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Development of an improved dry and wet deposition collector and the atmospheric deposition of PAHs onto Ulsan Bay, Korea
ARTICLE IN PRESS AE International – Asia Atmospheric Environment 38 (2004) 863–871
Development of an improved dry and wet deposition collector and the atmospheric deposition of PAHs onto Ulsan Bay, Korea Byeong-Kyu Lee*, Chae-Bog Lee Department of Civil and Environmental Engineering, University of Ulsan, Moogeo-dong, Nam-gu, Ulsan 680-749, South Korea Received 24 June 2003; received in revised form 7 October 2003; accepted 21 October 2003
Abstract An improved dry and wet deposition collector was built to monitor the atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) onto water in lakes or seas. In the improved collector the evaporated solution is replenished from a water supply reservoir by a tubing pump. Water vapor produced by a mini-space heater is sent up to the wet funnel by the vacuum pump (outlet) pressure and the water vapor pressure produced at a given temperature. The condensed water vapor is supplied into the wet funnel with a constant flow rate to prevent the channel formation in the wet adsorption cartridge. In a performance test of the developed deposition collector, the average recovery rate of 16 standard PAHs was 86% when using 30 ml of CH2Cl2 as an eluent for 10 g of ENVI-18 packed in the adsorption cartridge. The drawbacks, such as evaporation of surrogate solution for dry deposition, channel formation inside wet adsorption cartridge during dry periods and expensive cost for system building, which are commonly faced with measurement of atmospheric deposition of PAHs onto water surfaces have been substantially solved in this improved collector system. The total (dry and wet) atmospheric deposition of PAHs onto Ulsan Bay during the winter was much greater than that during the summer. This was mainly due to a difference in the amounts of fossil fuel used and the prevailing wind characteristics during each season. Dry deposition of PAHs was predominant during the winter, however, wet deposition was the major deposition during the summer. Most of the PAHs deposited onto Ulsan Bay had less than or equal to 4 aromatic rings. The atmospheric deposition of the PAHs with 2, 3 and 4 aromatic rings was 38.0%, 27.8% and 24.1%, respectively. r 2003 Elsevier Ltd. All rights reserved. Keywords: PAH measurement; Channel formation; Water vapor; Seasonal variation; Fossil fuel uses
1. Introduction Most polycyclic aromatic hydrocarbons (PAHs) in the atmosphere have pyrogenic origins, such as the incomplete combustion of fossil fuels and biomass burning, that have been transported and deposited onto our ecosystem as dry and wet forms (Sheu et al., 1996; Golomb et al., 2001; Halsall et al., 2001; Garban et al., *Corresponding author. Tel.: +82-522592864; fax: 82522592629. E-mail address: [email protected] (B.-K. Lee).
2002). Since many PAHs have been found to be mutagenic and/or carcinogenic to fish and other marine organisms as well as to humans, atmospheric deposition of PAHs has been watched with great concern (Baek et al., 1991; Menzie et al., 1992; Moore, 1995). Therefore, it is worthwhile to measure the atmospheric deposition of PAHs onto water surfaces and to identify the emission sources for environmental protection (Leister and Baker, 1994; Wild and Jones, 1995; Dickhut and Gustafson, 1995; US EPA, 1997; Simcik et al., 1999). A few researchers have worked on the development of atmospheric deposition collectors that can
1352-2310/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2003.10.047
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simultaneously measure the dry and wet deposition of PAHs (Noll and Fang, 1986; Golomb et al., 1997a, b, 2001). Surrogate surface collectors have been commonly used for dry deposition measurement of PAHs because they are relatively easy to apply for field measurement. The collection methods using surrogate surface can also provide us temporal and spatial information of dry deposition with a good control of surrogate surface, exposure time and sample extraction (Lang et al., 2002). However, there are real difficulties that dry deposition obtained by use of surrogate surfaces is not directly associated with the deposition by natural surfaces or other types of surfaces. These drawbacks are particularly serious in using surrogate surfaces that are not aerodynamically designed. Water has been frequently used as surrogate surface for dry deposition measurement; however, there have been difficulties in maintaining constant water surface due to an evaporation of water in the dry collector. Adsorption cartridges for dry and wet deposition measurement of PAHs have been commonly used. For effective adsorption, wet adsorption cartridge needs to be conditioned and prevented inside channel formation particularly during dry periods. For this purpose water should be constantly supplied to adsorption cartridge during dry periods, however, it is not a simple work and requires complex instrumentation. Therefore, it is very expensive to construct the whole system to effectively measure dry and wet deposition of PAHs. Ulsan is a representative industrial city, which has the biggest petrochemical and chemical, mechanic and shipbuilding, and non-ferrous metallic industrial complex (IC), in Korea. In addition, Ulsan is a metropolitan city that has a population of about 1,100,000, wide coastal areas, many lakes and seas. The proportion of industry and vehicle emissions to the total air pollutant emissions is about 56% and 18% in Ulsan, respectively, as compared to 27% and 41% in South Korea, respectively. In Ulsan, a lot of air pollutants such as criteria air pollutants, volatile organic compounds (VOCs), and hazardous or toxic pollutants such as PAHs and heavy metals are produced by industrial activities (Ho et al., 2002). They are deposited onto Ulsan’s downtown and residential areas, mountains, rivers, lakes, and seas as well as being transported to other cities (Lee and Na, 2000; Park, 2000). Thus, the general public of Ulsan worries about the exposure potential to toxic pollutants such as PAHs and heavy metals. The purpose of this study is to build an improved deposition–collector system for simultaneous measurement of dry and wet deposition of PAHs onto water. Another purpose of this study is to figure out atmospheric deposition characteristics of PAHs onto water in Ulsan through analysis of the PAHs deposited as dry
and wet forms at Ulsan Bay during the summer and winter.
2. Development of the dry and wet deposition collectors 2.1. Analysis of the previously developed deposition collectors Water has been used as a surrogate surface to simulate pollutant deposition onto water (Davison et al., 1985; Gardner and Hewitt, 1993; Yi et al., 1997; Golomb et al., 1997a, b, 2001; Odabasi et al., 2001). However, evaporation problems of water exposed to wind or sunlight for dry periods interfered with maintaining a constant water level in the deposition buckets (Graham et al., 1988; Graham, 1990). Therefore, a water supply system to compensate for the water evaporated during dry periods was introduced into the dry collector. However, it was not easy to maintain a constant water level in dry funnel with a simple falling water supply system using gravity. Adsorption cartridge systems were used to improve the adsorption of the PAHs deposited into the dry and wet collectors. Also, there were difficulties in supplying constant amount of water required for good adsorption conditioning of the wet adsorption cartridge. In addition, channel formation inside the wet adsorption cartridge during dry periods interfered with an effective adsorption of PAHs. A micro-pump was used to solve the water evaporation problems in the dry collector and a vacuum pump was used to improve the adsorption rates in the wet collector. However, channeling phenomenon remained unsolved in the wet adsorption cartridge during dry periods. 2.2. Configuration of the improved dry and wet deposition collectors Fig. 1 shows a schematic flow diagram of the improved dry and wet deposition collector system developed in this study for simultaneous measurement of the atmospheric deposition of PAHs. The developed collector system consisted of dry and wet collectors with each having a funnel, a PAH adsorption cartridge and an individual water supply system. A shuttling lid activated by a precipitation sensor, which could be affected by changes of water content or humidity, covers the dry and wet funnels during wet and dry periods, respectively. There is a rain reservoir in the middle of the dry and wet collector systems for protection of the electronic control system during wet periods. Cone-type polypropylene (PP) funnels, instead of polyethylene (PE) buckets or funnels, were used for an easy collection of the solution containing the deposited PAHs. The top open area, the volume, and the maximum depth of the
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Atmospheric Deposition
Yes
No
Water Supply Bottle
Precipitation
Moisture Wet Funnel
Dry Funnel (Surrogate Soln)
Wet Adsorption Cartridge
Overflow
Tubing Pump
Yes
No Dry Adsorption Cartridge
Vacuum Pump
Water Vapor
Water Supply Reservoir
Overflow Chamber
Mini Heater
Wet Collector System
Piston Pump Pu mp
Dry Collector System
Fig. 1. Schematic diagram of the improved dry and wet collectors.
funnels for deposition of PAHs was 283 cm2, 19.4 cm, and 3300 cm3, respectively.
2.3. Improved dry deposition collector In the dry deposition collector, ultra-pure (deionized) water mixed with 10% by volume methanol was used as a surrogate surface (solution) for dry deposition and was filled up to the lid of the dry funnel. The surrogate solution could increase Henry’s law constants of PAH components deposited onto the water surface and thus it might slightly increase the water solubility of PAHs as compared to plain water. The surrogate solution could minimize an adsorption possibility of the PAHs, deposited onto the solution, by the inside wall surface of the dry funnel before they are adsorbed by the adsorption cartridge. The dry funnel was connected with an adsorption cartridge (tube) packed with ENVI-18 (a stationary phase, with about 17% carbon, containing octadecyl carbon as a functional surface) for PAH adsorption. A metering (piston) pump was used to pass the solution with a constant flow-rate of through the adsorption cartridge. That is, the PAHs deposited onto the surrogate surface during sampling periods were adsorbed by the adsorption cartridge with the operation of a piston pump. With adjusting the pump flow rate, the deposited PAHs might not have a longer residence time than 2 days in the dry funnel before they are sent through the adsorption cartridge. It is very important to maintain a constant deposition surface during dry deposition sampling. The evaporation problem of the surrogate solution during dry periods was solved through a constant supply of the solution from a water
(surrogate solution) supply reservoir of 20 l with a tubing pump at a flow rate of 0.8–1.2 ml/min depending upon a season change. The solution that overflowed from the dry funnel was collected in an overflow reservoir bottle. Passing the solution through the adsorption cartridge at the end of the sampling periods adsorbed the PAHs probably contained in the overflowed solution and the surrogate solution remained in the dry funnel, which were not adsorbed in the cartridge during sampling periods. If the water supply rate is properly adjusted using the seasonal evaporation rate estimated, based on to the average local meteorological data, the surrogate solution overflowed can be minimized or removed.
2.4. Improved wet deposition collector In the wet deposition collector, it was essential not to develop channels inside the PAH adsorption cartridge attached to the wet collector during dry deposition sampling periods. Therefore, the adsorption cartridge should always be kept wet or conditioned for an effective adsorption of PAHs. The inlet of the vacuum pump used to adsorb PAHs was connected with an acryl column attached to a pressure regulator and the adsorption cartridge. The outlet of the vacuum pump was connected to a water-supply bottle (WSB) and thus the pump could supply pressure onto the WSB. The WSB was heated by a mini-space heater attached to a temperature regulator and, thus, some amount of water vapor, depending upon the temperature setup at the heater, was produced. The water vapor was diverted to the neck of the wet funnel through a supply tube by the
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water vapor pressure and the vacuum pump outlet pressure. The water vapor was condensed into water at the end of a supply tube that was relatively maintaining a lower temperature than the temperature produced by the water vapor in the WSB. Constant water could then be continuously provided to the adsorption cartridge and, thus, it successfully prevented channel formation inside the wet adsorption cartridge during dry periods.
3. Atmospheric deposition measurement 3.1. Sampling The improved dry and wet deposition collector system developed in this study was placed near Ulsan Bay (35 N and 129 E) to take atmospheric deposition samples during the summer (16 June–25 August) of 1999 and the winter (12 December–6 March) between 1999 and 2000. Samples were collected on the small building roof at a height of 15 m at a typical rural site
that is located approximately 200 m from the western shore of Ulsan Bay in absence of local sources. The sampling site is also located approximately 10 km from the city center in a north-western direction, 12 km from the center of non-ferrous metallic IC in a southsouthwestern direction, 6 km from the center of petrochemical and chemical IC in a western direction, 6 km from the center of shipbuilding and mechanic IC in an eastern direction and 6 km from a power plant in a south-southwestern direction (Fig. 2). Samples of PAH deposition were taken at biweekly intervals during the summer and winter. A mixture consisting of ultra-pure water and methanol (10:1) and the PAH adsorption cartridges attached to the dry and wet deposition collectors were exchanged with new ones every 2 weeks. In this study we collected 5 dry and 5 wet atmospheric deposition samples of PAHs during the summer season and 5 dry and 4 wet deposition samples during the winter at Ulsan Bay. The meteorological data used in this study was obtained from a nearby air pollution monitoring station located about 2 km from the sampling site.
Fig. 2. Map of the sampling site.
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3.2. PAH analysis At the end of the 2-week sampling periods, the overflowed solution and the surrogate solution remaining in the dry funnel were passed through the PAH adsorption cartridge using a pump. After bringing the adsorption cartridges to an analytical laboratory, the PAHs adsorbed in the cartridges were desorbed using 30 ml of methylene chloride (CH2Cl2). The desorbed PAHs were concentrated by an evaporation of highpurity nitrogen gas of 99.99%. The recovered PAHs were analyzed by the HPLC (Varian Co.) with a UVdetector (254 nm, UV/Vis 410 Detector) and LC-PAHs column (Chrompsher 5 PAH, 4.6 mm 150 mm). The column oven (Timbleline 100) was maintained at 35 C and an eluent mixed with acetonitrile and water was used as a mobile phase (Masclet et al., 2000; Garban et al., 2002). A gradient method that began from 50:50 of acetonitrile and water was applied. The proportion of acetonitrile was gradually increased up to 0:100 by a pump (Prostar 230 Solvent Delivery Module). 16 PAH standards (Supelco, 4-8734U) were used as calibration for an analysis of PAHs. In order to check the performance of the improved dry and wet deposition collector system, the recovery rates obtained through repeated adsorption into and desorption from the adsorption cartridge of the PAH standards, spiked into the surrogate solution having similar volume to the volume of the solution used for the ambient samplings, were investigated.
4. Results and discussion 4.1. The system performance test The improved dry and wet deposition collector system for the atmospheric deposition measurement of PAHs was very stable and reliable during unattended automatic operation in the field trial. There were no big problems in normally operating the collector system during the outside sampling intervals. A surrogate solution, spiked with a standard mixture of 16 PAHs, was poured into the dry collector system and passed through the dry adsorption cartridge for PAH adsorption using a piston pump. The adsorbed PAHs were extracted with methylene chloride and analyzed by HPLC for the system performance. In 4 repeated performance tests (1st, 2nd, 3rd, 4th shown in Table 1) of the dry deposition collector developed in this study, the average recovery rate of 16 standard PAHs spiked was 85.7% when using of 30 ml of methylene chloride as an eluent for 10 g of ENVI-18 packed in the adsorption cartridge. When the amount of the eluent solution increased from 30 to 60 ml for the dry adsorption cartridge examined, the average recovery rate of 16
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Table 1 Recovery rates of 16 standard PAHs in the dry and wet collector (unit: %) PAHs
Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenzo(a; h)anthracene Benzo(ghi)perylene Average
4 repeated tests
Average S.D.
1st
2nd
3rd
4th
116.5 80.2 79.3 81.6 79.4 74.9 71.1 77.2 87.6 90.1 98.4 91.5 73.3 92.4 86.5 100.7 86.3
100.7 84.6 72.6 89.9 83.4 84.3 80.5 68.3 79.0 77.7 88.6 76.9 60.9 97.0 84.2 95.3 82.7
98.6 102.0 74.4 75.3 71.6 75.2 68.2 65.7 86.0 94.3 84.2 85.6 78.1 98.6 84.7 98.1 83.9
110.1 95.3 87.7 72.2 96.4 64.1 65.4 83.0 92.6 81.5 86.5 100.2 80.8 112.7 95.1 113.6 89.8
106.4 90.7 78.5 79.8 82.9 74.6 71.2 73.5 86.3 85.9 89.7 88.6 73.3 100.2 87.8 102.5 85.7
8.3 10.0 6.7 7.6 10.4 8.2 6.5 8.2 5.7 7.7 6.2 9.8 8.8 8.7 5.1 8.0 7.9
PAHs increased from 86% to 90%. That is, to completely elute the PAHs adsorbed in the adsorption cartridge, enough elution solvent had to be used and a more effective elution method had to be designed. After the dry and wet deposition collector was operated on a building roof at the University of Ulsan for a dry period of 2 weeks with early summer season characteristics as a system performance check, the wet adsorption cartridge was cut with a micro-saw and it was carefully examined with the naked eye. The checked adsorption cartridge was still wet and no damage such as channels or unusual deformations was found. The adsorption, desorption, and recovery rates of PAHs for the improved dry and wet deposition collector developed in this study proved to be equivalent to or better than previously developed collectors when they were compared (Golomb et al., 1997a). The cost to build the improved dry and wet deposition collector system was much lower (about 60–65% less) than those of the dry and wet collector systems developed by other researchers. This is due to the fact that we greatly reduced the number of pumps used for adsorbing PAHs, compensating for evaporated surrogate solution in the dry collector and preventing channel formation in the wet adsorption cartridge. This was also due to the use of PP funnels, which have a low material cost and an easy tapering process, instead of Teflon coated PE buckets or stainless-steel funnels as a receiving tool for PAHs deposited from the atmosphere. Even though the PP funnel may result in small artifacts of PAH adsorption to PP, the artifacts in this study
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seemed not to be identified. From the good average recovery rates of up to 90%, depending upon the extraction volume of methylene chloride, shown in our repeated system performance tests, we infer a very low possibility of artifact formation. Even if an artifact formation were produced, a Teflon coating inside the PP funnel would greatly mitigate the problem. Also, costeffective construction would adequately compensate for the slight possibility of artifact formation. 4.2. Seasonal variations in the atmospheric deposition rate of PAHs Table 2 shows the dry and wet atmospheric deposition rates of the selected 16 PAHs at Ulsan Bay during the summer of 1999 and the winter between 1999 and 2000. The average atmospheric deposition rates of PAHs at Ulsan Bay during the winter were much higher than those during the summer. The lower deposition rate during the summer could be associated with the hot summer temperature, rising up to 35–36 C, which could reduce the atmospheric deposition of gas or vapor phase PAHs. Since the length of daytime during the summer in Ulsan is about 1.7–1.8 times as long as that of the winter, there is a possibility that significant amount of PAHs by photochemical reactions could disappear or be thermally decomposed (Kiss et al., 2001). The serious increase in the atmospheric deposition rate of PAHs during the winter onto Ulsan Bay may be also due to a significantly increased fossil fuel use during the winter as compared to the summer. There is the significant difference (21 C) in the average temperature
between the winter of 3 C and the summer of 24 C in Ulsan. Thus use of kerosene, heavy gas oil, briquette, coal and wood for residential and commercial space heating during the winter season became 10 times as much as that during the summer. The significant increase in wood burning and fossil fuel combustion during the winter could contribute to the high deposition rate of PAHs. Another reason for higher dry deposition rate during the winter could be due to the lower mixing height and different wind characteristics prevailing in the winter as compared to the summer (Golomb et al., 1997a, b). Fig. 3 shows the average wind roses observed in Ulsan during the period of this study, respectively. The prevailing winds during the summer in Ulsan did not include significant emission sources of PAHs. The emissions from shipbuilding and mechanical IC may not be significant sources of PAHs at Ulsan Bay during the summer because there are mountains of about 250 m height between the emission sources and the receptor. Also, the power plants and non-ferrous metallic IC, having high PAH emission strength, might not be the significant sources of the PAHs deposited onto Ulsan Bay. It is because the relative proportion of the winds blowing from the sources is very minor. The prevailing winds of the winter were coming from the directions of Ulsan downtown areas which might carry significant amounts of PAHs produced from an increased fossil fuel use during the winter season. However, the emissions from the industrial complex zones may not significantly contribute to the PAH deposition onto Ulsan Bay during the winter because of the quite low proportion of the winds from the sources.
Table 2 Average dry and wet deposition rates of PAHs at Ulsan Bay during the winter and summer
Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenzo(a; h)anthracene Benzo(g; h; i)perylene a
Dry deposition rate (ng/m2 h)
Wet deposition rate (ng/m2 cm)
Winter (n ¼ 5a)
Summer (n ¼ 5a)
Winter (n ¼ 4a)
Summer (n ¼ 5a)
5.9372.11 0.8270.42 2.8671.10 1.4670.40 1.4770.52 0.2170.17 3.5271.49 1.0570.37 0.1570.02 0.0270.01 0.0370.01 0.1570.03 0.0270.01 0.0370.02 1.1270.01 0.0170.01
1.1070.53 0.0570.03 0.0470.02 0.0170.01 0.1670.05 0.0170.01 0.0370.02 1.5570.54 0.0770.05 0.1270.08 0.0370.02 0.0770.04 0.2270.05 0.1170.09 0.0670.02 0.0070.00
2082.707436.84 162.92771.13 81.52734.05 28.0378.26 36.8575.81 164.04768.45 248.68753.38 138.36736.40 49.80719.54 5.0373.35 25.01714.96 5.0373.02 10.0576.25 45.00726.24 183.80728.14 16.53713.07
4.1671.77 1.1770.85 39.17711.22 0.0870.04 0.8970.20 0.1270.08 7.3472.78 23.2077.14 0.0470.04 0.5670.36 0.3270.20 0.1670.08 2.8671.93 0.8570.56 3.1171.94 1.4971.01
Each measurement takes 2 weeks and thus 5 measurements mean 10-week sampling.
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Fig. 3. Average wind rose observed during the summer and the winter in Ulsan.
The wet deposition rate during the winter was extremely greater than the wet deposition rate during the summer (Table 2). This high deposition rate in the winter might be associated with the increased PAH emission during the winter as already described above. In addition, the high wet deposition rate might be significantly related with the increased Henry’s law constants of PAHs due to the low temperature during the winter. Thus, the water solubility increase of the gaseous or vapor phase PAHs, such as naphthalene which has high Henry’s law constant, might be a cause of the increase of wet deposition rate in the winter. The increased surface area per unit mass of snow as compared to rain might be also responsible for the high deposition rate in the winter. In this study, however, the contribution of snow to the high deposition rate might not be significant because of the minor precipitation as snow forms under the study period. 4.3. Comparison of dry and wet deposition of PAHs In analysis of total deposition of PAHs onto Ulsan Bay during the winter, the amount of the PAHs deposited as dry forms was 1.6 times as high as the wet deposition. However, the total amount of PAHs deposited as wet forms during the summer were about 1.4 times as high as the total dry deposition during the summer. The winter weather had a low temperature, a low humidity of 47% and a relatively small amount of precipitation of 60 ml. However, the summer weather had a high temperature, a high humidity of 75% and a significantly high precipitation of 790 ml. Even though the precipitation during the winter was much less than
the summer, the total wet deposition during the winter was much greater than the total wet deposition during the summer. From this fact, it is inferred that the total amount of wet deposition is highly dependent upon the emission strength of the sources and temperature, and might be also dependent on characteristics of the winds blowing from the sources rather than the amount of precipitation. An analysis of the total deposition of 16 PAHs deposited onto Ulsan Bay during the winter and the summer showed that 89.9% of the PAHs deposited had less than or equal to 4 aromatic rings; 2, 3 and 4 aromatic rings was 38.0%, 27.8% and 24.1%, respectively. Atmospheric deposition of the PAHs, having high molecular weight and low Henry’s law constant, on Ulsan Bay was much less than that of the PAHs with low molecular weight and high Henry’s law constant characteristics (Offenberg and Baker, 2002; Bamford et al., 1999; Park et al., 2001). Major components of the PAHs deposited onto Ulsan Bay consisted of naphthalene (2 rings) of 38.0%, acenaphthene (3 rings) of 13.1%, fluoranthene (4 rings) of 12.4% and pyrene (4 rings) of 10.3%, respectively. In particular, naphthalene was the most prominent bicyclic hydrocarbon form deposited onto Ulsan Bay during the winter and its wet deposition was more important than its dry deposition. The high water solubility of naphthalene due to high Henry’s law constant could increase its wet deposition during the winter (Mackay et al., 1992; Golomb et al., 1997a, b). However, high vapor pressure and short lifetime of naphthalene could contribute to its revolatilization and deterioration during the high temperature season, and thus they could be a cause of its lower
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deposition during the summer (Golomb et al., 1997a, b; Price et al., 2001).
5. Summary and conclusion An improved dry and wet collector system for the measurement of the atmospheric deposition of PAHs onto water surfaces has been successfully constructed. The building costs of the collector system are much lower than those of previous dry and wet collector systems. Evaporation of the surrogate solution in the dry collector was overcome by a constant supply of the surrogate solution. The formation of channels inside the wet adsorption cartridge was prevented by continuously providing water formed by a condensation of water vapor. The total amounts of PAHs deposited onto Ulsan Bay during the winter were much greater than during the summer. The increased emission sources of PAHs and lower temperature as well as the direction and distribution of the prevailing winds blowing from the sources could seriously increase the atmospheric deposition of PAHs onto Ulsan Bay during the winter. The PAHs deposited onto Ulsan Bay during the winter and the summer were mainly identified as dry deposition and wet deposition, respectively. 89.9% of the PAHs deposited onto Ulsan Bay had less than or equal to 4 aromatic rings; 2, 3 and 4 aromatic rings was 38.0%, 27.8% and 24.1%, respectively. Atmospheric deposition of the PAHs with high molecular weight and low Henry’s law constant was much less than those of the PAHs with low molecular weight and high Henry’s law constant.
Acknowledgements This study was supported by the Research Funds of the University of Ulsan. The authors wish to acknowledge the excellent assistance provided by Dr. Dan S. Golomb and George Fisher at the University of Massachusetts, Lowell, MA.
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ARTICLE IN PRESS B.-K. Lee, C.-B. Lee / Atmospheric Environment 38 (2004) 863–871 Masclet, P., Hoyau, V., Jaffrezo, J.L., Cachier, H., 2000. Polycyclic aromatic hydrocarbon deposition on the ice sheet of Greenland. Part I: superficial snow. Atmospheric Environment 34, 3195–3207. Moore, M., 1995. Mutagenesis and carcinogenesis of PAHs in the marine environment. In: Source, Fate and Effects of PAHs in Massachusetts Bay. Massachusetts Bay Program. US Environmental Protection Agency, Boston, MA. Menzie, C.A., Potocki, B., Santodonato, J., 1992. Exposure to carcinogenic PAHs in the environment. Environmental Science and Technology 26, 1278–1284. Noll, K.E., Fang, K.Y.P., 1986. A rotary impactor for size selective sampling of atmospheric coarse particles. Proceedings of the Air Pollution Control Association 79th Annual Meeting, Paper No. 86-40.2, Minneapolis, MN. Odabasi, M., Sofuoglu, A., Holsen, T.M., 2001. Mass transfer coefficients for polycyclic aromatic hydrocarbons (PAHs) to the water surface sampler: comparison to modeled results. Atmospheric Environment 35, 1655–1662. Offenberg, J.H., Baker, J.E., 2002. The influence of aerosol size and organic content on gas/particle partitioning of polycyclic aromatic hydrocarbons. Atmospheric Environment 36, 1205–1220. Park, J.-S., Wade, T.L., Sweet, S., 2001. Atmospheric deposition of polycyclic aromatic hydrocarbons and deposition to
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Galveston Bay, Texas, USA. Atmospheric Environment 35, 3214–3249. Park, J.Y., 2000. Uses of energy in Ulsan. Annual Report of the Metropolitan Ulsan, pp. 197–198. Price, C., Brannon, J., Yost, S., Sanchez, F., Thibodeaux, L., Valsaraj, K., Ravikrishna, R., 2001. Volatile losses from resuspended dredged material, ERDC/TN EEDP-02-30, pp. 1–7 (March 2001). Simcik, M., Eisenreich, S.J., Lioy, P.J., 1999. Source apportionment and source/sink relationships of PAHs in the coastal atmosphere of Chicago and lake Michigan. Atmospheric Environment 33, 5071–5079. Sheu, H.-Li., Lee, W.-J., Lin, S.J., Fang, G.C., Chang, H.-C., You, W.-C., 1996. Particle-bound PAH content in ambient air. Environmental Pollution 96, 369–382. US EPA, 1997. Deposition of air pollutants to the Great Waters. First Report to Congress, EPA-453/R-93-055, Office of Air Quality Planning and Standards, Research Triangle Park, NC. Wild, S.R., Jones, K.C., 1995. Polynuclear aromatic hydrocarbons in the United Kingdom environment: a preliminary source inventory and budget. Environmental Pollution 88, 91–108. 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.
Development of an improved dry and wet deposition collector and the atmospheric deposition of PAHs onto Ulsan Bay, Korea Byeong-Kyu Lee*, Chae-Bog Lee Department of Civil and Environmental Engineering, University of Ulsan, Moogeo-dong, Nam-gu, Ulsan 680-749, South Korea Received 24 June 2003; received in revised form 7 October 2003; accepted 21 October 2003
Abstract An improved dry and wet deposition collector was built to monitor the atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) onto water in lakes or seas. In the improved collector the evaporated solution is replenished from a water supply reservoir by a tubing pump. Water vapor produced by a mini-space heater is sent up to the wet funnel by the vacuum pump (outlet) pressure and the water vapor pressure produced at a given temperature. The condensed water vapor is supplied into the wet funnel with a constant flow rate to prevent the channel formation in the wet adsorption cartridge. In a performance test of the developed deposition collector, the average recovery rate of 16 standard PAHs was 86% when using 30 ml of CH2Cl2 as an eluent for 10 g of ENVI-18 packed in the adsorption cartridge. The drawbacks, such as evaporation of surrogate solution for dry deposition, channel formation inside wet adsorption cartridge during dry periods and expensive cost for system building, which are commonly faced with measurement of atmospheric deposition of PAHs onto water surfaces have been substantially solved in this improved collector system. The total (dry and wet) atmospheric deposition of PAHs onto Ulsan Bay during the winter was much greater than that during the summer. This was mainly due to a difference in the amounts of fossil fuel used and the prevailing wind characteristics during each season. Dry deposition of PAHs was predominant during the winter, however, wet deposition was the major deposition during the summer. Most of the PAHs deposited onto Ulsan Bay had less than or equal to 4 aromatic rings. The atmospheric deposition of the PAHs with 2, 3 and 4 aromatic rings was 38.0%, 27.8% and 24.1%, respectively. r 2003 Elsevier Ltd. All rights reserved. Keywords: PAH measurement; Channel formation; Water vapor; Seasonal variation; Fossil fuel uses
1. Introduction Most polycyclic aromatic hydrocarbons (PAHs) in the atmosphere have pyrogenic origins, such as the incomplete combustion of fossil fuels and biomass burning, that have been transported and deposited onto our ecosystem as dry and wet forms (Sheu et al., 1996; Golomb et al., 2001; Halsall et al., 2001; Garban et al., *Corresponding author. Tel.: +82-522592864; fax: 82522592629. E-mail address: [email protected] (B.-K. Lee).
2002). Since many PAHs have been found to be mutagenic and/or carcinogenic to fish and other marine organisms as well as to humans, atmospheric deposition of PAHs has been watched with great concern (Baek et al., 1991; Menzie et al., 1992; Moore, 1995). Therefore, it is worthwhile to measure the atmospheric deposition of PAHs onto water surfaces and to identify the emission sources for environmental protection (Leister and Baker, 1994; Wild and Jones, 1995; Dickhut and Gustafson, 1995; US EPA, 1997; Simcik et al., 1999). A few researchers have worked on the development of atmospheric deposition collectors that can
1352-2310/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2003.10.047
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simultaneously measure the dry and wet deposition of PAHs (Noll and Fang, 1986; Golomb et al., 1997a, b, 2001). Surrogate surface collectors have been commonly used for dry deposition measurement of PAHs because they are relatively easy to apply for field measurement. The collection methods using surrogate surface can also provide us temporal and spatial information of dry deposition with a good control of surrogate surface, exposure time and sample extraction (Lang et al., 2002). However, there are real difficulties that dry deposition obtained by use of surrogate surfaces is not directly associated with the deposition by natural surfaces or other types of surfaces. These drawbacks are particularly serious in using surrogate surfaces that are not aerodynamically designed. Water has been frequently used as surrogate surface for dry deposition measurement; however, there have been difficulties in maintaining constant water surface due to an evaporation of water in the dry collector. Adsorption cartridges for dry and wet deposition measurement of PAHs have been commonly used. For effective adsorption, wet adsorption cartridge needs to be conditioned and prevented inside channel formation particularly during dry periods. For this purpose water should be constantly supplied to adsorption cartridge during dry periods, however, it is not a simple work and requires complex instrumentation. Therefore, it is very expensive to construct the whole system to effectively measure dry and wet deposition of PAHs. Ulsan is a representative industrial city, which has the biggest petrochemical and chemical, mechanic and shipbuilding, and non-ferrous metallic industrial complex (IC), in Korea. In addition, Ulsan is a metropolitan city that has a population of about 1,100,000, wide coastal areas, many lakes and seas. The proportion of industry and vehicle emissions to the total air pollutant emissions is about 56% and 18% in Ulsan, respectively, as compared to 27% and 41% in South Korea, respectively. In Ulsan, a lot of air pollutants such as criteria air pollutants, volatile organic compounds (VOCs), and hazardous or toxic pollutants such as PAHs and heavy metals are produced by industrial activities (Ho et al., 2002). They are deposited onto Ulsan’s downtown and residential areas, mountains, rivers, lakes, and seas as well as being transported to other cities (Lee and Na, 2000; Park, 2000). Thus, the general public of Ulsan worries about the exposure potential to toxic pollutants such as PAHs and heavy metals. The purpose of this study is to build an improved deposition–collector system for simultaneous measurement of dry and wet deposition of PAHs onto water. Another purpose of this study is to figure out atmospheric deposition characteristics of PAHs onto water in Ulsan through analysis of the PAHs deposited as dry
and wet forms at Ulsan Bay during the summer and winter.
2. Development of the dry and wet deposition collectors 2.1. Analysis of the previously developed deposition collectors Water has been used as a surrogate surface to simulate pollutant deposition onto water (Davison et al., 1985; Gardner and Hewitt, 1993; Yi et al., 1997; Golomb et al., 1997a, b, 2001; Odabasi et al., 2001). However, evaporation problems of water exposed to wind or sunlight for dry periods interfered with maintaining a constant water level in the deposition buckets (Graham et al., 1988; Graham, 1990). Therefore, a water supply system to compensate for the water evaporated during dry periods was introduced into the dry collector. However, it was not easy to maintain a constant water level in dry funnel with a simple falling water supply system using gravity. Adsorption cartridge systems were used to improve the adsorption of the PAHs deposited into the dry and wet collectors. Also, there were difficulties in supplying constant amount of water required for good adsorption conditioning of the wet adsorption cartridge. In addition, channel formation inside the wet adsorption cartridge during dry periods interfered with an effective adsorption of PAHs. A micro-pump was used to solve the water evaporation problems in the dry collector and a vacuum pump was used to improve the adsorption rates in the wet collector. However, channeling phenomenon remained unsolved in the wet adsorption cartridge during dry periods. 2.2. Configuration of the improved dry and wet deposition collectors Fig. 1 shows a schematic flow diagram of the improved dry and wet deposition collector system developed in this study for simultaneous measurement of the atmospheric deposition of PAHs. The developed collector system consisted of dry and wet collectors with each having a funnel, a PAH adsorption cartridge and an individual water supply system. A shuttling lid activated by a precipitation sensor, which could be affected by changes of water content or humidity, covers the dry and wet funnels during wet and dry periods, respectively. There is a rain reservoir in the middle of the dry and wet collector systems for protection of the electronic control system during wet periods. Cone-type polypropylene (PP) funnels, instead of polyethylene (PE) buckets or funnels, were used for an easy collection of the solution containing the deposited PAHs. The top open area, the volume, and the maximum depth of the
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Atmospheric Deposition
Yes
No
Water Supply Bottle
Precipitation
Moisture Wet Funnel
Dry Funnel (Surrogate Soln)
Wet Adsorption Cartridge
Overflow
Tubing Pump
Yes
No Dry Adsorption Cartridge
Vacuum Pump
Water Vapor
Water Supply Reservoir
Overflow Chamber
Mini Heater
Wet Collector System
Piston Pump Pu mp
Dry Collector System
Fig. 1. Schematic diagram of the improved dry and wet collectors.
funnels for deposition of PAHs was 283 cm2, 19.4 cm, and 3300 cm3, respectively.
2.3. Improved dry deposition collector In the dry deposition collector, ultra-pure (deionized) water mixed with 10% by volume methanol was used as a surrogate surface (solution) for dry deposition and was filled up to the lid of the dry funnel. The surrogate solution could increase Henry’s law constants of PAH components deposited onto the water surface and thus it might slightly increase the water solubility of PAHs as compared to plain water. The surrogate solution could minimize an adsorption possibility of the PAHs, deposited onto the solution, by the inside wall surface of the dry funnel before they are adsorbed by the adsorption cartridge. The dry funnel was connected with an adsorption cartridge (tube) packed with ENVI-18 (a stationary phase, with about 17% carbon, containing octadecyl carbon as a functional surface) for PAH adsorption. A metering (piston) pump was used to pass the solution with a constant flow-rate of through the adsorption cartridge. That is, the PAHs deposited onto the surrogate surface during sampling periods were adsorbed by the adsorption cartridge with the operation of a piston pump. With adjusting the pump flow rate, the deposited PAHs might not have a longer residence time than 2 days in the dry funnel before they are sent through the adsorption cartridge. It is very important to maintain a constant deposition surface during dry deposition sampling. The evaporation problem of the surrogate solution during dry periods was solved through a constant supply of the solution from a water
(surrogate solution) supply reservoir of 20 l with a tubing pump at a flow rate of 0.8–1.2 ml/min depending upon a season change. The solution that overflowed from the dry funnel was collected in an overflow reservoir bottle. Passing the solution through the adsorption cartridge at the end of the sampling periods adsorbed the PAHs probably contained in the overflowed solution and the surrogate solution remained in the dry funnel, which were not adsorbed in the cartridge during sampling periods. If the water supply rate is properly adjusted using the seasonal evaporation rate estimated, based on to the average local meteorological data, the surrogate solution overflowed can be minimized or removed.
2.4. Improved wet deposition collector In the wet deposition collector, it was essential not to develop channels inside the PAH adsorption cartridge attached to the wet collector during dry deposition sampling periods. Therefore, the adsorption cartridge should always be kept wet or conditioned for an effective adsorption of PAHs. The inlet of the vacuum pump used to adsorb PAHs was connected with an acryl column attached to a pressure regulator and the adsorption cartridge. The outlet of the vacuum pump was connected to a water-supply bottle (WSB) and thus the pump could supply pressure onto the WSB. The WSB was heated by a mini-space heater attached to a temperature regulator and, thus, some amount of water vapor, depending upon the temperature setup at the heater, was produced. The water vapor was diverted to the neck of the wet funnel through a supply tube by the
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water vapor pressure and the vacuum pump outlet pressure. The water vapor was condensed into water at the end of a supply tube that was relatively maintaining a lower temperature than the temperature produced by the water vapor in the WSB. Constant water could then be continuously provided to the adsorption cartridge and, thus, it successfully prevented channel formation inside the wet adsorption cartridge during dry periods.
3. Atmospheric deposition measurement 3.1. Sampling The improved dry and wet deposition collector system developed in this study was placed near Ulsan Bay (35 N and 129 E) to take atmospheric deposition samples during the summer (16 June–25 August) of 1999 and the winter (12 December–6 March) between 1999 and 2000. Samples were collected on the small building roof at a height of 15 m at a typical rural site
that is located approximately 200 m from the western shore of Ulsan Bay in absence of local sources. The sampling site is also located approximately 10 km from the city center in a north-western direction, 12 km from the center of non-ferrous metallic IC in a southsouthwestern direction, 6 km from the center of petrochemical and chemical IC in a western direction, 6 km from the center of shipbuilding and mechanic IC in an eastern direction and 6 km from a power plant in a south-southwestern direction (Fig. 2). Samples of PAH deposition were taken at biweekly intervals during the summer and winter. A mixture consisting of ultra-pure water and methanol (10:1) and the PAH adsorption cartridges attached to the dry and wet deposition collectors were exchanged with new ones every 2 weeks. In this study we collected 5 dry and 5 wet atmospheric deposition samples of PAHs during the summer season and 5 dry and 4 wet deposition samples during the winter at Ulsan Bay. The meteorological data used in this study was obtained from a nearby air pollution monitoring station located about 2 km from the sampling site.
Fig. 2. Map of the sampling site.
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3.2. PAH analysis At the end of the 2-week sampling periods, the overflowed solution and the surrogate solution remaining in the dry funnel were passed through the PAH adsorption cartridge using a pump. After bringing the adsorption cartridges to an analytical laboratory, the PAHs adsorbed in the cartridges were desorbed using 30 ml of methylene chloride (CH2Cl2). The desorbed PAHs were concentrated by an evaporation of highpurity nitrogen gas of 99.99%. The recovered PAHs were analyzed by the HPLC (Varian Co.) with a UVdetector (254 nm, UV/Vis 410 Detector) and LC-PAHs column (Chrompsher 5 PAH, 4.6 mm 150 mm). The column oven (Timbleline 100) was maintained at 35 C and an eluent mixed with acetonitrile and water was used as a mobile phase (Masclet et al., 2000; Garban et al., 2002). A gradient method that began from 50:50 of acetonitrile and water was applied. The proportion of acetonitrile was gradually increased up to 0:100 by a pump (Prostar 230 Solvent Delivery Module). 16 PAH standards (Supelco, 4-8734U) were used as calibration for an analysis of PAHs. In order to check the performance of the improved dry and wet deposition collector system, the recovery rates obtained through repeated adsorption into and desorption from the adsorption cartridge of the PAH standards, spiked into the surrogate solution having similar volume to the volume of the solution used for the ambient samplings, were investigated.
4. Results and discussion 4.1. The system performance test The improved dry and wet deposition collector system for the atmospheric deposition measurement of PAHs was very stable and reliable during unattended automatic operation in the field trial. There were no big problems in normally operating the collector system during the outside sampling intervals. A surrogate solution, spiked with a standard mixture of 16 PAHs, was poured into the dry collector system and passed through the dry adsorption cartridge for PAH adsorption using a piston pump. The adsorbed PAHs were extracted with methylene chloride and analyzed by HPLC for the system performance. In 4 repeated performance tests (1st, 2nd, 3rd, 4th shown in Table 1) of the dry deposition collector developed in this study, the average recovery rate of 16 standard PAHs spiked was 85.7% when using of 30 ml of methylene chloride as an eluent for 10 g of ENVI-18 packed in the adsorption cartridge. When the amount of the eluent solution increased from 30 to 60 ml for the dry adsorption cartridge examined, the average recovery rate of 16
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Table 1 Recovery rates of 16 standard PAHs in the dry and wet collector (unit: %) PAHs
Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenzo(a; h)anthracene Benzo(ghi)perylene Average
4 repeated tests
Average S.D.
1st
2nd
3rd
4th
116.5 80.2 79.3 81.6 79.4 74.9 71.1 77.2 87.6 90.1 98.4 91.5 73.3 92.4 86.5 100.7 86.3
100.7 84.6 72.6 89.9 83.4 84.3 80.5 68.3 79.0 77.7 88.6 76.9 60.9 97.0 84.2 95.3 82.7
98.6 102.0 74.4 75.3 71.6 75.2 68.2 65.7 86.0 94.3 84.2 85.6 78.1 98.6 84.7 98.1 83.9
110.1 95.3 87.7 72.2 96.4 64.1 65.4 83.0 92.6 81.5 86.5 100.2 80.8 112.7 95.1 113.6 89.8
106.4 90.7 78.5 79.8 82.9 74.6 71.2 73.5 86.3 85.9 89.7 88.6 73.3 100.2 87.8 102.5 85.7
8.3 10.0 6.7 7.6 10.4 8.2 6.5 8.2 5.7 7.7 6.2 9.8 8.8 8.7 5.1 8.0 7.9
PAHs increased from 86% to 90%. That is, to completely elute the PAHs adsorbed in the adsorption cartridge, enough elution solvent had to be used and a more effective elution method had to be designed. After the dry and wet deposition collector was operated on a building roof at the University of Ulsan for a dry period of 2 weeks with early summer season characteristics as a system performance check, the wet adsorption cartridge was cut with a micro-saw and it was carefully examined with the naked eye. The checked adsorption cartridge was still wet and no damage such as channels or unusual deformations was found. The adsorption, desorption, and recovery rates of PAHs for the improved dry and wet deposition collector developed in this study proved to be equivalent to or better than previously developed collectors when they were compared (Golomb et al., 1997a). The cost to build the improved dry and wet deposition collector system was much lower (about 60–65% less) than those of the dry and wet collector systems developed by other researchers. This is due to the fact that we greatly reduced the number of pumps used for adsorbing PAHs, compensating for evaporated surrogate solution in the dry collector and preventing channel formation in the wet adsorption cartridge. This was also due to the use of PP funnels, which have a low material cost and an easy tapering process, instead of Teflon coated PE buckets or stainless-steel funnels as a receiving tool for PAHs deposited from the atmosphere. Even though the PP funnel may result in small artifacts of PAH adsorption to PP, the artifacts in this study
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seemed not to be identified. From the good average recovery rates of up to 90%, depending upon the extraction volume of methylene chloride, shown in our repeated system performance tests, we infer a very low possibility of artifact formation. Even if an artifact formation were produced, a Teflon coating inside the PP funnel would greatly mitigate the problem. Also, costeffective construction would adequately compensate for the slight possibility of artifact formation. 4.2. Seasonal variations in the atmospheric deposition rate of PAHs Table 2 shows the dry and wet atmospheric deposition rates of the selected 16 PAHs at Ulsan Bay during the summer of 1999 and the winter between 1999 and 2000. The average atmospheric deposition rates of PAHs at Ulsan Bay during the winter were much higher than those during the summer. The lower deposition rate during the summer could be associated with the hot summer temperature, rising up to 35–36 C, which could reduce the atmospheric deposition of gas or vapor phase PAHs. Since the length of daytime during the summer in Ulsan is about 1.7–1.8 times as long as that of the winter, there is a possibility that significant amount of PAHs by photochemical reactions could disappear or be thermally decomposed (Kiss et al., 2001). The serious increase in the atmospheric deposition rate of PAHs during the winter onto Ulsan Bay may be also due to a significantly increased fossil fuel use during the winter as compared to the summer. There is the significant difference (21 C) in the average temperature
between the winter of 3 C and the summer of 24 C in Ulsan. Thus use of kerosene, heavy gas oil, briquette, coal and wood for residential and commercial space heating during the winter season became 10 times as much as that during the summer. The significant increase in wood burning and fossil fuel combustion during the winter could contribute to the high deposition rate of PAHs. Another reason for higher dry deposition rate during the winter could be due to the lower mixing height and different wind characteristics prevailing in the winter as compared to the summer (Golomb et al., 1997a, b). Fig. 3 shows the average wind roses observed in Ulsan during the period of this study, respectively. The prevailing winds during the summer in Ulsan did not include significant emission sources of PAHs. The emissions from shipbuilding and mechanical IC may not be significant sources of PAHs at Ulsan Bay during the summer because there are mountains of about 250 m height between the emission sources and the receptor. Also, the power plants and non-ferrous metallic IC, having high PAH emission strength, might not be the significant sources of the PAHs deposited onto Ulsan Bay. It is because the relative proportion of the winds blowing from the sources is very minor. The prevailing winds of the winter were coming from the directions of Ulsan downtown areas which might carry significant amounts of PAHs produced from an increased fossil fuel use during the winter season. However, the emissions from the industrial complex zones may not significantly contribute to the PAH deposition onto Ulsan Bay during the winter because of the quite low proportion of the winds from the sources.
Table 2 Average dry and wet deposition rates of PAHs at Ulsan Bay during the winter and summer
Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Indeno(1,2,3-cd)pyrene Dibenzo(a; h)anthracene Benzo(g; h; i)perylene a
Dry deposition rate (ng/m2 h)
Wet deposition rate (ng/m2 cm)
Winter (n ¼ 5a)
Summer (n ¼ 5a)
Winter (n ¼ 4a)
Summer (n ¼ 5a)
5.9372.11 0.8270.42 2.8671.10 1.4670.40 1.4770.52 0.2170.17 3.5271.49 1.0570.37 0.1570.02 0.0270.01 0.0370.01 0.1570.03 0.0270.01 0.0370.02 1.1270.01 0.0170.01
1.1070.53 0.0570.03 0.0470.02 0.0170.01 0.1670.05 0.0170.01 0.0370.02 1.5570.54 0.0770.05 0.1270.08 0.0370.02 0.0770.04 0.2270.05 0.1170.09 0.0670.02 0.0070.00
2082.707436.84 162.92771.13 81.52734.05 28.0378.26 36.8575.81 164.04768.45 248.68753.38 138.36736.40 49.80719.54 5.0373.35 25.01714.96 5.0373.02 10.0576.25 45.00726.24 183.80728.14 16.53713.07
4.1671.77 1.1770.85 39.17711.22 0.0870.04 0.8970.20 0.1270.08 7.3472.78 23.2077.14 0.0470.04 0.5670.36 0.3270.20 0.1670.08 2.8671.93 0.8570.56 3.1171.94 1.4971.01
Each measurement takes 2 weeks and thus 5 measurements mean 10-week sampling.
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Fig. 3. Average wind rose observed during the summer and the winter in Ulsan.
The wet deposition rate during the winter was extremely greater than the wet deposition rate during the summer (Table 2). This high deposition rate in the winter might be associated with the increased PAH emission during the winter as already described above. In addition, the high wet deposition rate might be significantly related with the increased Henry’s law constants of PAHs due to the low temperature during the winter. Thus, the water solubility increase of the gaseous or vapor phase PAHs, such as naphthalene which has high Henry’s law constant, might be a cause of the increase of wet deposition rate in the winter. The increased surface area per unit mass of snow as compared to rain might be also responsible for the high deposition rate in the winter. In this study, however, the contribution of snow to the high deposition rate might not be significant because of the minor precipitation as snow forms under the study period. 4.3. Comparison of dry and wet deposition of PAHs In analysis of total deposition of PAHs onto Ulsan Bay during the winter, the amount of the PAHs deposited as dry forms was 1.6 times as high as the wet deposition. However, the total amount of PAHs deposited as wet forms during the summer were about 1.4 times as high as the total dry deposition during the summer. The winter weather had a low temperature, a low humidity of 47% and a relatively small amount of precipitation of 60 ml. However, the summer weather had a high temperature, a high humidity of 75% and a significantly high precipitation of 790 ml. Even though the precipitation during the winter was much less than
the summer, the total wet deposition during the winter was much greater than the total wet deposition during the summer. From this fact, it is inferred that the total amount of wet deposition is highly dependent upon the emission strength of the sources and temperature, and might be also dependent on characteristics of the winds blowing from the sources rather than the amount of precipitation. An analysis of the total deposition of 16 PAHs deposited onto Ulsan Bay during the winter and the summer showed that 89.9% of the PAHs deposited had less than or equal to 4 aromatic rings; 2, 3 and 4 aromatic rings was 38.0%, 27.8% and 24.1%, respectively. Atmospheric deposition of the PAHs, having high molecular weight and low Henry’s law constant, on Ulsan Bay was much less than that of the PAHs with low molecular weight and high Henry’s law constant characteristics (Offenberg and Baker, 2002; Bamford et al., 1999; Park et al., 2001). Major components of the PAHs deposited onto Ulsan Bay consisted of naphthalene (2 rings) of 38.0%, acenaphthene (3 rings) of 13.1%, fluoranthene (4 rings) of 12.4% and pyrene (4 rings) of 10.3%, respectively. In particular, naphthalene was the most prominent bicyclic hydrocarbon form deposited onto Ulsan Bay during the winter and its wet deposition was more important than its dry deposition. The high water solubility of naphthalene due to high Henry’s law constant could increase its wet deposition during the winter (Mackay et al., 1992; Golomb et al., 1997a, b). However, high vapor pressure and short lifetime of naphthalene could contribute to its revolatilization and deterioration during the high temperature season, and thus they could be a cause of its lower
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deposition during the summer (Golomb et al., 1997a, b; Price et al., 2001).
5. Summary and conclusion An improved dry and wet collector system for the measurement of the atmospheric deposition of PAHs onto water surfaces has been successfully constructed. The building costs of the collector system are much lower than those of previous dry and wet collector systems. Evaporation of the surrogate solution in the dry collector was overcome by a constant supply of the surrogate solution. The formation of channels inside the wet adsorption cartridge was prevented by continuously providing water formed by a condensation of water vapor. The total amounts of PAHs deposited onto Ulsan Bay during the winter were much greater than during the summer. The increased emission sources of PAHs and lower temperature as well as the direction and distribution of the prevailing winds blowing from the sources could seriously increase the atmospheric deposition of PAHs onto Ulsan Bay during the winter. The PAHs deposited onto Ulsan Bay during the winter and the summer were mainly identified as dry deposition and wet deposition, respectively. 89.9% of the PAHs deposited onto Ulsan Bay had less than or equal to 4 aromatic rings; 2, 3 and 4 aromatic rings was 38.0%, 27.8% and 24.1%, respectively. Atmospheric deposition of the PAHs with high molecular weight and low Henry’s law constant was much less than those of the PAHs with low molecular weight and high Henry’s law constant.
Acknowledgements This study was supported by the Research Funds of the University of Ulsan. The authors wish to acknowledge the excellent assistance provided by Dr. Dan S. Golomb and George Fisher at the University of Massachusetts, Lowell, MA.
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