 mL by vacuum-condensing equipment. The cleanup and fractionation of the extract was done using a self-packed silica gel-Al 2 O 3 -Na 2 SO 4 column, a 5 mL acetone-rinsed burette containing 3 mL firmly packed deactivated silica gel (72-230 mesh, Sigma) in the bottom, a layer of 2 mL firmly packed deactivated Al 2 O 3 , and then 1 cm Na 2 SO 4 on the top. Ten milliliters hexane was added to condition the column. The concentrated extract was then applied to the column with an additional 3 mL hexane for complete transfer. n-Hexane was used to elute the n-alkanes fraction (5 mL, F1), benzene: n-hexane (v/v, 1:1) was used to elute the aromatic fraction (10 mL, F2). The volume of each fraction was concentrated to near dryness by vacuum-condensing equipment, and then fixed to 100 μL. The PAHs in F2 fractions were analyzed by GC-MSD (HP 6890 GC-HP 5973 MSD) in Selected Ions Mode (SIM). The GC was equipped with a HP-5 MS capillary column (30 m × 0.25 mm i.d., film thickness 0.25 m), with helium as carrier gas. The oven temperature program was as follows: hold at 60ºC for 2 min, increased to 120ºC at a rate of 4ºC/min, then increased to 300ºC at a rate of 3ºC/min and a final hold at 300ºC for 10 min. The injector and detector temperature were 250ºC and 280ºC. 1 μL sample was injected in a splitless model. The mass scanning ranged between 50 and 500 m/z.
16 PAHs were quantified in SIM mode according to their elution orders as followed: naphthalene (Nap, m/z = 128), acenaphthylene (Ace, m/z = 152), acenaphthene (Acen, m/z = EC/OC were analyzed by National Environmental Analysis Center using Thermal/Optical Carbon Analyzer (DRI Model 2001) with the method detection limits (MDL) of 0.82 μg C/cm 2 for OC and 0.19 μg C/cm 2 for EC.

Quality control
The analytical method was based on the USEPA Method TO-13 (US EPA, 1999). Field blanks, filter blanks and solvent blanks were analyzed by the same procedure as the samples and ensured that there were no significant background interferences with only trace amount of PAHs being detected out (ND-5.13 ng). When compared with the amount (160.94-748.88 ng) in the real samples, the concentration in blank samples could be neglected.
The quantifications were performed using the internal standard method. The recovery test was performed by spiking known amounts of a mixture of PAHs onto the GFFs and then the spiked filter was treated the same way as mentioned above. Method detection limit (MDL) was calculated taking into account 3 times the ratio of the heights obtained for noise. Recovery efficiency of PAHs ranged from 60.1% to 119.8%. Method detection limits were between 1.5 × 10 -3 ng/m 3 (BkF) and 11.4 × 10 -3 ng/m 3 (Nap), as shown in Table 1.

Comment on meteorology and PAHs concentrations
The meteorological conditions and air pollution index during the sampling periods were shown in Table 2. Temperature was about 8-20 , wind speed was almost higher than 2 m/s and relative humility was high (71%-92%) which were the typical subtropical climate. The relationship between different PAHs bound to PM 10 and meteorology parameters were analyzed by SPSS packages (Table 3). PAHs have inverse correlation with relative humidity (-0.538) and weak correlations with temperature (r = 0.34) or wind speed (r = 0.42) (p < 0.05). But PM 10 has significant correlation with temperature with r = 0.74 (p < 0.05) while inverse correlation with wind speed (r = -0.005) and RH (r = -0.20). Thus is consistent with results observed by Karar and Gupta (2006) in Kolkata, India and Mantis et al. (2005) in the Greater area of Athens, Greece. When relative humidity increases, the fine particulates have more chances to aggregate together and grow bigger, the concentration of PM 10 decreased and also of PAHs bound to PM 10 . Conc. = concentration, Temp. = temperature, RH = relative humidity.
In Xiamen, 16 PAHs were detected out in all samples except that Ace was below the detection limit (Table 4). In PM 10 , the concentration range of individual PAHs was from ND-13.31 ng/m 3 and 5.20-28.07 ng/m 3 for 16PAHs. The highest concentration of 16PAHs almost occurred in the first sampling day (Dec. 20) at different sites. From the second sampling day, the variation of total concentrations was not much suggesting the stable pollution level under similar meteorology conditions. Among PAHs, Phen  Compared with other cities in China, concentration of PAHs associated to PM 10 in Xiamen was significantly lower than those in inland cities, such as Beijing (116.0 ng/m 3 for annual average concentration) (Zhou et al., 2005) and Shanghai (245.52 ng/m 3 for winter) (Guo et al., 2004), but in the similar level as the southern coastal cities including Guangzhou (55.49 ng/m 3 for winter and spring), Hongkong (14.88 ng/m 3 for winter and spring) and Macao (41.70 ng/m 3 for winter and spring) (Qi et al., 2000), etc. One of the most obvious reasons for this is that central or residential heating in winter is a major pollution source in the northern inland cities (Beijing, etc.) while southern cities do not have this pollution source. Compared with overseas cities, concentration of PAHs in Xiamen was lower than that in New Delhi Sharma et al., 2003 , but in the same level of that in some coastal cities, such as Naples (Caricchia et al., 1999), Athens (Mantis et al., 2005) and Santiago (Romero, 2002), etc.
Concentration of BaP is an indicator for the control of PAHs in the atmosphere. Its acceptable concentration limit is 10 ng/m 3 based on the Chinese standard (GB3095-1996). The concentrations of BaP in PM 10 and PM 2.5 were in the range 0.10-1.34 ng/m 3 meaning that the PAHs pollution was not serious in Xiamen.
For better quantification of whole carcinogenicity from whole PAH fraction, "BEQ" (Benzo[a]pyrene Equivalence) was introduced as an index and calculated by the following formula using the toxic equivalency factors (TEFs) of the individual PAHs Robert et al., 1999 and their concentrations: The BEQ index was 0.85 and 0.92 for PAHs in PM 10 and PM 2.5 in Xiamen which was much lower than that of Shanghai (15.77) (Guo et al., 2004), but in the same level of that in some Japanese cities (1.91) (Takeshi et al., 2004).
Relationship of concentration of PAHs and concentration of PM 10 was analyzed by SPSS (Table 3). Results showed that there were significant correlation (r = 0.71, p < 0.01, n = 35 between the concentration of PAHs and PM 10 . These results suggested that sources of PM 10 and PAHs in the air were similar, and the control of PM 10 .was an effective way to decrease the PAHs pollution level in the air as well.

Distribution of PAHs bound to PM 10 /PM 2.5
Among different function areas, there were some difference existed in the concentration and distribution patterns of PAHs in PM 10 /PM 2.5 (Fig. 2-Fig. 5, Table 4). The concentration ranges and standard deviation of 16PAHs bound to PM 10 at different sampling sites were as follows: B: 11.0-28.1 ng/m 3 (16.1 ± 5.1 ng/m 3 ) > D: 7.8-21.1 ng/m 3 (11.2 ± 4.1 ng/m 3 ) > C: 6.6-13.5 ng/m 3 (8.4 ± 2.5 ng/m 3 ) > A: 5.2-11.5 ng/m 3 (6.9 ± 2.0 ng/m 3 ), respectively. The concentration of 16PAHs bound to PM 2.5 showed the same patterns: B (11.32 ng/m 3 ) > D (5.59 ng/m 3 ) > C (5.54 ng/m 3 ) > A (3.04 ng/m 3 ).    In PM 10 and PM 2.5 , the highest concentration of 16PAHs always occurred at site B (industry/traffic area) which was quite related to its environmental conditions. Site B was 100 m away from the main line carrying heavy traffic (1300/h, 2800/h) and also surrounded by a series of industries, such as tobacco production plant, aluminium smelting plant, etc. Large amount of industry and traffic emissions made the concentration of PAHs highest at this site. Among PAHs, Flu and Phen covered much more of total PAHs at this site than at other sites in PM 10 . This was consistent with the fact that this area was a dense traffic area with more contribution of heavy-duty vehicles emissions (Marr et al., 1999;Rogge et al., 1993). In PM 2.5 , BaP, Indo and BgP covered more of 16PAHs at site B than at other sites meaning that there is more contribution from gasoline vehicles (Simicik et al. 1999) at site B. The concentration of PAHs at site D (Gulang Island) was ranked second. Though there was no direct automobile emission or industry emission, the heavy ship traffic to this famous tourist island and the wind bringing with the particulates from the southwest SongYu coal-generating electricity plant and the influence of the heavy road traffic emissions from the thither area could not be neglected. Site A (forest garden area) and site C (residential area) were relatively clean which were in consistent with the fact that there were no heavy traffic or industry nearby. Also plants could effectively clean out PAHs in the atmosphere (Simonich et al., 1994).
Though the concentration of PAHs was quite different, the distribution patterns of PAHs bound to PM 10 in different function areas were quite similar. At all sites, 3-4 ring PAHs including Phen (39.2%-51.2%), Flu (5.7%-10.4%), Pyr (10.9%-11.8%) and Chry (5.0%-7.9%) were the dominant PAHs components bound to PM 10 (Fig. 4). These four PAHs covered 60.8%-81.3% of 16PAHs. These distribution profiles were quite different from many other cities (Papageorgopoulou et al., 1999;Caricchia et al., 1999;Chetwittachan et al., 2002;Pan et al., 2003;Christine et al., 2005), but similar with that in Athens, Greece which pointed out the great contribution from traffic emissions (Valavanidis, 2006). In PM 2.5 , some higher molecular weight PAHs such as BaP (5.3-11.8%), Indeo (4.7-11.5%), BgP (5.4-13.4) covered more than that of PM 10 . Among low and middle molecular PAHs, Phen was the dominant component which covered 12.3-38.2% of 16PAHs, Pyr, Chry and Fluo covered 12.5-25.9%, 9.1-19.1% and 3.5-8.1% of 16PAHs, respectively. SPSS packages were used to detect the correlation of distribution patterns of individual PAHs at different sampling sites. Results showed that there was no significant difference in the distribution of PAHs in different function areas (Table 5). In PM 10 , all the values of correlation coefficient (r) were much higher than 0.9 (P = 0.01) meaning that the sources of PAHs were quite similar at different sampling sites. In PM 2.5 , all the values of r were higher than 0.50, in which values of 0.95, 0.84 and 0.76 were for PAHs at site B and C, A and D, A and C, respectively. Thus could be explained by the fact that Xiamen was a coastal city with relative simple energy structure and the wind from the sea could better dilute and diffuse the pollutants in the air.

Diagnostic ratio
PAHs have been used as tracers to distinguish between diverse sources (Venkataraman and Friedlander, 1994;Mandalakis et al., 2002;Guo et al., 2005). Different profiles and distribution patterns of individual PAHs were characteristic of different pollution sources. As a result of numerous studies, Kulkarni and Venkataraman (2000) identified some PAHs as tracers of several sources in the urban atmosphere: Phen, Fluo and Pyr are characteristic of coal combustion; Pyr, Phen, Fluo are derived from incineration processes; BaP and Fluo are tracers for wood combustion; BgP and Indeo for vehicular fuels; and Fluo, Pyr, BbF and BkF for heavy-duty diesel vehicles. The main PAHs sources in the Asian area were traffic exhausts (Acen, Fluo, Flu, Pyr, Chry, BeP) and industrial emissions (BaP, BaA, BeP, Cor) (Chang et al., 2005).
The sum of the concentrations of the nine following combustion PAHs (CPAHs): Fluo, Pyr, BaA, BbF, BkF, BaP, BeP, Indeo and BgP has often been used as a characteristic diagnostic parameter for PAHs produced by stationary combustion sources (Rogge, 1993;Kavouras, 1999;Bi et al., 2002;Manoli et al., 2002;Sienra, 2005), Rogge et al. (1993) determined the value of CPAHs/ PAHs ratio for non-catalyst (0.4) and catalyst-equipped (0.5) automobiles and for heavy-duty diesel trucks (0.3). In this study, the value of CPAHs/ PAHs in PM 10 was 0.3-0.4 meaning that stationary combustion sources (industry emission) was a contributor for the PAHs pollution in the air. In PM 2.5 , its value was 0.4-0.7 meaning that stationary combustion sources contribute much more than that at PM 10 . Lee et al. (1977) suggested value of Fluo/Pyr for coal combustion (1.4) and for wood burning (1.0) and for fuel combustion (<1). Gschwend et al. (1981) indicated value of BaA/Chry ratio was 0.93 for wood burning and 0.28-1.2 for gasoline combustion and 0.17-0.36 for coal combustion. In this study, the values of Fluo/Pyr both in PM 10 and PM 2.5 were 0.20-0.39 indicating the fuel combustion source especially traffic emissions source was a great contributor; BaA/Chry in PM 10 was 0.18-0.50 meaning the gasoline and diesel vehicles emission sources. Thus most of the diagnostic ratios in PM 10 and PM 2.5 suggested the significant contribution of gasoline exhaust and diesel exhaust, with some contribution from coal and wood combustion sources.

OC/EC and inorganic analysis
Carbonaceous particles consist of two major components, elemental carbon (EC) and organic carbon (OC), the sum of them being defined as total carbon (TC). Elemental carbon (EC) was associated with primary emission from fossil fuel combustion and wood burning. Because of its stability in the atmosphere, EC was usually used as the marker for anthropogenic pollution.
Organic carbon (OC) can be emitted directly from the emission sources or produced from atmospheric transformation of organic gases. Secondary OC is formed by condensation of low vapor pressure products during photo-oxidation of hydrocarbons (Seinfeld et al., 1998;Chow et al., 1996).
In this study, OC/EC in PM 10 was analyzed. Concentrations of OC were in the range of 9.83-15.60 g/m 3 and 1.41-4.73 g/m 3 for EC in Xiamen .
Results showed the secondary OC covered 38.1% in average of the total OC in Xiamen atmosphere. Generally, these results could be explained by the mild meteorology conditions with high temperature and good sunshine even in winter. They were quite suitable for the photochemical reactions to generate the SOC. The differences among sites were quite consistent with the fact that the pollutants at site B were more contributed by the continuous fresh input from traffic emission and industry emission while site A and D were more contributed by the secondary pollution due to the lack of the primary emission sources.
Concentration of PAHs and OC significantly correlated with r = 0.59 (p < 0.01) while correlation coefficient between EC and OC was 0.80 (p < 0.01). Thus meant EC and OC were from similar sources (Offenberg et al., 2000). In conjunction with the results of the high accumulation level of S, Se, Zn and Br in PM 10 .by the elemental and inorganic analysis , the mixing pollution sources of coal combustion/industry emission and serious traffic emissions were identified.

CONCLUSIONS
Wintertime study of atmospheric concentration of 16PAHs bound to PM 10 /PM 2.5 , EC/OC were carried out during Dec. 21, 2004-Dec. 29, 2004. Concentrations of 16PAHs were 5.20-28.07 ng/m 3 in PM 10 and 3.04-11.32 ng/m 3 in PM 2.5 . Concentration of OC was 9.83-15.6 g/m 3 and 1.41-4.73 g/m 3 for EC. The highest concentration of 16PAHs always occurred at site B meant the industry emission and traffic emission were great contributor for PAHs pollution in Xiamen. Ratio analysis, EC/OC analysis and correlation analysis suggested the main sources of PAHs in PM 10 /PM 2.5 were traffic emissions, industry emission and coal combustion.