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Temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea
Atmospheric Environment 36 (2002) 5491–5500
Temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea Soo Ya Bae, Seung Muk Yi1, Yong Pyo Kim* Department of Environmental Science & Engineering, Ewha Womans University, 11-1 daehyun-dong, seodaemun-gu, Seoul 120 750, South Korea Received 17 December 2001; received in revised form 29 March 2002; accepted 19 April 2002
Abstract The atmospheric particle size distributions between 0.1 and 100 mm in diameter and their dry deposition fluxes of polycyclic aromatic hydrocarbons (PAHs) were measured at four sites in the mid-part of Korea to characterize the spatial distribution, the PAHs levels and dry deposition. Samples were collected at Inchon, Seoul, Yangsuri, and Yangpyoung between 21 and 25 February, and between 12 and 16 May 2000. Ambient size distributions were measured with a cascade impactor and a coarse particles rotary impactor. Dry deposition fluxes of particles were measured with dry deposition plates. The total particulate PAHs concentrations are between 22.9 and 410 ng m3 ; with an average of 139 ng m3 : The total particulate PAHs dry deposition fluxes were between 10 and 24 mg m2 day1 in winter, and between 4.1 and 8:2 mg m2 day1 in spring. Both the ambient concentrations and dry deposition fluxes of PAHs in winter are higher than spring mainly due to higher fuel consumption. The ambient concentrations of PAHs in Inchon were the highest followed by Yangpyoung, Yangsuri, and Seoul. The PAHs concentrations and fluxes of Yangsuri and Yangpyoung, rural areas in Korea, are higher than the rural areas in USA. It suggests a serious PAHs pollution level of rural areas in Korea. Based on the PAHs individual compounds’ levels and size distributions, it was suggested that Yangpyoung and Yangsuri have local PAHs sources in addition to transport from urban areas. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Dry deposition flux; Particle size distribution; Spatial distribution; Emission sources of PAHs
1. Introduction Atmospheric deposition, which is commonly classified as either dry or wet, has received a great deal of attention over the past decade due to concerns about the effect of deposited material on the environment (Eisenreich and Strachan, 1992). Atmospheric deposition is an important mechanism controlling the fate of air-borne toxics and their transfer from the atmosphere to natural surfaces. *Corresponding author. Tel.: +822-3277-2832; fax: +8223277-3275. E-mail address: [email protected] (Y.P. Kim). 1 Present address: Graduate School of Public Health, Seoul National University, Korea.
Polycyclic aromatic hydrocarbons (PAHs) are formed primarily during incomplete combustion of fossil fuels and wood. Major sources of PAHs include residential heating, open burning, coke and aluminum production, and motor vehicle exhaust (Finalyson-Pitts and Pitts, 1986). Atmosphere is a major pathway for the transport and deposition of PAHs. Several PAHs are known to be animal mutagens and/or carcinogens, and are potential humans carcinogens (IARC, 1983). Majority of PAHs (70–90%) are sorbed on suspended particles at ambient temperatures. Lighter PAHs with 2–3 benzene rings are mostly found in the gas phase while the heavier ones are mainly associated with air-borne particles. Moreover, PAHs are mostly sorbed on small inhalable particles with a high concentration on air-borne particles of submicron diameter (Vaeck and Cauwenberghe, 1978;
1352-2310/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 2 ) 0 0 6 6 6 - 0
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Nicolaou et al., 1984), which can be deposited in the respiratory tract, hence increasing the potential health effects. In this work, measurements of the size distributions between 0.1 and 100 mm in diameter and dry deposition fluxes of particulate PAHs at four sites, Korea in February and May 2000 were reported. The objective of this study is to understand the characteristics of temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea.
2. Experimental section 2.1. Sampling period and location Dry deposition fluxes and ambient size distributions were measured from 21 to 25 February and 12 to 16 May 2000 at four sites. During each period, the deposition plate was exposed for 4 days at each site. Samples were taken in Seoul, Inchon, Yangsuri, and Yangpyoung as shown in Fig. 1 during the periods of no rain. The ambient particle size distribution was measured with a cascade impactor and a coarse particle rotary impactor (CPRI). Dry deposition fluxes were continuously measured for 4 days during each sampling period and atmospheric size distributions were measured for 1 day except in Seoul. In Seoul, atmospheric size distributions were measured for 4 days during each sampling period. Sampling conditions are summarized in Table 1. Seoul (SE) is the largest city in Korea with 10 million inhabitants and 2.5 million vehicles. In Seoul, the site is
45N N
situated in Asan hall, Ewha Womans University. Samples were collected on a 3 m-high platform on the roof of Asan hall, a five-story 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. Inchon (IC) is the fourth largest city in Korea with 2.5 million inhabitants. Inchon is an industrial city with a harbor, a still work, and other various industrial activities. In Inchon, samples were collected on a 2:5 m-high platform on the roof of Inchon City hall. Since the City hall is located in the center of the city, traffic was heavy. In Yangsuri (YS), samples were collected on the roof of a two-story farmhouse separated from a road by about 200 m: Yangsuri is a popular outing place and traffic was heavy around the site. The average numbers of vehicles passing through the road per day were 26,644 and 36,653 for 1999 and 2000, respectively (Statistical yearbook, 1999, 2000). In Yangpyoung (YP), the site is surrounded with fields and farmhouses. Samples were measured on the roof of a two-story building separated 600 m from a road. During the planning stage, Inchon and Seoul were considered as major emission source areas of PAHs while Yangpyoung and Yangsuri were considered as rural background areas. 2.2. Dry deposition flux measurement Dry deposition fluxes were measured by using dry deposition plates with a sharp leading edge mounted on a wind vane. It was made of poly-vinyl chloride and its dimensions were 21:5 cm long, 7:6 cm wide, and 0:65 cm thick with a sharp leading edge ðo101Þ that was pointed into the wind by a wind vane. Each of the three plates was covered with four Mylar strips (7:6 cm 2:5 cm). These were coated with approximately 5 mg of Apezion L grease (thickness B5 mm) and used as collection surface on the top of the plate. This type of deposition plate with greased strip has been extensively used as a surrogate surface to directly assess deposited materials, for example (Yi et al., 1997). 2.3. Ambient particle size distribution measurements
40N SE, YS, YP IC
CHINA
KOREA
35N
JAPAN
30N 115E
120E
125E
130E
135E
Fig. 1. Location of the sampling sites. IC: Inchon, SE: Seoul, YS: Yangsuri, YP: Yangpyoung.
Atmospheric particles were measured with both a cascade impactor and a CPRI. It was calibrated with the unit density spherical particles so that all particles collected are sized aerodynamically equivalent to the reference particles. The cascade impactor separates particles into the following size ranges: 9–5.8, 5.8–3.3, 3.3–2.1, 2.1–1.1, 1.1–0.65, 0.65–0.43, and o0:43 mm: The medium used was Mylar coated with Apezion L grease to minimize particle bounce. The CPRI is a multistage rotary inertial impactor that collects large particles. It collects particles using simultaneously rotating four rectangular collectors (stage) of different dimensions through the air (Holsen
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Table 1 Summary of the sampling conditions Period
Winter
Spring
Site
2/22 25 SE
2/21 24 IC
2/22 25 YS
2/22 25 YP
5/12 15 SE
5/12 15 IC
5/12 14 YS
5/14 16 YP
Sampling time (min)
Plate cascade impactor CPRI
2119 2184 476
1763 389 195
1640 393 240
1665 358 120
1715 1753 476
1434 311 195
1561 385 240
630 405 240
Met. conditions
WS ðm s1 Þ
3.5
4.7
1.5
1.8
2.5
3.5
1.5
1.1
NW+
WN
WN
WS W+
W+W WD (%)
Temp. (K) RH (%)
WS
W+W
W+
SSE+ W+S
SW+ NW (77)
274.3 44.1
W +NW (72) 275.0 45.0
SW+ NW (64) 274.9 46.8
W+ NW (67) 274.8 43.8
S+ S+
W+ WNW (49) 293.7 52
W (55) 292.3 61.4
SSW (43) 293.6 49.7
SSE (63)
295.3 49.1
SE: Seoul, IC: Inchon, YS: Yangsuri, YP: Yangpyoung, WS: Wind speed, WD: Wind direction, RH: Relative humidity.
and Noll, 1992). The stages are covered with Mylar strips coated with Apezion L grease. Total collection areas were 1:2; 3:1; 10:3; and 10:3 cm2 for stages A–D, respectively. In this study, the CPRI was operated at 320 rpm; which produced theoretical aerodynamic (particle density of 1 g cm3 ) cut diameters of 4:5; 8:1; 17:4; and 25:8 mm for stages A–D, respectively. 2.4. Analysis Details of the analytical procedure are given in Odabasi (1998). The samples were spiked with PAHs surrogate standards prior to extraction in order to determine analytical recovery efficiency. Greased strips were soxhlet extracted with a mixture of dichloromethane (DCM): petroleum ether (PE) (20:80) for 24 h that were then concentrated by using the Kuderna– Danish (K–D) evaporator to approximately 5 ml: Solvent was exchanged into hexane by addition of 15 ml hexane and evaporating the mixture to 5 ml: Again 15 ml of hexane was added and it was blown down to 2 ml using a gentle stream of nitrogen. Samples were cleaned up and fractionated on an alumina–silicic acid column. The column was packed by adding deactivated silicic acid, alumina, and 2 cm of Na2 SO4 in DCM-slurry in the given order. The sample in 2 ml hexane was added into the column with a 2 ml rinse of PE and eluent was collected in a vial at a rate of two drops per second. After letting the sample pass through
the column, 25 ml DCM was added and eluent collected in the same vial. The solvent was exchanged into hexane, and the final sample volume was adjusted to 1 ml by nitrogen blow-down and analyzed without further cleanup. PAHs were measured by using an HP GC/MS system consisting of an HP Model 6890 gas chromatograph and an HP Model 5974 mass selective detector (MSD). A DB-5 column (60 m; 0:25 mm i.d.) was used for PAHs analysis. The GC/MS system condition and operational parameters were quoted from the analyzed conditions used at NOAA (NOAA, 1993). Recoveries of PAHs internal standards were 29:97 13:8% ðn ¼ 40Þ for naphthalene-d8, 52:674:84% ðn ¼ 40Þ for acenaphthalene-d10, 63:777:32% ðn ¼ 40Þ for phenanthrene-d10, 68:275:61% ðn ¼ 40Þ for chrysened12, 56:875:05% ðn ¼ 40Þ for perylene-d12 for all sample matrices. The recovery of napthalene-d8 was very low so naphthalene was identified but not quantified. The analytical method used for samples was tested by analyzing aliquots of NIST standard Urban Dust Reference Material (SRM-1649a). Concentrations of PAHs in SRM-1649a, as the percent of NIST certified values were certified value 720:1%: Method of detection limits (MDLs) was ranged below 0:12 ng m3 : Blanks were analyzed at every extraction but tendency was not found. Blank levels were low on the average.
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3. Results and discussion 3.1. Particulate PAHs concentrations The total particulate PAHs concentrations are between 22.9 and 410 ng m3 as shown in Table 2 with the average value of 139 ng m3 : The total particulate PAHs concentrations show a tendency that PAHs concentrations measured in winter are higher than those measured in spring. There are two possible reasons for the higher particulate PAHs concentration in winter than in spring: temperature dependence of gas/aerosol partitioning of PAHs and higher emissions during winter. Since the average temperatures during the winter sampling period were lower than in spring by about
20 K as shown in Table 1, preferential sorption of PAHs onto particles in winter should contribute to the higher PAHs concentrations in winter to some extent. Since the major source of ambient PAHs is incomplete combustion of fossil fuels, higher concentrations of the total PAHs in winter can be also closely related with the larger amount of fossil fuel usage in winter for heating than in spring (Baek and Choi, 1996). To understand the relative importance of temperature and emission effects, the concentrations of the PAHs compounds containing fine or more fused rings were studied. PAHs observed in the atmosphere range from bicyclic species, present largely in the gas phase, to compounds containing five or more fused rings that are present in the particulate phase. Benzo(a)pyrene, Indeno(1,2,3-cd)pyrene,
Table 2 Size distributions of the total particulate PAHs concentrations measured at four sites, Korea in February and May 2000 Season Winter
Spring
Period PAHs concentrations (ng m3 )
2/22 25
2/21 24
2/22 25
2/22 25
5/12 15
5/12 15
5/12 14
5/14 16
IC
YS
YP
SE
IC
YS
YP
Site SE Small particle
Back-up filter
o0.43
7th Stage
0.43 B0.65 0.65 B2.1 2.1 B3.3 3.3 B5.8 5.8 B9.0 o9.0
6th Stage 4th Stage 3rd Stage 1st Stage Total Large particles
B Stage C Stage D Stage Total
Total PAHs Small particle fraction (%) Large particle fraction (%)
8.1 B17.4 17.4 B25.8 25.8 B100 8.1 B100
18.7
61.9
23.6
28.3
3.60
18.2
8.49
20.1
65.1
18.8
17.6
4.11
16.3
18.7
59.4
21.8
55.4
3.37
18.4
8.37
14.7
15.4
55.5
16.3
25.0
3.65
15.9
9.42
13.3
17.1
64.5
17.8
15.6
3.48
18.3
9.91
12.7
16.4 106
94.9 401
15.0 113
42.7 185
3.19 21.4
14.0 101
15.6
16.2 68.0
7.77
15.5
20.3 84.3
1.42
6.05
4.57
7.13
0.64
1.01
2.21
2.88
0.30
1.20
0.39
1.13
0.51
1.45
2.09
1.97
0.37
1.19
0.72
2.20
0.31
1.53
1.76
2.76
2.09
8.44
5.68
10.46
1.46
3.99
6.06
7.61
109
410
119
195
22.9
105
74.1
91.8
98.1
97.9
95.2
94.6
93.6
96.2
91.8
91.7
1.9
2.1
4.8
5.4
6.4
3.8
8.2
8.3
Small particles (Dp p9 mm), large particles (Dp > 9 mm), unit of stage cut size: mm:
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concentration than large particles. It has been known that when PAHs compounds emitted in the gaseous phases were condensed into particle phase, PAHs compounds were mostly distributed to small particles. Then, the PAHs compounds with high vapor pressures or low molecular weights evaporate and recondense onto the large particles (Allen et al., 1996). Therefore, the results also suggest that Inchon and Yangpyoung have emission sources near the sites. The ratios of PAHs in large particle to total PAHs concentrations in Yangsuri and Yangpyoung as shown in Table 3 are, however, higher than in Inchon and Seoul. If sources are near, majority of PAHs should be in the small particles as explained before. This suggests that in Yangsuri and Yangpyoung, some fraction of PAHs, especially, PAHs in large particles might be transported from urban areas. The results of this study are compared with other studied in USA in Table 4. In USA, the PAHs concentrations in urban areas (Boston, Chicago, and Houston) are higher than those in rural areas (Lake Guardian and South Haven) by a fraction of 10 or larger, as shown in Table 4. Higher ambient PAHs concentrations in urban areas are likely due to higher emissions from local sources. The PAHs concentrations of Inchon and Seoul in winter, 410 and 109 ng m3 ; respectively, were comparable to or lower than those of Boston, Chicago, and Houston, USA. However, the PAHs concentrations of Yangsuri and Yangpyoung are 3–5 times higher than Lake Guardian and South Haven, typical rural areas in USA. This shows serious PAHs pollution levels in rural areas of Korea. Therefore, Yangsuri and Yangpyoung may have local emission sources in addition to the effects of transport from outside. It is interesting to note that the PAHs level in Seoul is rather low. The sampling site at Seoul is located in a university campus with low fossil fuel combustion. This might explain the low PAHs levels.
Dibenzo(a,h)anthracene, and Benzo(g,h,i)pyrene, which contained five fused rings, are predominantly present in the particulate phase. The concentrations of these high molecular weight compounds in winter are far higher than in spring at all sites. For example, in Seoul the total concentration of these was 2:12 ng m3 in winter while in spring 0:28 ng m3 : The concentrations in winter are about 10 times higher than those in spring. It shows that the higher concentrations of PAHs in winter than spring are mainly due to higher emission while the temperature effect cannot be neglected. In both seasons, the total PAHs concentrations at Inchon were the highest followed by Yangpyoung, Yangsuri, and Seoul. This trend is contrary to the original expectation that the total PAHs concentrations at Inchon and Seoul be higher than those at Yangsuri and Yangpyoung because Inchon and Seoul have major emission sources and Yangsuri and Yangpyoung are rural areas. For all the samples, more than 60 wt% of PAHs were in particles with diameter less than 3 mm and more than 90 wt% of PAHs were in the particles with diameter less than 9 mm as shown in Table 2. It can be explained by the fact that semivolatile organic compounds (SOCs) such as PAHs are mainly distributed at fine particles (Pankow et al., 1997). Table 3 shows the ratios of the PAHs concentration to the mass concentration for small (Dp p9 mm) and large (Dp p9 mm) particles. The mass size distribution was not quantified in Yangsuri during May, only PAHs size distribution was quantified. For both size ranges, the PAHs to mass concentration ratios in winter were higher than those in spring, especially at Inchon and Yangpyoung. In addition, the ratios at Inchon and Yangpyoung were 2–5 times higher than the other two sites in winter. This suggests that Inchon and Yangpyoung have emission sources near to the sites. For all the samples, small particles contain more PAHs per unit mass
Table 3 Ratio of PAHs to the particle mass concentrations of small and large particles measured at four sites, Korea in winter and spring, 2000 (mg PAHs g1 particle1 ) Winter
Spring
SE
IC
YS
YP
Small particle Large particle Total
64.5 1.26 65.8
119 2.56 122
36.2 1.82 38.0
100 5.69 106
Ratio of PAHs in small particles to PAHs in large particles
46.4
51.0
20.0
17.7
Small particles (Dp p9 mm), large particles (Dp > 9 mmÞ:
SE 1.07 0.073 1.14 25.3
IC 20.8 0.819 21.6 14.6
YS 4.43 0.395 4.83 11.2
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3.2. Dry deposition fluxes
fluxes in winter were higher than in spring at all sites. The dry deposition fluxes of Inchon were the highest among the four sites during both seasons, and the other three sites have statistically comparable fluxes. As mentioned earlier, the sites were chosen under the assumption that Seoul and Inchon were main emission areas of PAHs. But the flux results indicate that in addition to the ambient PAHs levels, Yangsuri and Yangpyoung might have extra emission sources. The results of this study are compared with those of another study in USA, as shown in Table 5. The dry deposition fluxes of PAHs in Inchon and Seoul are lower than that in Chicago, USA except Inchon winter. However, the dry deposition fluxes of PAHs in Yangsuri and Yangpyoung are 30 times higher than South Haven and Sleeping Bear Dunes, rural areas in USA. It also shows serious PAHs pollution levels in rural areas of Korea. Usually, dry deposition flux is described as the product of the dry deposition velocity and the ambient concentration. The factors affecting dry deposition velocity are wind speed, atmospheric stability, particle density, and particle size (Sehmel, 1973). The wind speeds and ambient PAHs concentration of Inchon (4:7 m s1 ) were higher than other sites (3:5 m s1 in Seoul, 1:5 m s1 in Yangsuri, and 1:8 m s1 in Yangpyoung) based on the meteorological data (Korea Meteorological Administration, private communication). Thus, dry deposition flux of Inchon is the highest among the four sampling sites. The atmospheric PAHs concentrations of Yangsuri and Yangpyoung are higher
The total particulate PAHs dry deposition fluxes were between 10 and 24 mg m2 day1 in winter, and between 4.1 and 8:2 mg m2 day1 in spring as shown in Fig. 2. During spring, the flux measurement at Yangpyoung was not carried out due to a sampler problem. Same as the ambient PAHs concentrations, the dry deposition
Table 4 Comparison of ambient levels of PAHs with other measurement results Location
Total PAHs ðng m3 Þ
Reference
Seoul, Korea Inchon, Korea Yangsuri, Korea Yangpyoung, Korea
109/22.9 410/101 119/74.1 195
This This This This
Boston, USA Chicago, USA
194 442
Chicago, USA
428
Houston, USA Lake Gaurdian, USA South Haven, USA
119 22
Lewis et al. (1991), summer Cotham and Bidleman (1995), winter Odabasi et al. (1999), summer-fall Lewis et al. (1991), summer Simcik et al. (1997)
21
Simcik et al. (1997)
study, study, study, study,
winter/spring winter/spring winter/spring winter
Flux of particulate PAHs (µg m-2 day-1)
50 winter spring 40
30
20
10
0 Inchon
Seoul
Yangsuri
Yangpyoung
Sampling site Fig. 2. Histogram of the particulate PAHs fluxes measured with dry deposition plate: (a) Inchon and (b) Yangsuri.
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Table 5 Comparison of the dry deposition PAHs fluxes measurement Location
Season
Mass flux ðmg m2 day1 Þ
PAHs flux (mg m2 day1 Þ
Reference
Seoul, Korea
Winter Spring Winter Spring Winter Spring Winter
340 360 97 120 180 220 32
12 5.5 24 8.2 10 4.1 11
This study
This study This study
18.0 0.7 0.2 0.3
Franz Franz Franz Franz
Inchon, Korea Yangsuri, Korea Yangpyoung, Korea Chicago, USA Over-Lake, USA South Haven, MI, USA Sleeping Bear Dunes, MI, USA
— — — —
65 12 10 3.6
that those of Seoul. But the PAHs fluxes in Seoul, Yangsuri, and Yangpyoung are similar. The wind speeds, an important factor affecting dry deposition velocity, in Seoul were the highest among three sites. Therefore, although the ambient PAHs concentrations were higher at Yangsuri and Yangpyoung than at Seoul, the dry deposition fluxes of PAHs were statistically similar at three sites. This shows that wind speeds are an important factor on dry deposition velocity and, thus, dry deposition flux. 3.3. Characteristics of individual PAH compounds In Sections 3.1 and 3.2, it was shown that Yangsuri and Yangpyoung have local sources of PAHs in addition to the transport from outside. To further understand the difference of the PAHs levels between urban and rural areas, the ambient concentrations of individual PAH compounds at each site are studied and those in Inchon and Yangsuri are shown in Fig. 3. In Inchon, phenanthrene (PHE) was the most abundant compound. Also, the concentrations of other low molecular weight PAHs in Inchon were also higher than Yangsuri and Yangpyoung. The concentrations of high molecular weight PAHs in Inchon were similar to these at other sites. This suggests that in Inchon, there are direct emission sources of PAHs. Though not shown, the PAHs compounds’ profile in Seoul is similar to that in Inchon and, thus, it is likely that they might have common emission sources. Yangsuri and Yangpyoung have different PAHs profiles from Inchon and Seoul as shown in Fig. 3. The concentrations of high molecular weight PAHs compounds in Inchon and Seoul were higher than in Yangsuri and Yangpyoung. For example, the ambient concentrations of Benzo(a)pyrene (BaP) in Inchon and Seoul were 0:73 and 0:61 ng m3 ; respec-
This study
et et et et
al. al. al. al.
(1998) (1998) (1998) (1998)
tively, while the concentrations were 0:17 and 0:53 ng m3 at Yangsuri and Yangpyoung, respectively, in winter. In spring the concentrations of BaP in Yangsuri and Yangpyoung were below the detection limits while those at Inchon and Seoul were 0.18 and 0:079 ng m3 ; respectively. Fig. 4 shows individual PAH compounds levels in the deposited particles in Inchon and Yangsuri. Inchon and Seoul have similar PAHs profiles in the deposited particles and thus, as mentioned earlier, two areas might have common emission sources as shown in Fig. 4. For instance, the flux levels increase with the increase of molecular weight until PHE in Inchon and Seoul except acenaphthalene (ACE). The value of ACE is larger than acenaphthene (ACT) in Inchon and Seoul. Since the different PAHs profiles indicate different emission sources (Daisey et al., 1995; Lee et al., 1976), it suggests a possibility that there are local emission sources of PAHs in Yangsuri and Yangpyoung. One possible source of PAHs in the rural areas is open burning of agricultural and other wastes. It has been reported that the PAHs profile depends on the type of emission sources. For example, PHE, FL, and PY are typical diesel vehicles markers and indeno(1,2,3-cd)pyrene (IcdP) and benzo(g,h,i)pyrene (BghiP) are typical gasoline vehicle markers (Harrison et al., 1996). Also, Benzo(a)pyrene (BaP) is a typical marker for coke oven in a steel work (Smith, 1984). As shown earlier, the ambient concentrations of BaP in Inchon and Seoul in winter were higher than that in Yangsuri and Yangpyoung. This suggests that BaP emitted in a steel work in Inchon might affect both Inchon and Seoul sites. In Inchon, the ambient concentration of PHE was 3–4 times higher than other sites. In Seoul, the ambient concentrations of all PAHs compound are low in winter. But the ambient
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PAHs concentration (ng m-3)
200 small particle (winter) large particle (winter) small particle (spring) large particle (spring)
150
100
50
0 ACE ACT FLN PHE ANT FL PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
(a) Inchon
PAHs concentration (ng m-3)
100 small particle (winter) large particle (winter) small particle (spring) large particle (spring)
75
50
25
0 ACE ACT FLN PHE ANT FL (b) Yangsuri
PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
Fig. 3. Ambient PAHs concentration measured by cascade impactor for small particles and by CPRI for large particles at: (a) Inchon and (b) Yangsuri.
concentrations of IcdP and BghiP, gasoline vehicle markers, were higher than those in Inchon. This shows that in Seoul and Inchon, vehicles were the main emission sources of PAHs; but in Seoul, effects from gasoline vehicles were more prominent. In Yangsuri and Yangpyoung major emission sources were not identified. But since the ambient concentrations of PAHs at both sites were higher than Seoul and the BaP concentrations were lower than Inchon and Seoul it is likely that there are rather strong local emission sources of PAHs in Yangsuri and Yangpyoung.
4. Summary PAHs are a class of persistent organic pollutants (POPs). In Korea, spatial distribution of PAHs has not been reported yet. To control the ambient PAHs levels, it is essential to study temporal and spatial variations of PAHs and their dry deposition fluxes. The atmospheric particle mass size distributions between 0.1 and 100 mm in diameter and their deposition fluxes of PAHs were measured at four sites in the midpart of Korea in February and May 2000 to characterize the spatial and temporal variations distribution of
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Flux of particulate PAHs (µg m-2 day-1)
15 winter spring
10
5
0 (a) Inchon
ACE ACT FLN PHE ANT FL PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
Flux of particulate PAHs (µg m-2 day-1)
15 winter spring
5
0 (b) Yangsuri
ACE ACT FLN PHE ANT FL PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
Fig. 4. The particulate PAHs compounds fluxes measured with dry deposition plate in: (a) Inchon and (b) Yangsuri.
particulate dry deposition of PAHs. Samples were collected at two urban areas: Inchon, Seoul; and two rural areas; Yangsuri and Yangpyoung between 21 and 25 February, and between 12 and 16 May 2000. The total particulate PAHs concentrations are between 22.9 and 410 ng m3 with an average of 139 ng m3 : The total particulate PAHs dry deposition fluxes are between 10 and 24 mg m2 day1 in winter, and between 4.1 and 8:2 mg m2 day1 in spring. At all sites, the ambient concentrations of PAHs and dry deposition fluxes in winter were higher than spring mainly due to higher emissions of PAHs from fuel combustion. The ambient concentrations of PAHs in
Inchon were the highest followed by Yangpyoung, Yangsuri, and Seoul. The dry deposition fluxes of Inchon were also the highest and those at other sites were statistically comparable. The fractions of PAHs in small particles (Dp p9 mm) in Inchon and Yangpyoung were higher than other sites. Further, the ambient concentrations and dry deposition fluxes of PAHs in Inchon and Seoul were comparable to lower than those in urban areas, USA, but those in Yangpyoung and Yangsuri were higher than those in rural areas, USA. Based on these observations, it was suggested that the PAHs levels in Yangpyoung and Yangsuri are affected by both local emission source and the transport from
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outside. However, in Yangpyoung and Yangsuri, no specific emission source was identified. It is recommended that to further identify and characterize high PAHs levels in rural areas of Korea, further source identification studies are needed in Korea.
Acknowledgements This paper was written with support from the Climate Environment System Research Center, an SRC program funded by the Korea Science and Engineering Foundation, the Brain Korea 21 Program, and the Ministry of Environment, Korea.
References Allen, J.O., Dookeran, N.M., Smith, K.A., Sarofim, A.D., Taghizadeh, K., Lafleur, A.L., 1996. Measurement of polycyclic aromatic hydrocarbons associated with sizesegregated atmospheric aerosols in Massachusetts. Environmental Science and Technology 30, 1023–1031. Baek, S.O., Choi, J.S., 1996. Occurrence and behaviour of polycyclic aromatic hydrocarbons in the ambient air (I) (in Korean). Journal of Korean Society for Atmospheric Environment 18, 465–480. Cotham, W.E., Bidleman, T.F., 1995. Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls in air at an urban and a rural site near Lake Michigan. Environmental Science and Technology 29, 2782–2789. Daisey, J.M., Cheney, J.L., Lioy, P.J., 1995. Profiles of organic particulate emissions from air pollution sources: status and needs for receptor source apportionment modeling. Journal of the Air Pollution Control Association 36, 17–33. Eisenreich, S.J., Strachan, W.M.J., 1992. Estimating atmospheric deposition of toxic substances to great lakes. Paper presented in the 1992 Workshop Sponsored by the Great Lakes protection Fund and Environment Canada, Ont., Canada. Finalyson-Pitts, B.J., Pitts Jr., J.N., 1986. Atmospheric Chemistry: Fundamentals and Experimental Techniques. Wiley, New York, USA. Harrison, R.M., Smith, D.T.J., Luhana, L., 1996. Source apportionment of atmospheric polycyclic aromatic hydrocarbons collected from an urban location in Birmingham, UK. Environmental Science and Technology 30, 825–832. Holsen, T.M., Noll, K.E., 1992. Dry deposition of atmospheric particles: application of current models to ambient data. Environmental Science and Technology 26, 1807–1815.
IARC, 1983. Polynuclear aromatic compounds, Part 1: chemical, environmental and experimental data. 32, Lyon, France, IARC Working Group on the Evaluation of the Carcinogenic Risk of Chemicals to Humans, France. Lee, M.L., Novotny, M., Bartle, K.D., 1976. Gas chromatography/mass spectrometric and nuclear magnetic resonance determination of polynuclear aromatic hydrocarbons in airborne particulates. Analyze Chemistry 48, 1566–1572. Lewis, R.G., Kelly, T.J., Chuang, J.C., Callahan, P.J., Coutart, R.W., 1991. Phase distributions of airborne polycyclic aromatic hydrocarbons in two U.S. cities. Proceedings of the 9th World Clean Air Congress & Exhibition, Montreal, Canada. Nicolaou, K., Masclet, P., Mouvier, G., 1984. Sources and chemical reactivity of polynuclear aromatic hydrocarbons in the atmosphere—a critical review. The Science of the Total Environment 32, 103–132. NOAA, 1993. Sampling and analytical methods of the National Status and Trends Program-National benthic surveillance and mussel watch projects, 1984–1992. NOAA Technical Memorandum NOS ORCA 71, Vol. II, pp. 41–42. Odabasi, M., 1998. Measurement of PAH dry deposition and air–water exchange with the water surface sampler. Ph.D. Thesis, Illinois Institute of Technology, Chicago, IL, USA. Odabasi, M., Bardar, N., Sofuoglu, A., Tasdemir, Y., Holsen, T.M., 1999. Polycyclic aromatic hydrocarbons (PAHs) in Chicago air. The Science of the Total Environment 227, 57–67. Pankow, J.F., Liang, C., Odum, J.R., Seinfeld, J.H., 1997. Gas/ particle partitioning of semivolatile organic compounds to model inorganic, organic, and ambient smog aerosols. Environmental Science and Technology 28, 2001–2007. Sehmel, G.A., 1973. Particle eddy diffusivities and deposition velocities for isothermal flow and smooth surfaces. Aerosol Science and Technology 4, 125–138. Simcik, M.F., Zhang, H., Eisenreich, S.J., Franz, T.P., 1997. Urban contamination of the Chicago/Coastal Lake Michigan atmosphere by PCBs and PAHs during AEOLOS. Environmental Science and Technology 31, 2141–2147. Smith, I.M., 1984. PAH from Coal Utilization-Emissions and Effects. IEA Coal Research, USA. Statistical yearbook, 1999. The Ministry of Construction and Transportation, Korea. Statistical yearbook, 2000. The Ministry of Construction and Transportation, Korea. Vaeck, L.V., Cauwenberghe, K.V., 1978. Cascade impactor measurements of the size distribution of the major classes of organic pollutants in atmospheric particulate matter. Atmospheric Environment 12, 2229–2239. Yi, S.M., Holsen, T.M., Zhu, X., Noll, K.E., 1997. Sulfate dry deposition measured with a water surface sampler: a comparison to modeled results. Journal of Geophysics Research 102, 19695–19705.
Temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea Soo Ya Bae, Seung Muk Yi1, Yong Pyo Kim* Department of Environmental Science & Engineering, Ewha Womans University, 11-1 daehyun-dong, seodaemun-gu, Seoul 120 750, South Korea Received 17 December 2001; received in revised form 29 March 2002; accepted 19 April 2002
Abstract The atmospheric particle size distributions between 0.1 and 100 mm in diameter and their dry deposition fluxes of polycyclic aromatic hydrocarbons (PAHs) were measured at four sites in the mid-part of Korea to characterize the spatial distribution, the PAHs levels and dry deposition. Samples were collected at Inchon, Seoul, Yangsuri, and Yangpyoung between 21 and 25 February, and between 12 and 16 May 2000. Ambient size distributions were measured with a cascade impactor and a coarse particles rotary impactor. Dry deposition fluxes of particles were measured with dry deposition plates. The total particulate PAHs concentrations are between 22.9 and 410 ng m3 ; with an average of 139 ng m3 : The total particulate PAHs dry deposition fluxes were between 10 and 24 mg m2 day1 in winter, and between 4.1 and 8:2 mg m2 day1 in spring. Both the ambient concentrations and dry deposition fluxes of PAHs in winter are higher than spring mainly due to higher fuel consumption. The ambient concentrations of PAHs in Inchon were the highest followed by Yangpyoung, Yangsuri, and Seoul. The PAHs concentrations and fluxes of Yangsuri and Yangpyoung, rural areas in Korea, are higher than the rural areas in USA. It suggests a serious PAHs pollution level of rural areas in Korea. Based on the PAHs individual compounds’ levels and size distributions, it was suggested that Yangpyoung and Yangsuri have local PAHs sources in addition to transport from urban areas. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Dry deposition flux; Particle size distribution; Spatial distribution; Emission sources of PAHs
1. Introduction Atmospheric deposition, which is commonly classified as either dry or wet, has received a great deal of attention over the past decade due to concerns about the effect of deposited material on the environment (Eisenreich and Strachan, 1992). Atmospheric deposition is an important mechanism controlling the fate of air-borne toxics and their transfer from the atmosphere to natural surfaces. *Corresponding author. Tel.: +822-3277-2832; fax: +8223277-3275. E-mail address: [email protected] (Y.P. Kim). 1 Present address: Graduate School of Public Health, Seoul National University, Korea.
Polycyclic aromatic hydrocarbons (PAHs) are formed primarily during incomplete combustion of fossil fuels and wood. Major sources of PAHs include residential heating, open burning, coke and aluminum production, and motor vehicle exhaust (Finalyson-Pitts and Pitts, 1986). Atmosphere is a major pathway for the transport and deposition of PAHs. Several PAHs are known to be animal mutagens and/or carcinogens, and are potential humans carcinogens (IARC, 1983). Majority of PAHs (70–90%) are sorbed on suspended particles at ambient temperatures. Lighter PAHs with 2–3 benzene rings are mostly found in the gas phase while the heavier ones are mainly associated with air-borne particles. Moreover, PAHs are mostly sorbed on small inhalable particles with a high concentration on air-borne particles of submicron diameter (Vaeck and Cauwenberghe, 1978;
1352-2310/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 2 ) 0 0 6 6 6 - 0
S.Y. Bae et al. / Atmospheric Environment 36 (2002) 5491–5500
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Nicolaou et al., 1984), which can be deposited in the respiratory tract, hence increasing the potential health effects. In this work, measurements of the size distributions between 0.1 and 100 mm in diameter and dry deposition fluxes of particulate PAHs at four sites, Korea in February and May 2000 were reported. The objective of this study is to understand the characteristics of temporal and spatial variations of the particle size distribution of PAHs and their dry deposition fluxes in Korea.
2. Experimental section 2.1. Sampling period and location Dry deposition fluxes and ambient size distributions were measured from 21 to 25 February and 12 to 16 May 2000 at four sites. During each period, the deposition plate was exposed for 4 days at each site. Samples were taken in Seoul, Inchon, Yangsuri, and Yangpyoung as shown in Fig. 1 during the periods of no rain. The ambient particle size distribution was measured with a cascade impactor and a coarse particle rotary impactor (CPRI). Dry deposition fluxes were continuously measured for 4 days during each sampling period and atmospheric size distributions were measured for 1 day except in Seoul. In Seoul, atmospheric size distributions were measured for 4 days during each sampling period. Sampling conditions are summarized in Table 1. Seoul (SE) is the largest city in Korea with 10 million inhabitants and 2.5 million vehicles. In Seoul, the site is
45N N
situated in Asan hall, Ewha Womans University. Samples were collected on a 3 m-high platform on the roof of Asan hall, a five-story 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. Inchon (IC) is the fourth largest city in Korea with 2.5 million inhabitants. Inchon is an industrial city with a harbor, a still work, and other various industrial activities. In Inchon, samples were collected on a 2:5 m-high platform on the roof of Inchon City hall. Since the City hall is located in the center of the city, traffic was heavy. In Yangsuri (YS), samples were collected on the roof of a two-story farmhouse separated from a road by about 200 m: Yangsuri is a popular outing place and traffic was heavy around the site. The average numbers of vehicles passing through the road per day were 26,644 and 36,653 for 1999 and 2000, respectively (Statistical yearbook, 1999, 2000). In Yangpyoung (YP), the site is surrounded with fields and farmhouses. Samples were measured on the roof of a two-story building separated 600 m from a road. During the planning stage, Inchon and Seoul were considered as major emission source areas of PAHs while Yangpyoung and Yangsuri were considered as rural background areas. 2.2. Dry deposition flux measurement Dry deposition fluxes were measured by using dry deposition plates with a sharp leading edge mounted on a wind vane. It was made of poly-vinyl chloride and its dimensions were 21:5 cm long, 7:6 cm wide, and 0:65 cm thick with a sharp leading edge ðo101Þ that was pointed into the wind by a wind vane. Each of the three plates was covered with four Mylar strips (7:6 cm 2:5 cm). These were coated with approximately 5 mg of Apezion L grease (thickness B5 mm) and used as collection surface on the top of the plate. This type of deposition plate with greased strip has been extensively used as a surrogate surface to directly assess deposited materials, for example (Yi et al., 1997). 2.3. Ambient particle size distribution measurements
40N SE, YS, YP IC
CHINA
KOREA
35N
JAPAN
30N 115E
120E
125E
130E
135E
Fig. 1. Location of the sampling sites. IC: Inchon, SE: Seoul, YS: Yangsuri, YP: Yangpyoung.
Atmospheric particles were measured with both a cascade impactor and a CPRI. It was calibrated with the unit density spherical particles so that all particles collected are sized aerodynamically equivalent to the reference particles. The cascade impactor separates particles into the following size ranges: 9–5.8, 5.8–3.3, 3.3–2.1, 2.1–1.1, 1.1–0.65, 0.65–0.43, and o0:43 mm: The medium used was Mylar coated with Apezion L grease to minimize particle bounce. The CPRI is a multistage rotary inertial impactor that collects large particles. It collects particles using simultaneously rotating four rectangular collectors (stage) of different dimensions through the air (Holsen
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Table 1 Summary of the sampling conditions Period
Winter
Spring
Site
2/22 25 SE
2/21 24 IC
2/22 25 YS
2/22 25 YP
5/12 15 SE
5/12 15 IC
5/12 14 YS
5/14 16 YP
Sampling time (min)
Plate cascade impactor CPRI
2119 2184 476
1763 389 195
1640 393 240
1665 358 120
1715 1753 476
1434 311 195
1561 385 240
630 405 240
Met. conditions
WS ðm s1 Þ
3.5
4.7
1.5
1.8
2.5
3.5
1.5
1.1
NW+
WN
WN
WS W+
W+W WD (%)
Temp. (K) RH (%)
WS
W+W
W+
SSE+ W+S
SW+ NW (77)
274.3 44.1
W +NW (72) 275.0 45.0
SW+ NW (64) 274.9 46.8
W+ NW (67) 274.8 43.8
S+ S+
W+ WNW (49) 293.7 52
W (55) 292.3 61.4
SSW (43) 293.6 49.7
SSE (63)
295.3 49.1
SE: Seoul, IC: Inchon, YS: Yangsuri, YP: Yangpyoung, WS: Wind speed, WD: Wind direction, RH: Relative humidity.
and Noll, 1992). The stages are covered with Mylar strips coated with Apezion L grease. Total collection areas were 1:2; 3:1; 10:3; and 10:3 cm2 for stages A–D, respectively. In this study, the CPRI was operated at 320 rpm; which produced theoretical aerodynamic (particle density of 1 g cm3 ) cut diameters of 4:5; 8:1; 17:4; and 25:8 mm for stages A–D, respectively. 2.4. Analysis Details of the analytical procedure are given in Odabasi (1998). The samples were spiked with PAHs surrogate standards prior to extraction in order to determine analytical recovery efficiency. Greased strips were soxhlet extracted with a mixture of dichloromethane (DCM): petroleum ether (PE) (20:80) for 24 h that were then concentrated by using the Kuderna– Danish (K–D) evaporator to approximately 5 ml: Solvent was exchanged into hexane by addition of 15 ml hexane and evaporating the mixture to 5 ml: Again 15 ml of hexane was added and it was blown down to 2 ml using a gentle stream of nitrogen. Samples were cleaned up and fractionated on an alumina–silicic acid column. The column was packed by adding deactivated silicic acid, alumina, and 2 cm of Na2 SO4 in DCM-slurry in the given order. The sample in 2 ml hexane was added into the column with a 2 ml rinse of PE and eluent was collected in a vial at a rate of two drops per second. After letting the sample pass through
the column, 25 ml DCM was added and eluent collected in the same vial. The solvent was exchanged into hexane, and the final sample volume was adjusted to 1 ml by nitrogen blow-down and analyzed without further cleanup. PAHs were measured by using an HP GC/MS system consisting of an HP Model 6890 gas chromatograph and an HP Model 5974 mass selective detector (MSD). A DB-5 column (60 m; 0:25 mm i.d.) was used for PAHs analysis. The GC/MS system condition and operational parameters were quoted from the analyzed conditions used at NOAA (NOAA, 1993). Recoveries of PAHs internal standards were 29:97 13:8% ðn ¼ 40Þ for naphthalene-d8, 52:674:84% ðn ¼ 40Þ for acenaphthalene-d10, 63:777:32% ðn ¼ 40Þ for phenanthrene-d10, 68:275:61% ðn ¼ 40Þ for chrysened12, 56:875:05% ðn ¼ 40Þ for perylene-d12 for all sample matrices. The recovery of napthalene-d8 was very low so naphthalene was identified but not quantified. The analytical method used for samples was tested by analyzing aliquots of NIST standard Urban Dust Reference Material (SRM-1649a). Concentrations of PAHs in SRM-1649a, as the percent of NIST certified values were certified value 720:1%: Method of detection limits (MDLs) was ranged below 0:12 ng m3 : Blanks were analyzed at every extraction but tendency was not found. Blank levels were low on the average.
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3. Results and discussion 3.1. Particulate PAHs concentrations The total particulate PAHs concentrations are between 22.9 and 410 ng m3 as shown in Table 2 with the average value of 139 ng m3 : The total particulate PAHs concentrations show a tendency that PAHs concentrations measured in winter are higher than those measured in spring. There are two possible reasons for the higher particulate PAHs concentration in winter than in spring: temperature dependence of gas/aerosol partitioning of PAHs and higher emissions during winter. Since the average temperatures during the winter sampling period were lower than in spring by about
20 K as shown in Table 1, preferential sorption of PAHs onto particles in winter should contribute to the higher PAHs concentrations in winter to some extent. Since the major source of ambient PAHs is incomplete combustion of fossil fuels, higher concentrations of the total PAHs in winter can be also closely related with the larger amount of fossil fuel usage in winter for heating than in spring (Baek and Choi, 1996). To understand the relative importance of temperature and emission effects, the concentrations of the PAHs compounds containing fine or more fused rings were studied. PAHs observed in the atmosphere range from bicyclic species, present largely in the gas phase, to compounds containing five or more fused rings that are present in the particulate phase. Benzo(a)pyrene, Indeno(1,2,3-cd)pyrene,
Table 2 Size distributions of the total particulate PAHs concentrations measured at four sites, Korea in February and May 2000 Season Winter
Spring
Period PAHs concentrations (ng m3 )
2/22 25
2/21 24
2/22 25
2/22 25
5/12 15
5/12 15
5/12 14
5/14 16
IC
YS
YP
SE
IC
YS
YP
Site SE Small particle
Back-up filter
o0.43
7th Stage
0.43 B0.65 0.65 B2.1 2.1 B3.3 3.3 B5.8 5.8 B9.0 o9.0
6th Stage 4th Stage 3rd Stage 1st Stage Total Large particles
B Stage C Stage D Stage Total
Total PAHs Small particle fraction (%) Large particle fraction (%)
8.1 B17.4 17.4 B25.8 25.8 B100 8.1 B100
18.7
61.9
23.6
28.3
3.60
18.2
8.49
20.1
65.1
18.8
17.6
4.11
16.3
18.7
59.4
21.8
55.4
3.37
18.4
8.37
14.7
15.4
55.5
16.3
25.0
3.65
15.9
9.42
13.3
17.1
64.5
17.8
15.6
3.48
18.3
9.91
12.7
16.4 106
94.9 401
15.0 113
42.7 185
3.19 21.4
14.0 101
15.6
16.2 68.0
7.77
15.5
20.3 84.3
1.42
6.05
4.57
7.13
0.64
1.01
2.21
2.88
0.30
1.20
0.39
1.13
0.51
1.45
2.09
1.97
0.37
1.19
0.72
2.20
0.31
1.53
1.76
2.76
2.09
8.44
5.68
10.46
1.46
3.99
6.06
7.61
109
410
119
195
22.9
105
74.1
91.8
98.1
97.9
95.2
94.6
93.6
96.2
91.8
91.7
1.9
2.1
4.8
5.4
6.4
3.8
8.2
8.3
Small particles (Dp p9 mm), large particles (Dp > 9 mm), unit of stage cut size: mm:
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5495
concentration than large particles. It has been known that when PAHs compounds emitted in the gaseous phases were condensed into particle phase, PAHs compounds were mostly distributed to small particles. Then, the PAHs compounds with high vapor pressures or low molecular weights evaporate and recondense onto the large particles (Allen et al., 1996). Therefore, the results also suggest that Inchon and Yangpyoung have emission sources near the sites. The ratios of PAHs in large particle to total PAHs concentrations in Yangsuri and Yangpyoung as shown in Table 3 are, however, higher than in Inchon and Seoul. If sources are near, majority of PAHs should be in the small particles as explained before. This suggests that in Yangsuri and Yangpyoung, some fraction of PAHs, especially, PAHs in large particles might be transported from urban areas. The results of this study are compared with other studied in USA in Table 4. In USA, the PAHs concentrations in urban areas (Boston, Chicago, and Houston) are higher than those in rural areas (Lake Guardian and South Haven) by a fraction of 10 or larger, as shown in Table 4. Higher ambient PAHs concentrations in urban areas are likely due to higher emissions from local sources. The PAHs concentrations of Inchon and Seoul in winter, 410 and 109 ng m3 ; respectively, were comparable to or lower than those of Boston, Chicago, and Houston, USA. However, the PAHs concentrations of Yangsuri and Yangpyoung are 3–5 times higher than Lake Guardian and South Haven, typical rural areas in USA. This shows serious PAHs pollution levels in rural areas of Korea. Therefore, Yangsuri and Yangpyoung may have local emission sources in addition to the effects of transport from outside. It is interesting to note that the PAHs level in Seoul is rather low. The sampling site at Seoul is located in a university campus with low fossil fuel combustion. This might explain the low PAHs levels.
Dibenzo(a,h)anthracene, and Benzo(g,h,i)pyrene, which contained five fused rings, are predominantly present in the particulate phase. The concentrations of these high molecular weight compounds in winter are far higher than in spring at all sites. For example, in Seoul the total concentration of these was 2:12 ng m3 in winter while in spring 0:28 ng m3 : The concentrations in winter are about 10 times higher than those in spring. It shows that the higher concentrations of PAHs in winter than spring are mainly due to higher emission while the temperature effect cannot be neglected. In both seasons, the total PAHs concentrations at Inchon were the highest followed by Yangpyoung, Yangsuri, and Seoul. This trend is contrary to the original expectation that the total PAHs concentrations at Inchon and Seoul be higher than those at Yangsuri and Yangpyoung because Inchon and Seoul have major emission sources and Yangsuri and Yangpyoung are rural areas. For all the samples, more than 60 wt% of PAHs were in particles with diameter less than 3 mm and more than 90 wt% of PAHs were in the particles with diameter less than 9 mm as shown in Table 2. It can be explained by the fact that semivolatile organic compounds (SOCs) such as PAHs are mainly distributed at fine particles (Pankow et al., 1997). Table 3 shows the ratios of the PAHs concentration to the mass concentration for small (Dp p9 mm) and large (Dp p9 mm) particles. The mass size distribution was not quantified in Yangsuri during May, only PAHs size distribution was quantified. For both size ranges, the PAHs to mass concentration ratios in winter were higher than those in spring, especially at Inchon and Yangpyoung. In addition, the ratios at Inchon and Yangpyoung were 2–5 times higher than the other two sites in winter. This suggests that Inchon and Yangpyoung have emission sources near to the sites. For all the samples, small particles contain more PAHs per unit mass
Table 3 Ratio of PAHs to the particle mass concentrations of small and large particles measured at four sites, Korea in winter and spring, 2000 (mg PAHs g1 particle1 ) Winter
Spring
SE
IC
YS
YP
Small particle Large particle Total
64.5 1.26 65.8
119 2.56 122
36.2 1.82 38.0
100 5.69 106
Ratio of PAHs in small particles to PAHs in large particles
46.4
51.0
20.0
17.7
Small particles (Dp p9 mm), large particles (Dp > 9 mmÞ:
SE 1.07 0.073 1.14 25.3
IC 20.8 0.819 21.6 14.6
YS 4.43 0.395 4.83 11.2
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3.2. Dry deposition fluxes
fluxes in winter were higher than in spring at all sites. The dry deposition fluxes of Inchon were the highest among the four sites during both seasons, and the other three sites have statistically comparable fluxes. As mentioned earlier, the sites were chosen under the assumption that Seoul and Inchon were main emission areas of PAHs. But the flux results indicate that in addition to the ambient PAHs levels, Yangsuri and Yangpyoung might have extra emission sources. The results of this study are compared with those of another study in USA, as shown in Table 5. The dry deposition fluxes of PAHs in Inchon and Seoul are lower than that in Chicago, USA except Inchon winter. However, the dry deposition fluxes of PAHs in Yangsuri and Yangpyoung are 30 times higher than South Haven and Sleeping Bear Dunes, rural areas in USA. It also shows serious PAHs pollution levels in rural areas of Korea. Usually, dry deposition flux is described as the product of the dry deposition velocity and the ambient concentration. The factors affecting dry deposition velocity are wind speed, atmospheric stability, particle density, and particle size (Sehmel, 1973). The wind speeds and ambient PAHs concentration of Inchon (4:7 m s1 ) were higher than other sites (3:5 m s1 in Seoul, 1:5 m s1 in Yangsuri, and 1:8 m s1 in Yangpyoung) based on the meteorological data (Korea Meteorological Administration, private communication). Thus, dry deposition flux of Inchon is the highest among the four sampling sites. The atmospheric PAHs concentrations of Yangsuri and Yangpyoung are higher
The total particulate PAHs dry deposition fluxes were between 10 and 24 mg m2 day1 in winter, and between 4.1 and 8:2 mg m2 day1 in spring as shown in Fig. 2. During spring, the flux measurement at Yangpyoung was not carried out due to a sampler problem. Same as the ambient PAHs concentrations, the dry deposition
Table 4 Comparison of ambient levels of PAHs with other measurement results Location
Total PAHs ðng m3 Þ
Reference
Seoul, Korea Inchon, Korea Yangsuri, Korea Yangpyoung, Korea
109/22.9 410/101 119/74.1 195
This This This This
Boston, USA Chicago, USA
194 442
Chicago, USA
428
Houston, USA Lake Gaurdian, USA South Haven, USA
119 22
Lewis et al. (1991), summer Cotham and Bidleman (1995), winter Odabasi et al. (1999), summer-fall Lewis et al. (1991), summer Simcik et al. (1997)
21
Simcik et al. (1997)
study, study, study, study,
winter/spring winter/spring winter/spring winter
Flux of particulate PAHs (µg m-2 day-1)
50 winter spring 40
30
20
10
0 Inchon
Seoul
Yangsuri
Yangpyoung
Sampling site Fig. 2. Histogram of the particulate PAHs fluxes measured with dry deposition plate: (a) Inchon and (b) Yangsuri.
S.Y. Bae et al. / Atmospheric Environment 36 (2002) 5491–5500
5497
Table 5 Comparison of the dry deposition PAHs fluxes measurement Location
Season
Mass flux ðmg m2 day1 Þ
PAHs flux (mg m2 day1 Þ
Reference
Seoul, Korea
Winter Spring Winter Spring Winter Spring Winter
340 360 97 120 180 220 32
12 5.5 24 8.2 10 4.1 11
This study
This study This study
18.0 0.7 0.2 0.3
Franz Franz Franz Franz
Inchon, Korea Yangsuri, Korea Yangpyoung, Korea Chicago, USA Over-Lake, USA South Haven, MI, USA Sleeping Bear Dunes, MI, USA
— — — —
65 12 10 3.6
that those of Seoul. But the PAHs fluxes in Seoul, Yangsuri, and Yangpyoung are similar. The wind speeds, an important factor affecting dry deposition velocity, in Seoul were the highest among three sites. Therefore, although the ambient PAHs concentrations were higher at Yangsuri and Yangpyoung than at Seoul, the dry deposition fluxes of PAHs were statistically similar at three sites. This shows that wind speeds are an important factor on dry deposition velocity and, thus, dry deposition flux. 3.3. Characteristics of individual PAH compounds In Sections 3.1 and 3.2, it was shown that Yangsuri and Yangpyoung have local sources of PAHs in addition to the transport from outside. To further understand the difference of the PAHs levels between urban and rural areas, the ambient concentrations of individual PAH compounds at each site are studied and those in Inchon and Yangsuri are shown in Fig. 3. In Inchon, phenanthrene (PHE) was the most abundant compound. Also, the concentrations of other low molecular weight PAHs in Inchon were also higher than Yangsuri and Yangpyoung. The concentrations of high molecular weight PAHs in Inchon were similar to these at other sites. This suggests that in Inchon, there are direct emission sources of PAHs. Though not shown, the PAHs compounds’ profile in Seoul is similar to that in Inchon and, thus, it is likely that they might have common emission sources. Yangsuri and Yangpyoung have different PAHs profiles from Inchon and Seoul as shown in Fig. 3. The concentrations of high molecular weight PAHs compounds in Inchon and Seoul were higher than in Yangsuri and Yangpyoung. For example, the ambient concentrations of Benzo(a)pyrene (BaP) in Inchon and Seoul were 0:73 and 0:61 ng m3 ; respec-
This study
et et et et
al. al. al. al.
(1998) (1998) (1998) (1998)
tively, while the concentrations were 0:17 and 0:53 ng m3 at Yangsuri and Yangpyoung, respectively, in winter. In spring the concentrations of BaP in Yangsuri and Yangpyoung were below the detection limits while those at Inchon and Seoul were 0.18 and 0:079 ng m3 ; respectively. Fig. 4 shows individual PAH compounds levels in the deposited particles in Inchon and Yangsuri. Inchon and Seoul have similar PAHs profiles in the deposited particles and thus, as mentioned earlier, two areas might have common emission sources as shown in Fig. 4. For instance, the flux levels increase with the increase of molecular weight until PHE in Inchon and Seoul except acenaphthalene (ACE). The value of ACE is larger than acenaphthene (ACT) in Inchon and Seoul. Since the different PAHs profiles indicate different emission sources (Daisey et al., 1995; Lee et al., 1976), it suggests a possibility that there are local emission sources of PAHs in Yangsuri and Yangpyoung. One possible source of PAHs in the rural areas is open burning of agricultural and other wastes. It has been reported that the PAHs profile depends on the type of emission sources. For example, PHE, FL, and PY are typical diesel vehicles markers and indeno(1,2,3-cd)pyrene (IcdP) and benzo(g,h,i)pyrene (BghiP) are typical gasoline vehicle markers (Harrison et al., 1996). Also, Benzo(a)pyrene (BaP) is a typical marker for coke oven in a steel work (Smith, 1984). As shown earlier, the ambient concentrations of BaP in Inchon and Seoul in winter were higher than that in Yangsuri and Yangpyoung. This suggests that BaP emitted in a steel work in Inchon might affect both Inchon and Seoul sites. In Inchon, the ambient concentration of PHE was 3–4 times higher than other sites. In Seoul, the ambient concentrations of all PAHs compound are low in winter. But the ambient
S.Y. Bae et al. / Atmospheric Environment 36 (2002) 5491–5500
5498
PAHs concentration (ng m-3)
200 small particle (winter) large particle (winter) small particle (spring) large particle (spring)
150
100
50
0 ACE ACT FLN PHE ANT FL PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
(a) Inchon
PAHs concentration (ng m-3)
100 small particle (winter) large particle (winter) small particle (spring) large particle (spring)
75
50
25
0 ACE ACT FLN PHE ANT FL (b) Yangsuri
PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
Fig. 3. Ambient PAHs concentration measured by cascade impactor for small particles and by CPRI for large particles at: (a) Inchon and (b) Yangsuri.
concentrations of IcdP and BghiP, gasoline vehicle markers, were higher than those in Inchon. This shows that in Seoul and Inchon, vehicles were the main emission sources of PAHs; but in Seoul, effects from gasoline vehicles were more prominent. In Yangsuri and Yangpyoung major emission sources were not identified. But since the ambient concentrations of PAHs at both sites were higher than Seoul and the BaP concentrations were lower than Inchon and Seoul it is likely that there are rather strong local emission sources of PAHs in Yangsuri and Yangpyoung.
4. Summary PAHs are a class of persistent organic pollutants (POPs). In Korea, spatial distribution of PAHs has not been reported yet. To control the ambient PAHs levels, it is essential to study temporal and spatial variations of PAHs and their dry deposition fluxes. The atmospheric particle mass size distributions between 0.1 and 100 mm in diameter and their deposition fluxes of PAHs were measured at four sites in the midpart of Korea in February and May 2000 to characterize the spatial and temporal variations distribution of
S.Y. Bae et al. / Atmospheric Environment 36 (2002) 5491–5500
5499
Flux of particulate PAHs (µg m-2 day-1)
15 winter spring
10
5
0 (a) Inchon
ACE ACT FLN PHE ANT FL PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
Flux of particulate PAHs (µg m-2 day-1)
15 winter spring
5
0 (b) Yangsuri
ACE ACT FLN PHE ANT FL PY BaA CHR BbF BkF BaP IcdP DahA BghiP PAHs compound
Fig. 4. The particulate PAHs compounds fluxes measured with dry deposition plate in: (a) Inchon and (b) Yangsuri.
particulate dry deposition of PAHs. Samples were collected at two urban areas: Inchon, Seoul; and two rural areas; Yangsuri and Yangpyoung between 21 and 25 February, and between 12 and 16 May 2000. The total particulate PAHs concentrations are between 22.9 and 410 ng m3 with an average of 139 ng m3 : The total particulate PAHs dry deposition fluxes are between 10 and 24 mg m2 day1 in winter, and between 4.1 and 8:2 mg m2 day1 in spring. At all sites, the ambient concentrations of PAHs and dry deposition fluxes in winter were higher than spring mainly due to higher emissions of PAHs from fuel combustion. The ambient concentrations of PAHs in
Inchon were the highest followed by Yangpyoung, Yangsuri, and Seoul. The dry deposition fluxes of Inchon were also the highest and those at other sites were statistically comparable. The fractions of PAHs in small particles (Dp p9 mm) in Inchon and Yangpyoung were higher than other sites. Further, the ambient concentrations and dry deposition fluxes of PAHs in Inchon and Seoul were comparable to lower than those in urban areas, USA, but those in Yangpyoung and Yangsuri were higher than those in rural areas, USA. Based on these observations, it was suggested that the PAHs levels in Yangpyoung and Yangsuri are affected by both local emission source and the transport from
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outside. However, in Yangpyoung and Yangsuri, no specific emission source was identified. It is recommended that to further identify and characterize high PAHs levels in rural areas of Korea, further source identification studies are needed in Korea.
Acknowledgements This paper was written with support from the Climate Environment System Research Center, an SRC program funded by the Korea Science and Engineering Foundation, the Brain Korea 21 Program, and the Ministry of Environment, Korea.
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