Transported and Local Organic Aerosols over Fukuoka, Japan

In order to understand transported and local pollution in an urban area that are strongly affected by long-range transport of air pollution, daily concentrations of 15 polycyclic aromatic hydrocarbons (PAHs) and 20 n-alkanes in the total suspended particles were simultaneously measured at sites in Western Japan on Fukue Island (FI), located downwind of mainland East Asia, and Fukuoka City (FC), a megacity close (< 200 km) to the FI site, in spring and winter 2010 and summer 2011. The average total PAH concentration observed at the FC site (2.93 ± 2.17 ng/m) was higher than that at the FI site (1.78 ± 1.70 ng/m). The average total n-alkane concentration at the FC site (34.7 ± 21.8 ng/m) was also higher than that at the FI site (12.2 ± 9.2 ng/m). However, the total PAH and n-alkane concentrations measured at the FI site were considerably high, despite its remote location. The seasonal changes in the specific PAH ratios, used to determine the source of pollutants, were similar between the FC and FI sites. The average fluoranthene/(fluoranthene + pyrene) ratio was 0.57–0.65 in winter and spring and 0.48–0.51 in summer. PAHs observed at both sites mainly originated from coal or biomass combustion in spring or winter, whereas those were affected by petroleum combustion as well as coal and biomass combustion in summer. These field results show that pollutants transported from mainland East Asia make a significant contribution to the total PAHs and n-alkanes at the FC site in the winter and spring seasons.


INTRODUCTION
Emissions of air pollutants from mainland East Asia have increased in recent decades with the rapid economic growth in this area (Ohara et al., 2007).In recent years, long-range transport of air pollutants has often been observed around the East China Sea and the Japan Sea regions in winter and spring (Lin et al., 2007;Takami et al., 2007;Yang et al., 2007;Hatakeyama et al., 2011;Lai et al., 2011;Kwon et al., 2012).The emissions of carbonaceous aerosols, for example, particulate polycyclic aromatic hydrocarbons (PAHs) and n-alkanes, have also increased (Su et al., 2006;Zhang and Tao, 2009;Inomata, 2012).PAHs are harmful compounds.According to International Agency for Research on Cancer (2012), benzo(a)pyrene is carcinogenic, and dibenz(a,h)anthracene is probably carcinogenic.The maximum total PAH levels observed during air pollution events at Cape Hedo on Okinawa Island were comparable with the average total PAH levels measured at urban sites (Sato et al., 2008;Yoshino et al., 2011), indicating that transported and local pollutants would make comparable contributions to the atmosphere of megacities around this area.
Recently, Kaneyasu et al. (2010Kaneyasu et al. ( , 2011) ) observed the concentrations of PM 2.5 (fine particles in the ambient air 2.5 µm or less in size) simultaneously at sites in Western Japan on Fukue Island (FI), located downwind of mainland East Asia, and Fukuoka City (FC), a megacity close (< 200 km) to the FI site.It is expected that air pollutants transported long distances are the main source of pollutants observed at the FI site since no major emissions occur on or near this island, whereas both transported and local pollutants are observed at the FC site.Kaneyasu et al. (2010Kaneyasu et al. ( , 2011) ) concluded that PM 2.5 observed at the FC site is mainly attributable to transported pollutant because the year-round time-series of PM 2.5 concentration observed at the FC site was very similar to that observed at the FI site.Ogawa et al. (2012) observed particulate PAHs simultaneously at the FC and FI sites in spring 2009.The specific PAH ratios used to determine the source of pollutants observed in this previous study showed that the emission sources of particulate PAHs observed at the FC site were very similar to those at the FI site.
In this study, particulate PAHs and n-alkanes were simultaneously observed at the FI and FC sites employing a similar approach to that used by Kaneyasu et al. (2010Kaneyasu et al. ( , 2011)).The seasonal changes in the PAH and n-alkane concentrations at the FC and FI sites are newly observed in this study.The aims of this work were to determine the contributions of transported pollutants to the total concentrations of PAHs and n-alkanes observed at the FC site and to elucidate the seasonal change in these contributions.

Aerosol Sampling
As shown in Fig. 1, the FI site (32.8°N,128.7°E) is located 1,460 km southeast of Beijing and 740 km east of Shanghai (Takami et al., 2005).According to the Japanese census of 2010, the population of Fukue Island is approximately 40,000.The FI site is 20 km west of a single downtown of the island.There are no major sources of emissions around the observation site.The FC site (33.6°N,130.4°E) is located 190 km east of the FI site.According to the Japanese census of 2010, Fukuoka City has a population of 1.5 million, and Greater Fukuoka (consisting of Fukuoka City and Kitakyushu City) has a population of 2.5 million.Specifically, the FC site was set on the rooftop of the five-floor Faculty of Science building of Fukuoka University, which is located at the south of downtown Fukuoka.An expressway is located 500 m south of the site.The observation periods were 22 days in March and April 2010, 15 days in December 2010 and 10 days in July and August 2011.The average temperature, relative humidity, wind speed and total suspended particle (TSP) concentration measured during each observation period are listed in Table 1.
At each site, TSPs were collected on a quartz-fiber filter using a high-volume air sampler (HV-1000F, Shibata, Tokyo, Japan).Before sampling, quartz-fiber filters (QR-100, Advantec, Tokyo, Japan) were heated at 773 K for 4 h.The flow rates of samplers were 1 m 3 /min.Filters at both sites were changed daily.Filter samples were transported from observation sites to a laboratory and were stored at 255 K until pretreatment prior to analysis.

Aerosol Sample Pretreatment
Each sample filter was spiked with a 100-μL isooctane solution containing a mixture of naphthalene-d 8 , anthracened 10 , p-terphenyl-d 14 and benz(a)anthracene-d 12 (5 ppm each) as surrogates for the evaluation of PAH recovery.The filter sample was then cut into ca. 2 × 0.5 cm pieces.These filter pieces were sonicated in 50-70 mL of dichloromethane three times and then sonicated in 60 mL of methanol two times to extract organic materials.Each sonication lasted 20 min.All dichloromethane and methanol extracts were placed together in a 300-mL flask and concentrated to ca. 3 mL at a pressure of 213-533 hPa at 304 K in a rotary evaporator Büchi Corporation,Flawil,Switzerland).Insoluble particles were removed from the concentrated extract using a Teflon syringe filter (0.2 μm pore size, Whatman, Maidstone, UK).The filtered extract was then placed in a 20-mL glass amber vial and was re-concentrated to near dryness under a gentle stream of dry nitrogen gas.The re-concentrated extract was then dissolved in 1.0 mL of n-hexane.
The n-hexane solution of each aerosol sample was fractionated into five polarity fractions using a flash chromatograph (Isolute VacMaster-10, Biotage AB, Uppsala, Sweden).The procedure of fractionation is described in detail elsewhere (Sato et al., 2008).PAHs and n-alkanes were both contained in the first fraction of the n-hexane solution.This fraction was placed in a 1.5-mL glass amber vial and concentrated to near dryness under a gentle stream of nitrogen gas.As internal standards for the evaluation of PAH signal intensities, a 100-μL isooctane solution containing a mixture of acenaphthene-d 10 and chrysene-d 12 (5 ppm each) was added to the 1.5-mL vial containing the concentrated sample.This solution was used for the analysis of PAHs.For use as n-alkane analytical samples, a 50-μL aliquot of each PAH analytical sample was placed in a 1.5-mL glass amber vial and concentrated to near dryness under a gentle stream of nitrogen gas.As internal standards for the evaluation of n-alkane signal intensities, a 50-100-μL 5ppm isooctane solution of 17β(H),21β(H)-hopane was added to the 1.5-mL vial containing the concentrated n-alkane sample.This solution was used for n-alkane analysis.

GC/MS Analysis of Aerosol Samples
Each analytical sample was analyzed by gas chromatography/mass spectrometry (GC/MS).A 1-μL aliquot of analytical sample was injected into a GC/MS instrument (6890N GC instrument combined with 5973 Network Mass Selective Detector, Agilent Technologies, Palo Alto, CA, USA) in splitless mode.The temperature of the injection port was 583 K.The injected sample was separated by a capillary column (Agilent J & W HP-5MS; length = 30 m, diameter = 250 μm, film thickness = 0.25 μm, Agilent Technologies, Palo Alto, CA, USA).Helium was used as the carrier gas.The flow rate of the carrier gas was 1.0 mL/min.The column temperature was maintained at 343 K for 2 min, increased to 423 K at 30 K/min, then to 583 K at 4 K/min, and finally maintained at 583 K for 10 min.The separated analytes were introduced into the mass spectrometer and were ionized by electron ionization.Fifteen PAHs with three to seven rings (Table 2) and twenty n-alkanes with 14 to 33 carbon atoms (Table 3) were monitored using the selected-ion monitor method.
Quantified results of PAHs were corrected taking into account the recoveries determined using internal surrogate standards.On the other hand, quantified results of n-alkanes were corrected taking into account the recoveries measured by separate analysis of five filters spiked with the sample mix.In this study, two or three field blank samples, which were treated in a similar manner to the aerosol samples but were not used for aerosol sampling, were prepared during each observation period.No PAH contamination was detected on any of these blank filters.On the other hand, low levels of n-alkane contamination were detected on the blank samples, although these were much lower than those present on any aerosol samples.The n-alkane contaminant concentrations in each observation period were evaluated from the averages of two or three blank results and were then subtracted from the results of n-alkanes.For validation of the analytical protocol used in this study, PAHs present in a standard reference sample (NIST SRM 2585, organic contaminants in house dust) were analyzed four times following the protocol used in this work.The average PAH concentrations agreed with certified values.

Statistical Analysis of Average Data
In this study, t-tests were performed for comparisons between two average values.At first, F-test on two data sets was carried out to determine whether the variances of the two data sets were homogeneous (p > 0.05).If the variances of the two data sets were homogeneous, Student's t-tests were performed to determine whether the difference between two average values was significant (p < 0.05).Otherwise, Welch's method was employed.

Air Mass Trajectory Calculations
Four-day backward air mass trajectories from the FI and FC sites during the entire period of study were calculated using the NOAA HYSPLIT model (Draxler and Rolph, 2012).Trajectories were calculated at altitudes of 500, 1,000, and 1,500 m above sea level at the middle of each filter sampling period.

Polycyclic Aromatic Hydrocarbons
Table 2 shows average PAH concentration distributions measured during each observation period at the FC and FI sites.In Table 2, the abbreviations used in this article for PAH molecules are also shown.At both sites and in all seasons, the PAHs present at high levels were PHE, FLT, PYR, CHR, BbF, IcdP, BeP and BghiP.Generally, these PAHs are abundant in particles collected in urban air.The average value of ΣPAHs (the total atmospheric concentration of 15 PAHs) measured during the entire period of study at the FC site (2.93 ± 2.17 ng/m 3 ) was higher than that measured at the FI site (1.78 ± 1.70 ng/m 3 ) (p < 0.05).However, the value for the FI site was considerably high, despite its remote location.
Fig. 2 shows the day-to-day variation of ΣPAHs measured during the entire period of study at the FC and FI sites.It is expected that PAHs transported long distances are the main contributors to pollution at the FI site, whereas both transported and local PAHs are present at the FC site.This is supported by the fact that the result of ΣPAHs observed at the FC site was close to or higher than that observed at the FI site on the same day.Using the obtained results, daily ratios of FI ΣPAHs to FC ΣPAHs were calculated.This ratio is presumed to be an index that reflects the contribution of transported pollutants to the total PAHs measured at the FC site.The average value of spring (0.657 ± 0.399) or winter 2010 (0.745 ± 0.201) was higher than that of summer 2011 (0.273 ± 0.315) (p < 0.05 in both comparisons).The results of the spring and winter seasons indicate that 65 to 75 % of total PAHs observed at the FC site are transported, whereas 25 to 35 % of total PAHs observed at the FC site are emitted from local  Sato et al. (2008) and Ogawa et al. (2012) measured the same 15 PAHs around the East China Sea.The averages ΣPAHs observed at the FI site in spring and fall 2009 were reported to be 1.71 and 2.17 ng/m 3 , respectively (Ogawa et al., 2012).The average value of ΣPAHs observed at Cape Hedo on Okinawa Island between 2005 and 2008 was reported to be 1.6 ng/m 3 (Sato et al., 2008).These values observed at island sites around the East China Sea are very close to the average ΣPAHs observed at the FI site in this study.The average value of ΣPAHs observed at the FC site in spring 2009 was reported to be 5.31 ng/m 3 (Ogawa et al., 2012) and was close to or slightly higher than that observed at the FC site in this study.The average values of ΣPAHs observed at the FI and FC sites in this study were lower than those observed in Chinese cities.For example, Wang et al. (2006) observed the total concentrations of 18 PAHs at 14 Chinese cities.They reported that the total PAH concentrations in the winter in 2003 were 14 to 701 ng/m 3 .Fig. 3 shows seasonal changes in the FLT/(FLT + PYR) ratio used to determine the source of pollutants measured at the FI and FC sites.In Fig. 3, average (ave), median, standard deviation (σ), maximum (max) and minimum (min) values of the FLT/(FLT + PYR) ratio measured in each season at each site are shown.The FLT/(FLT + PYR) ratio is higher than 0.50 when PAHs emitted from coal or biomass  combustion are present, whereas it is lower than 0.50 when PAHs are emitted from petroleum combustion (Yunker et al., 2002;Lima et al., 2005;Liu et al., 2007).Liu et al. (2007) reported that the FLT/(FLT + PYR) ratio was higher than 0.50 in winter in North China, indicating that PAHs observed in winter in this area are mainly emitted from coal or biomass combustion.The average ratio of FLT/ (FLT + PYR) measured in spring at FI (0.60 ± 0.02) was close to that measured in winter at FI (0.61 ± 0.01) (p > 0.05), and was higher than that measured in summer at FI (0.51 ± 0.04) (p < 0.05).A similar seasonal change in the ratio of FLT/(FLT + PYR) was also observed at the FC site.The ratio of FLT/(FLT + PYR) measured at the FC site was slightly lower than that measured at the FI site in spring (p < 0.05) or winter (p < 0.05), but the difference observed between the two observation sites in spring or winter was much smaller than that observed between spring and summer at the FC or FI site.These results indicate that PAHs measured at both sites mainly originated from coal or biomass combustion in spring or winter, whereas those measured at both sites were affected by petroleum combustion as well as coal and biomass combustion in summer.It is likely that PAHs measured at both sites in spring and winter are strongly influenced by emissions from mainland East Asia.
Another PAH ratio used for the estimation of emission sources is the IcdP/(IcdP + BghiP) ratio.The IcdP/(IcdP + BghiP) ratio is higher than 0.50 for PAHs emitted from coal or biomass combustion and lower than 0.50 for PAHs emitted from petroleum combustion (Liu et al., 2007;Lima et al., 2005;Yunker et al., 2002).That is, the IcdP/(IcdP + BghiP) ratio is very similar to the FLT/(FLT + PYR) ratio.As shown in Table 2, the IcdP/(IcdP + BghiP) ratio measured in summer at FC was lower than that measured in spring (p < 0.05) or winter at the same site (p < 0.05).Similar results were also obtained at the FI site.These results mirrored those obtained for the FLT/(FLT + PYR) ratio.
The BaP/BeP ratio is used as an index of the photochemical aging of PAHs (Gogou et al., 1996 , 1987).The BaP/BeP ratio decreases with an increasing extent of photochemical aging.The BaP/BeP ratio observed in Beijing, an area with one of the highest levels of PAH emission globally, is close to 1 (Okuda et al., 2006;Wang et al., 2006).As shown in Table 2, the average BaP/BeP ratio measured at the FI site during the entire period of study (0.64 ± 0.13) was slightly lower than that measured at the FC site during the same time period (0.73 ± 0.12).As these values are lower than 1, it is suggested that the pollutants at these site have already undergone photochemical aging over a substantial period of time.PAHs observed at both the FC and FI sites are mainly transported from regions other than both sites.The BaP/BeP ratio at the FC site was slightly higher than that at the FI site.This result suggests that the total PAH concentration emitted from local emission sources in Fukuoka City has a minor contribution to the total PAH concentration observed at the FC site.Ogawa et al. (2012) reported that BaP/BeP ratios measured at the FI and FC sites in spring 2009 were 0.71 ± 0.07 and 0.67 ± 0.08, respectively.Their results were similar to those observed at the same sites in this study.Sato et al. (2008) reported that the average BaP/BeP ratio observed at Cape Hedo on Okinawa Island between 2005 and 2008 was 0.47, which was lower than that observed at the FI site in this study.If a substantial amount of time has passed since the PAHs observed at the FI or FC site were emitted, the FLT/(FLT + PYR) and IcdP/(IcdP + BghiP) ratios measured at these sites might also be affected by photochemical aging.Mascret et al. (1986) reported the relative decay rates of PAHs in the atmosphere, D(X), where X represents a specific PAH compound.According to their results, there is the following relationship: D(BaP)/D(BeP) (= 2.3-2.7)> D(IcdP)/D(BghiP) (= 0.78-1.0)> D(FLT)/D(PYR) (= 0.59-0.67).The differences between the ratios indicate that the extent of the effect of photochemical aging depends on the PAH ratio.Similar conclusions on the sources of PAH emissions were obtained using the FLT/(FLT + PYR) and IcdP/(IcdP + BghiP) ratios in this study, indicating that the effects of photochemical aging on the ratios of FLT/(FLT + PYR) and IcdP/(IcdP + BghiP) are negligible here.

n-Alkanes
Table 3 shows seasonal changes in the average n-alkane concentration distribution measured at the FC and FI sites.The n-alkane distribution observed in spring at FC shows that the concentration of C 19 n-alkane was the highest.According to Young et al. (2002), C 19 n-alkane is emitted from gasoline or diesel vehicles.Therefore, the results in spring at FC are likely to have been affected by local sources of emission around the observation site.C 25 , C 29 and C 31 n-alkanes are the most abundant molecules in the other seasons at the FC site and in all seasons at the FI site.Among particulate n-alkanes emitted from anthropogenic sources, C 25 is often the most abundant component (Young et al., 2002).C 29 and C 31 n-alkanes originate from plant wax (Yamamoto and Kawamura, 2011).The average value of Σalkanes (the total concentration of 20 n-alkanes) measured at the FC site during the entire period of study (34.7 ± 21.8 ng/m 3 ) was higher than that measured at the FI site during the same period (12.2 ± 9.2 ng/m 3 ) (p < 0.05).
Fig. 4 shows the day-to-day variation of Σalkanes measured at the FC and FI sites.The value of Σalkanes at the FC site was close to or higher than that observed at the FI site on each day.The average ratios of FI Σalkanes to FC Σalkanes in spring, winter and summer were 0.404 ± 0.192, 0.352 ± 0.179 and 0.379 ± 0.247, respectively, and did not differ significantly throughout the year (p > 0.05).The results of the spring and winter seasons indicate that 35 to 40 % of total n-alkanes observed at the FC site are transported, whereas 60 to 65 % of total n-alkanes observed at the FC site are emitted from local emission sources.
Fig. 5 shows the seasonal changes in n-alkane carbon preference index (CPI) measured at the FC and FI sites.CPI is defined as the ratio of the total concentration of all n-alkanes with an odd number of carbons to that of nalkanes with an even number.The CPI index is close to 1 for n-alkanes emitted by the combustion of fossil fuels and is higher than 5 for plant wax n-alkanes from vegetation (Yamamoto and Kawamura, 2011).The CPI value measured in winter at FI (1.63 ± 0.14) was lower than those measured in spring (3.00 ± 0.74) (p < 0.05) and summer at the same site (3.22 ± 1.86) (p < 0.05).Similar results were observed at the FC site.These results indicate that the contribution of plant wax to the total concentration of nalkanes increased in spring and in summer at both sites.
In this study, C 19 n-alkane observed in spring at FC was attributed to anthropogenic pollutants.The (C 31 + C 33 )/(C 22 + C 24 ) ratio (not related to the level of C 19 n-alkane) was also used as an alternative index reflecting the sources of n-alkane.The (C 31 + C 33 )/(C 22 + C 24 ) index also increases with an increasing contribution of plants to the total concentration of n-alkanes (Yamamoto and Kawamura, 2011).As shown in Table 3, the average value of the (C 31 + C 33 )/(C 22 + C 24 ) ratio measured in winter at FI (0.91 ± 0.25) was lower than those in spring (2.22 ± 1.31) (p < 0.05) and summer at the same site (7.60 ± 6.63) (p < 0.05).Similar results were also observed at the FC site.These results support the above-mentioned conclusions about the seasonal change in the source of n-alkanes drawn from the CPI values obtained in this study.

Air Mass Trajectory Calculations
The results of the backward air mass trajectories from the FI and FC sites are shown in Fig. 6.In this figure, black curves indicate trajectories toward the FC site, while red curves indicate trajectories toward the FI site.Transport from the Asian mainland dominated in the spring and winter (Figs. 6(a), 6(c), and 6(e)), whereas that from the Pacific Ocean dominated in the summer (Figs. 6(b),6(d), and 6(f)).The trend of the seasonal change in source regions was independent of the altitude of trajectory between 500 and 1,500 m.These results indicate that pollutants observed at the FI site and transported pollutants observed at the FC site are mainly attributable to those transported from the Asian mainland in the spring and winter, but to those transported from other parts of Japan in the summer.
Pollutants observed at the FI site might also be transported from downtown Fukue Island and Fukuoka City.According to preset results of trajectory calculations, transport from mainland East Asia is predominant in the winter and spring seasons.In these seasons, transport from downtown Fukue Island or Fukuoka City to the FI site is minor because both downtown Fukue Island and Fukuoka City are located downwind of the FI site.In contrast, air pollutants are transported not only from other parts of Japan but also from downtown Fukue Island and Fukuoka City in the summer season.In the summer season, the contribution of the transported pollutant to the total pollutant observed at the FC site will be lower than the observed FI/FC ratio.

CONCLUSIONS
In this study, daily concentrations of particulate PAHs and n-alkanes present in TSPs were simultaneously observed at the FI and FC sites in spring and winter 2010 and summer 2011.The seasonal changes in the PAH and n-alkane concentrations were newly observed at the FC and FI sites in this study.The ratio of FI ΣPAHs to FC ΣPAHs measured in spring (0.66 ± 0.40) or winter (0.75 ± 0.20) was higher than that measured in summer (0.27 ± 0.32).The seasonal changes in the PAH ratio of FLT/(FLT + PYR) were similar between the FC and FI sites.PAHs observed at both sites mainly originated from coal or biomass combustion in spring or winter, whereas those were affected by petroleum combustion as well as coal and biomass combustion in summer.The ratios of FI Σalkanes to FC Σalkanes measured in spring (0.40 ± 0.19), winter (0.35 ± 0.18) and summer (0.38 ± 0.25) did not differ significantly.The results of backward trajectory calculations indicate that pollutants observed at the FI site and transported pollutants observed at the FC site are mainly transported from the Asian mainland in spring and winter, but from other parts of Japan in summer.The results of the present field observations show that transported pollutants make a significant contribution to total PAHs and n-alkanes measured in Fukuoka City, a megacity located downwind of mainland East Asia, in the winter and spring seasons.

Fig. 1 .
Fig. 1.Location of the two observation sites in this study.

Fig. 3 .
Fig. 3. Seasonal changes in FLT/(FLT + PYR) ratio used to determine the source of pollutants measured at Fukuoka City (FC) and Fukue Island (FI); solid horizontal line indicates average (ave); dotted horizontal line indicates median.

Fig. 4 .
Fig. 4. Time series of total n-alkane concentrations measured at Fukuoka City and Fukue Island.

Fig. 6 .
Fig. 6.Backward air mass trajectories from the FC and FI sites calculated for (a) 500 m in spring and winter, 2010, (b) 500 m in summer, 2011, (c) 1,000 m in spring and winter, 2010, (d) 1,000 m in summer, 2011, (e) 1,500 m in spring and winter, 2010, and (f) 1,500 m in summer, 2011; black curves indicate trajectories toward the FC site, while red curves indicate trajectories toward the FI site.

Table 2 .
Seasonal change in PAH concentration distribution.

Table 3 .
Seasonal change in n-alkane concentration distribution.