AEROSOL COMPOSITION CHANGE DUE TO DUST STORM: MEASUREMENTS BETWEEN 1992 AND 1999 AT GOSAN, KOREA

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1 AEROSOL COMPOSITION CHANGE DUE TO DUST STORM: MEASUREMENTS BETWEEN 1992 AND 1999 AT GOSAN, KOREA MIN HA PARK 1, YONG PYO KIM 1 and CHANG-HEE KANG 2 1 Department of Environmental Science and Engineering, Ewha Womans University, Daehyundong, Seodaemungu, Seoul, Korea; 2 Department of Chemistry, Cheju National University, 1 Aradong, Jeju, Korea ( author for correspondence, yong@ewha.ac.kr, Fax: ) (Received 8 May 2002; accepted 15 July 2002) Abstract. Aerosol composition change between dust storm and non dust storm periods is studied using the TSP (Total Suspended Particulate) data measured at Gosan, Korea between 1992 and The concentrations of elements measured between 1993 and 1996 and those of ions between 1992 and 1999 during dust storms are compared with those during non-dust storm periods in spring (March, April, and May). Among the analyzed ions, the concentrations of crustal species (potassium, calcium, magnesium, and chloride) and anthropogenic species (nitrate and non-sea salt (nss)-sulfate) increased when dust storm occurs while those of ammonium and sodium did not increase. Among the analyzed elements, the concentrations of crustal species (Fe, Al, Ca, Ti, and Zn) increased when dust storm occurs while those of anthropogenic species (Mn, V, Ni, Cu, Cd, and Cr) did not increase. The only anthropogenic element of which concentration increased during dust storm periods was Pb. It was found that the concentrations of nitrate and nss-sulfate were highest during spring. Also, the ratio of the yearly average concentrations of nitrate to nss-sulfate increases, probably due to the emission trend change in northeast Asia, especially, in China. Keywords: aerosol composition, dust storm, Gosan, long-term trend, N/S ratio 1. Introduction East Asia is characterized by both high anthropogenic and natural emissions of ambient trace species. For example, emissions of sulfur dioxide in Asia in 1990 were about 33.7 Tg, far higher value than that in the U.S.A. and Canada, about 2 Tg (Streets et al., 2000). Further, it is estimated that the emissions of major air pollutants such as sulfur dioxide, oxides of nitrogen, and carbon monoxide in China would increase between 1995 and 2020 (Streets and Waldhoff, 2000). Also, dust emissions from China become a serious concern due to its possible effects on both local and global environment (Chung, 1992). Thus, it is important to understand the effects of the emissions and transport of ambient trace species from East Asia, especially, China to the regional and global environment. Dust storm, also known as Yellow Sand phenomenon, is an important feature in northeast Asia. Dust particles can affect both regional and global environment such as visibility reduction, change of radiative forcing, and detrimental effects on human health. One concern, in particular, is that dust particles might react with Water, Air, and Soil Pollution: Focus 3: , Kluwer Academic Publishers. Printed in the Netherlands.

2 118 MINHAPARKETAL. Figure 1. Location of the measurement site and surrounding region. gaseous species during the transport and, thus, the properties of dust particles be changed (Nishikawa et al., 1991; Song and Carmichael, 2001a, b; Underwood et al., 2001). Jeju (formerly known as Cheju) Island is located at about 100 km south of Korean Peninsula and surrounded by the Asia continent, Korea, and Japan as shown in Figure 1. Jeju Island is considered as one of the cleanest areas in Korea with low emissions of air pollutants (Kim et al., 1998a). Thus, Jeju Island is an excellent location to study the transport and transformation of ambient trace species in East Asia and to study the impact of continental outflow. Gosan (formerly known as Kosan) is located on the far western edge of the island, the least developed area in the Island on the grounds of a meteorological station. Several intensive and routine measurement studies including PEM-West A and B and ACE-Asia have been carried out at Gosan (Carmichael et al., 1997; Chen et al., 1997; Kang et al., 2001; Kim et al., 1998a, b; Lee et al., 2001). One of the sampling programs is the measurement of total suspended particulates (TSP) started in March 1992 by using an automatic high volume tape sampler. In this work, the aerosol composition data measured at Jeju Island, Korea, between 1992 and 1999 were used to verify whether particle composition during dust storm is different from non dust storm periods. Also, temporal trend of the ob-

3 DUSTSTORMS AND AEROSOL COMPOSITIONS 119 served nitrate and sulfate concentrations, important acidic components of aerosols, are presented and discussed. 2. Measurement Data The measurement site is located on the western tip of Jeju Island ( E, N) as shown in Figure 1. A trailer containing the TSP sampler was situated about 10 m inside of the cliff, which is about 70 m above sea level. The sampling inlet is located about 6 m above the ground. Jeju upper-air meteorological station is located 100 m northeast of the site and measures upper-air meteorological parameters twice a day and other meteorological parameters. Particles were collected by a high volume tape sampler (Kimoto Electric Co., Model 195A), which is an automatic sampling system with roll type PTFE filters (Smitomo Electric, 100 mm 10 m). Particles were collected for either 6 or 2 hr and then a new clean filter surface was moved to the sampling area on which particles were collected. The flow rate was about 170 LPM. All the data presented in this work is 2 hr averaged results. The Teflon filters are divided into two sections; one part for elemental analysis and the other part for ion analysis. Inductively Coupled Plasma (ICP) Spectrophotometer (Jobin-Yvon Emission Instruments, Model JY 38S till 1997 and Thermo Jarrel Ash, Model Iris-duo from 1998) with a polychromator (PMT) detector was used for elemental analysis. Twelve elements (Cr, Ca, Zn, Cd, Ni, Fe, Al, Cu, Ti, Mn, Pb, and V) were analyzed. ion was analyzed by the indophenol method Eight ions were analyzed. NH + with a UV-Visible spectrophotometer (Kontron, Model Uvikon 860) and Na +,K +, Ca 2+,andMg 2+ by atomic absorption spectroscopy (GBC, Model Avanta-P). Anions, SO 2,NO 3,andCl were analyzed by ion chromatography (Dionex, Model DX-500). Non-sea salt (nss)-k +, nss-ca 2+, nss-mg 2+, and nss-so 2 concentrations are estimated by assuming all Na + are from sea salt and subtracting sea salt composition. Details on the ion analysis are given by Kim et al. (1998a). To ensure the quality of the data, two steps of quality control procedures were taken. First, instrument quality check had been carried out. Second, in addition to the sampling and analysis QA/QC, ion balance was used to check the validity of the data. The data with the ratio of the sum of the cation concentrations to the anion concentrations being within 30% are used for further data analysis. The criterion of 30% was chosen since organic ions and carbonates could be up to 30% of the total ion concentrations. Organic acids may be a major part of anions during summer when biogenic emissions of organic compounds are high and carbonates during spring when dust storms are frequent. But these were not analyzed. About 8% of the total data were discarded based on these two quality checks.

4 120 MINHAPARKETAL. Figure 2. Concentration ratios of elements between dust storm and non dust storm periods in spring measured at Gosan between 1993 and Results and Discussion 3.1. COMPOSITION CHANGE DURING DUST STORM The number of daily samples during dust storm and non dust storm periods in spring for the elements between 1993 and 1996 are 9 and 135, respectively. The numbers for the ions between 1992 and 1999 are 16 and 5, respectively. Figures 2 and 3 show the ratios of the concentrations of elements and ions during dust storm to those during non dust storm, respectively. Also, the concentrations of elements and ions at each period are shown in Tables I and II, respectively. In Figure 2 and Table I, it is evident that the concentrations of most elements during dust storm are higher than those during non-dust storm, especially crustal species such as Fe, Al, Ca, and Ti. Among ions, as shown in Figure 3 and Table II, the concentrations of most ions except NH + during dust storm were higher than non dust storm period. Especially, the concentrations of Ca 2+ during dust storm were higher than non dust storm period reflecting calcium is one of the major crustal species. Usually NH + is closely related with nss-so 2 in fine fraction of particles (Kim et al., 1998b). However, when gaseous sulfur species react on the surface of dust particles, nss- SO 2 is related with alkaline components of dust particles such as Ca 2+. Thus, in this case, nss-so 2 is not closely related with ammonium but with crustal species.

5 DUSTSTORMS AND AEROSOL COMPOSITIONS 121 Figure 3. Concentration ratios of ions between dust storm and non dust storm periods in spring measured at Gosan between 1992 and However, the concentrations difference alone is not sufficient to tell whether the particle composition is really changing during dust storm since the number of samples between dust storm and non dust storm are quite different, 9 vs. 135 for the case of elements and 16 vs. 5 for the case of ions. To further clarify the TABLE I Comparison of the element concentrations between dust storm period and non dust periods (unit: ng m 3 ) Fe Al Ca Zn Ti Mn Pb V Ni Cu Cd Cr Dust storm (N = 9) Mean S.D Non dust storm (N = 135) Mean S.D

6 122 MINHAPARKETAL. TABLE II Comparison of the ion concentrations between dust storm and non dust periods (unit: µg m 3 ) NH + Na + K + Ca 2+ Mg 2+ SO 2 NO 3 Cl nss- nss- nss- nss- K + Ca 2+ Mg 2+ SO 2 Dust storm (N = 16) Mean S.D Non dust storm (N = 5) Mean S.D TABLE III Element and ion species that are statistically higher during dust storm than non dust storm period Higher Not higher Elements Fe,Al,Ca,Zn,Ti,Pb Mn,V,Ni,Cu,Cd,Cr Ions K +,Ca 2+,Mg 2+, NH +,Na+ NO 3,Cl,SO 2, nss-so 2 concentration differences, it is necessary to carry out two-step statistical analysis; (1) F-test to check whether the distributions are homogeneous or heterogeneous and (2) t-test based on the homogeneity of the distributions (Yates et al., 1998). The F-test and t-test results with 95% confidence level are shown in Table III. During dust storm, the concentrations of crustal elements such as Al, Fe, Ca, Zn, and Ti were higher than non dust storm period while the concentrations of most anthropogenic elements such as Mn, V, Ni, Cu, Cd, and Cr were statistically not higher during dust storm period. The only anthropogenic element of which concentration was higher during dust storm was Pb. In addition, during dust storm, the concentrations of ions related with crustal origin such as K +,Ca 2+,andMg 2+ were higher during dust storm period. Among ions with the anthropogenic origin, the concentrations of SO 2 were higher during dust storm period. It is not clear whether Cl was crustal derived or not at this stage.

7 DUSTSTORMS AND AEROSOL COMPOSITIONS 123 Figure. Variation of the monthly mean concentrations of nss-sulfate measured at Gosan between 1992 and Figure 5. Variation of the monthly mean concentrations of nitrate measured at Gosan between 1992 and 1999.

8 12 MINHAPARKETAL. Figure 6. Variation of the yearly mean nss-sulfate concentrations measured at Gosan between 1992 and It has been observed by several studies that NO 3 is closely related with Ca2+ rather than NH + or SO2 in Gosan (Chen et al., 1997; Kang et al., 2001; Kim et al., 1998a; Lee et al., 2001). It was postulated that surface reactions of the oxides of nitrogen including HNO 3 on dust particles might be the main reason for that (Song and Carmichael, 2001a, b; Underwood et al., 2001). Thus, the higher concentration of NO 3 during dust storm is probably due to the interactions between gaseous oxides of nitrogen and dust particles. Nishikawa et al. (1991) measured particle size distributions and their ionic and elemental concentrations in a marine area in Japan between 1987 and They found that during dust storm, the concentrations of nss-so 2 in coarse mode particles increased. They postulated that interactions between gaseous acidic species and dust particles cause the increase of nss-so 2 in coarse mode particles. However, based on the single particle analysis results in Beijing between 1995 and 1996, Zhang and Iwasaka (1999) suggested that almost no SO 2 is formed is hardly formed on the surface of dust particles over Beijing. Thus, it is probable that the observed higher concentrations of SO 2 during dust storm at Gosan are processed during the transport over the Yellow Sea.

9 DUSTSTORMS AND AEROSOL COMPOSITIONS 125 Figure 7. Variation of the yearly mean nitrate concentrations measured at Gosan between 1992 and TREND OF NSS-SULFATE AND NITRATE To further study the higher concentrations of SO 2 during dust storm, the monthly average concentrations of nss-so 2 were studied as shown in Figures and 5, respectively. Both species show the maximum concentrations during spring, March and April when dust storms are most frequent. Both species show minimum concentrations during summer when the precipitations amount is the highest and wind blows mostly from the Pacific. Thus, dust storm may play a role in the elevated nss-so 2 during spring at Gosan. In Figures 6 and 7, the yearly average concentrations of nss-so 2 are shown, respectively. The concentration of nss-so 2 is stable between 1992 and 1999 while that of NO 3 is slightly increasing. The mole ratio of nitrate to nss- SO 2 is shown in Figure 8. It is evident that the ratio is increasing. This trend of relative increase of NO 3 compared to nss-so2 is also observed in the rain samples collected in western Japan between 1987 and 1996 (Takahashi and Fujita, 2000). Also shown in Figure 8 is the mole nitrogen to sulfur ratios estimated from the emission data of SO 2 and NO 2 at Jeju Island (MOE, 2000), Korea (MOE, 2000), and China (Kim, 1999; Streets and Waldhoff, 2000), respectively. Even though there are several limitations in directly comparing emission data and measurement

10 126 MINHAPARKETAL. Figure 8. Variation of the ratio of the yearly mean concentration of nitrate to nss-sulfate measured at Gosan between 1992 and 1999 along with the ratios estimated from the emission data at Jeju Island, Korea, and China. Emission data for Jeju Island and Korea are from MOE (2000) and for China are from Kim (1999) and Streets and Waldhoff (2000). data, it is reasonable that the observed ratio values at Gosan are indicative of emissions in China. Thus, this trend suggests the change of emission pattern in the region, especially, in China.. Summary Dust storms in northeast Asia becomes a serious concern in the region and in the world due to the huge amount of emitted dust particles and their effects on both regional and global environmental problems. Aerosol composition change between dust storm and non dust storm periods is studied using the TSP data measured at Gosan, Korea between 1992 and The concentrations of elements between 1993 and 1996 and those of ions between 1992 and 1999 during dust storms are compared with those during non-dust storm periods in spring (March, April, and May). During dust storm period, the concentrations of elements and ions with natural origin increased. Further, among the anthropogenic species, the concentrations of lead (Pb), non-sea salt sulfate (nss-so 2 ), and nitrate (NO 3 )werealso

11 DUSTSTORMS AND AEROSOL COMPOSITIONS 127 higher during dust storm period. Increase of the concentrations of nss-so 2 and NO 3 during dust storm suggests possibility of interactions between acidic gaseous species and dust particles. Based on the aerosol data measured at Gosan, Korea between 1992 and 1999, it was found that (1) the concentrations of NO 3 and nss-so2 are highest during spring and (2) the ratio of NO 3 to nss-so2 increase probably due to the emission trend change in northeast Asia, especially, in China. Acknowledgement This work was carried out with the support from the Climate Environment System Research Center a SRC program funded by the Korea Science and Engineering Foundation, the Meteorological Research Institute Korea, and the Ministry of Environment Korea. References Carmichael, G. R., Hong, M.-S., Ueda, H., Chen, L.-L., Murano, K., Park, J. K, Lee, H., Kim, Y., Kang, C. and Shim, S.: 1997, Aerosol composition at Cheju Island, Korea, J. Geophys. Res. 102, Chen, L.-L., Carmichael, G. R., Hong, M.-S., Ueda, H., Shim, S., Song, C. H., Kim, Y. P., Arimoto, R., Prospero, J., Savoie, D., Murano, K., Park, J. K., Lee, H.-G. and Kang, C.: 1997, Influence of continental outflow events on the aerosol composition at Cheju Island, South Korea, J. Geophys. Res. 102, Chung, Y.-S.: 1992, On the observations of Yellow Sand (Dust Storms) in Korea, Atmosph. Environ. 26A, Kang, C.-H., Kim, W.-H., Hu, C.-G., Kim, Y.-P., Shim, S.-G. and Hong, M.-S.: 2001, Composition Analysis and Characteristics of Aerosols Collected at Kosan Site in Cheju Island, Korea during , Presented at the 12th World Clean Air and Environment Congress and Exhibition, Seoul, Korea, K-0099, Kim, Y. P.: 1999, Air quality in northeast Asia with emphasis on China, J. Korean Soc. Atmosph. Environ. 15, (in Korean). Kim, Y. P., Shim S.-G. and Moon, K. C.: 1998a, Monitoring of air pollutants at Kosan, Cheju Island, Korea, during March April 199, J. Appl. Meteorol. 37, Kim, Y. P., Lee, J. H., Baik, N. J., Kim, J. Y., Shim, S.-G. and Kang, C.-H.: 1998b, Summertime characteristics of aerosol composition at Cheju Island, Korea,Atmosph. Environ. 32, Lee, J. H., Kim, Y. P., Moon, K.-C., Kim, H.-K. and Lee, J. B.: 2001, Fine particles measurement at two background sites in Korea between 1996 and 1997, Atmosph. Environ. 35, MOE, Ministry of Environment, Korea: 2000, Environment Yearbook, Seoul, Korea (in Korean). Nishikawa, M., Kanamori, S., Kanamori, N. and Mizoguchi, T.: 1991, Kosa aerosol as aeolian carrier of anthropogenic material, Sci. Total Environ. 107, Song, C. H. and Carmichael, G. R.: 2001a, A three-dimensional modeling investigation of the evolution processes of dust and sea-salt particles in east Asia, J. Geophys. Res. 106, Song, C. H. and Carmichael, G. R.: 2001b, Gas-particle partitioning of nitric acid modulated by alkaline aerosol, J. Atmosph. Chem. 0, 1 22.

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