- Email: [email protected]
Chemical characteristics of long-range transport aerosol at background sites in Korea
Atmospheric Environment 43 (2009) 5556–5566
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Chemical characteristics of long-range transport aerosol at background sites in Korea Yoo Jung Kim a, Jung-Hun Woo b, Young-Il Ma a, Suhyang Kim b, Jung Sik Nam a, Hakyoung Sung b, Ki-Chul Choi b, Jihyun Seo a, Jeong Su Kim c, Chang-Hee Kang d, Gangwoong Lee e, Chul-Un Ro f, Duk Chang a, Young Sunwoo b, * a
Department of Environmental Engineering, Konkuk University, Seoul, Republic of Korea Department of Advanced Technology Fusion, Konkuk University, Seoul, Republic of Korea Global Environment Research Center, National Institute of Environmental Research, Incheon, Republic of Korea d Department of Chemistry, Cheju National University, Jeju, Republic of Korea e Department of Environmental Science, Hankuk University of Foreign Studies, Youngin, Republic of Korea f Department of Chemistry, Inha University, Incheon, Republic of Korea b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 July 2008 Received in revised form 28 March 2009 Accepted 31 March 2009
In this study, background concentration sites of Deokjeok and Gosan, which were deemed suitable for monitoring the impact of long-range transported air pollutants, were selected. An investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at both sites using appropriate methodologies to make initial estimations was conducted. Episodic measurements of PM2.5, PM10, and size distribution, along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. As for frequency of wind direction, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. For PM2.5 and PM10, the mass concentrations from north and east China were higher than other cases, originating from the ocean. In the northerly-wind case, meteorological properties for Deokjeok and Gosan and the influence of carbon emissions from northwest Korea resulted in a changing of air mass properties during transport. As was the case with mass concentration, the highest contribution for ionic and carbon components of PM2.5 and PM10 for both sites appeared for the westerly wind case. A specially high relative contribution, greater than 1.4 times, was apparent in the secondary aerosol case because of a large influence of long-range transported pollutants from east China. Carbon components exhibited different behaviors for the northerly and westerly wind cases compared with secondary aerosol. The major reason for this discrepancy appears to be the carbon emissions from northwest Korea. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
Keywords: Aerosol Background concentration Long-range transport East Asia
1. Introduction The long-range transport of air pollutants in Northeast Asia is a very relevant current issue. Northeast Asia suffers from mass emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from China (Streets et al., 2001). In recent years, the annual growth rate of nitrogen dioxide (NO2) concentration over the industrial areas in China has significantly increased, as high as about 50% during 1996–2004(Richter et al., 2005). The Korean Peninsula is located on the eastern edge of the continent of Asia and lies in a belt of prevailing westerlies
* Corresponding author. Tel.: þ82 2 450 3541; fax: þ82 2 453 2706. E-mail address: [email protected] (Y. Sunwoo).
accompanying seasonally changing centers of atmospheric presng peninsula sure. The distance between Seoul in Korea and Sh ando in China is approximately 400 km. Therefore, the impacts of longrange transport of pollutant emissions from the industrial centers of eastern China and uplifted dust particles from the relatively dry regions further inland are quite severe (Lee et al., 2001; Davis and Jixiang, 2000). Therefore, much research has been performed and reported for the background atmospheric monitoring of long-range transport air pollutants in Korea. However, multiple background monitoring sites are needed for the analysis of the impact of rapidly increasing long-range transported air pollutants such as SO2, NOx, and particles, and a large volume of data should be collected for construction of a reliable database for the major pollutants. Thus, we have selected suitable background concentration sites for monitoring
1352-2310/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.03.062
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
the impact of long-range transported air pollutants, and conducted an investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at the sites using appropriate methodologies to make initial estimations. 2. Monitoring and analysis methodology 2.1. Study location and monitoring data After a long-term survey for finding the proper background concentration sites suitable for monitoring the impact of longrange transport of air pollutants, the monitoring sites of Deokjeok and Gosan were selected in this study. Both sites are located along the western coast of Korea, close to the eastern coast of China. Deokjeok (37130 N, 126 90 E) is located to the west of the Korean Peninsula, and Gosan (33170 N, 126100 E) is situated on the west coast of Jeju Island off the southern tip of the Korean Peninsula as illustrated in Fig. 1. Both sites are located on islands and there are no large anthropogenic sources adjacent to the sites. The island of Deokjeok covers 20.9 km2 and there are no industrial facilities, little transportation and a population of one thousand. Forests and fields cover almost 90% of the area. Passenger ships shuttle only 3–4 times everyday and there is little other traffic. Emissions per unit area and population density for Ongjin county which contain many islands including Deokjeok, were low relative to near by neighboring counties. Aerosol concentration levels for Deokjeok were also relatively lower than those for national background monitoring sites, Gangwha and Taean, on the west coastal region (Lee ndo ng peninsula, including one et al., 2002). On a regional scale, Sha of the biggest industrial complexes in China, is located merely 330 km to the west of Deokjeok. Incheon city, in Korea, is located 70 km to the east. Deokjeok was the farthest island from the Korean
5557
Peninsula in the ‘‘West Sea’’, where electric power was available to run experimental equipments. The Gosan site is considered an ideal location to monitor background atmospheric concentrations in the northeast Asia region. The Korean mainland and Shanghai, in China, are located over 100 km and 500 km away, respectively. There are no large local industrial sources. This site is located on the west edge of Jeju island. Gosan was a super site during the ACE-Asia project (Alfaro et al., 2003) and many experiments were performed at this location. So, Deokjeok and Gosan satisfy most of the conditions for monitoring background air quality. Episodic measurements of PM2.5, PM10, and size distribution along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. The sampling was carried out over a total of 91 days divided into 8 periods as follows: October 15–24 in 2005, January 5–19, April 1–15, June 6–15, October 15–25 in 2006 and January 11–20, April 16–25, July 16–25 in 2007. Teflon filter packs connected to cyclones (URG, 16.7 L min1) with cut-off diameters of 2.5 mm and 10 mm were used for measurement of PM2.5 and PM10. We used a MOUDI (Micro-Orifice Uniform Deposit Impactors; MSP, Model 100 with rotator-8 stage or without rotator-10 stage) for size distribution with 30 L min1 flow late. The MOUDI is comprised of 8 stages with cut-off diameters of 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, and 0.18 mm, respectively. Additional cut-off points at 0.1 and 0.056 mm are provided with the 10 stage model. The Teflon filters (Gelman Sciences, pore size 2.0 mm, 47 m ø) and quartz filters (Whatman, 47 mm ø) were exchanged at 9 am everyday. Size distribution sampling was carried out every 2–4 days for two samples per sampling period. Mass and ionic concentrations were measured using teflon filters. Carbon components were captured utilizing baked quartz filters. Mass concentration was measured using gravimetric analysis for PM2.5, PM10, and size
Fig. 1. Location of background monitoring sites.
5558
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
þ þ 2þ 2þ distribution. Ionic components, such as NHþ 4 , Na , K , Ca , Mg , , NO and Cl , of particles were analysed by the Ion ChromaSO2 4 3 tography method (Dionex, ICS-2000). Carbon components including elemental carbon and organic carbon of PM2.5 were analysed using the TOT (Thermal Optical Transmittance) method.
2.2. Back trajectory analysis Lagrangian trajectories were used to identify the pathways of the air mass transport for estimation of source–receptor relationships of the air pollutants. The trajectories reflect the large-scale atmospheric transport characteristics of air masses to the sampling sites. The trajectories were estimated using the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model with integrated data for hemispheric upper air. Back trajectory analysis provides a better understanding of air flow and long-range transport patterns. We analysed the aerosol characteristics with respect to categorized back trajectories for initial estimation of source location and quantitative contribution. 72-h back trajectories were calculated using the HYSPLIT model from NOAA (NOAA/ARL, 2007; Draxler, 1996; Draxler and Hees, 1997, 1998) with an endpoint height of 500 m. Input data for HYSPLIT utilized the framework of FNL (Final Run) meteorological
data which are 6-hourly archived data from GDAS (Global Data Assimilation System) of NCEP (National Centers for Environmental Prediction). In this study, the modeling was performed for GMT from 0 to 24 to correspond with the local time of 9 am for filter change at the sampling site. Polissar et al. (1998) suggested the endpoint height of 500 m for looking at patterns in the wind field of air masses at 100–600 m height to define the source locations and long-rage transport patterns in Barrow, Alaska. The value of this height to represent average PBL (Planetary Boundary Level) was widely used by many researchers (Fan et al., 1995; Gao et al., 1993; Hafner and Hites, 2003; Hsu et al., 2003; Begum et al., 2005; Poissant and Pilote, 1998; Polissar et al., 1998). 72 h were adequate for most trajectories, passing through major source regions like Fig. 2. Hwang and Ro (2005), Lee et al. (2006, 2008) used 72-h back trajectories to identify air mass pathways. We categorized the trajectories into 5 sectors according to the air mass pathways as follows. The air masses originating from the Chinese or Russian continent without passing any major water body (thus having to come from the north direction for the above monitoring sites) were categorized as sector 1. Those coming from the Chinese continent and passing the ‘‘West Sea’’ and entering the peninsula through the west coast of Korea were denoted as sector 2. Those originating from the oceans without having passed through
Fig. 2. Examples of 72-h back trajectories for the four sectors.
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
China were categorized as sector 3. These air masses mostly came from the south. Those originating from China or Russia and entering the peninsula through the east coast of Korea were designated as sector 4. Finally, the air masses moving much slower than that of other sectors or spinning around the measurement sites were categorized as sector 5. The trajectories in sector 5 lay near the sampling sites for an extended period of time. Representative examples of the 5 sectors, as mentioned above, are shown in Fig. 2. 2.3. Single particle analysis Single particle analysis was also performed to evaluate the types and the quantitative characteristics of individual aerosols for the summer, 2007 data. A single particle analysis technique, low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA), was applied to characterize the aerosol samples collected at Deokjeok for 3 days on July 20, 22, and 23 in 2007. We sampled twice, at 10 am and 6 pm. Particles were collected on aluminum foil using a three-stage cascade impactor sampler (Dekati, PM10 Impactor). This impactor, with a sampling flow rate of 10 L min1, has aerodynamic cut-off diameters of 10, 2.5, and 1 mm in stages #1–3, respectively. Particles larger than the size of 10 mm are collected at the first stage of the impactor, while the size of collected particles are in the range of 10–2.5 mm in stage 2 and 2.5–1 mm in stage 3, respectively. The quantitative determination of concentrations of low-Z elements such as C, N, and O in individual particles was carried out by low-Z particle EPMA using an X-ray detector equipped with an ultra-thin window (Hwang and Ro, 2006; Ro et al., 2005). 2.4. Emissions in Northeast Asia We analysed the results of an Asian emissions inventory from the INTEX-B project (NASA, 2006) to understand more precisely the aerosol characteristics and their sources. This emission inventory was prepared by Qiang Zhang and David G. Streets, Decision and Information Sciences Division, Argonne National Laboratory, for the INTEX-B project of the National Aeronautics and Space Administration (NASA). This inventory includes the emissions of SO2, NOx, CO, VOC, PM10, PM2.5, BC, and OC by sector (power, industry, residential, and transportation) and six speciated VOCs by sector files. This data set is only for anthropogenic emissions in 2006 and the resolution of this inventory is 0.5 degrees. The INTEX-B is one of many experiments that aim to understand the transport and transformation of gases and aerosols on transcontinental/intercontinental scales and assess their impacts on air quality and climate. The INTEX-B was carried out in the spring of 2006.
(Perry et al., 1999), and compared to natural background data of Europe, by about 3–5 mg m3 for PM2.5 and 5–8 mg m3 for PM10 (Putaud et al., 2004). The correlation between the two sites was not high, because each site has differing local meteorological properties and different episodic periods because a distance of approximately 400 km separates the two sites even though they almost have the same longitude. High PM2.5 to PM10 ratios of 78.6% for Deokjeok and 77.3% for Gosan, were prevalent, and the ratio for Deokjeok was similar to that of Gosan. The major ionic components in PM2.5 and PM10 were SO2 4 , NO3 , for both sites (Table 1). Carbon is also a major component and NHþ 4 in PM2.5 and OC has a higher concentration than EC. For all cases, þ SO2 4 showed the highest concentration, with OC, NH4 , NO3 and EC in decreasing order. The concentrations of other ionic components have relatively large differences. High contributions of secondary pollutants (33.5–43.7%) and carbon (18.9–19.9%) aerosol showed the influence of anthropogenic sources. Carbon aerosol in PM10 and some other major components, including metals and elemental S in PM2.5, were not analysed. This is likely a major reason for the relatively high unknown contribution. 3.2. Sector frequency and meteorological property Table 2 shows the relative frequency and local meteorological properties from AWS (Auto Weather System) data of categorized air masses. The travel path was categorized according to sectors at Deokjeok and Gosan as mentioned previously. We performed back trajectory analyses except for the 13 non-categorized cases (14.3%) for Deokjeok and 16 days (17.6%) for Gosan where the trajectories moved through more than two sectors in one day. A frequency of 33.0% for sector 1, originating from the north, was the highest for Deokjeok, and that of sector 2, originating from the west, was 27.5%. For Gosan, frequencies of 22.0% and 31.9% were obtained for sectors 1 and 2, respectively. The sum of air masses from sectors 1 and 2 made up 60.5% and 53.9% for Deokjeok and Gosan, respectively. Meanwhile, both sites had lower frequencies for sector 3 from the south and sector 4 from the east. In case of
Table 1 Aerosol concentration and contribution. PM10
PM2.5 Mean
SD
Contribution
Mean
SD
Contribution
32.8 6.0 2.4 2.6 0.3 0.1 0.4 0.4 0.2
33.8 5.9 2.4 1.9 0.3 0.1 0.3 0.4 0.2
100.0% 18.2% 7.3% 8.0% 1.0% 0.3% 1.1% 1.1% 0.7%
12.0 4.7 1.4 1.6 0.2 0.04 0.2 0.3 0.3
100.0% 26.8% 6.5% 10.4% 1.1% 0.3% 1.2% 1.9% 1.2%
Deokjeok
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl OC EC Unknown
25.7 5.4 1.7 2.3 0.2 0.1 0.3 0.2 0.2 3.8 1.0 10.5
23.0 5.6 2.0 1.8 0.2 0.05 0.3 0.2 0.2 2.1 0.5
100.0% 20.9% 6.7% 9.0% 0.8% 0.2% 1.1% 0.8% 0.6% 15.0% 3.9% 41.0%
Gosan
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl OC EC Unknown
17.6 4.8 1.0 1.9 0.2 0.04 0.2 0.3 0.2 2.7 0.8 5.6
11.2 4.4 1.0 1.5 0.1 0.03 0.2 0.2 0.2 1.7 0.5
100.0% 27.0% 5.7% 10.8% 0.9% 0.2% 1.2% 1.6% 1.1% 15.5% 4.4% 31.7%
3. Results and discussion 3.1. Overall aerosol characteristics The averages and standard deviations of PM2.5 and PM10 mass concentrations for Deokjeok were higher than that of Gosan. PM2.5 mass concentrations for Deokjeok and Gosan during the overall sampling period were 25.3 22.6 and 17.2 10.8 mg m3, respectively. PM10 mass concentrations for Deokjeok and Gosan were 32.2 32.7 mg m3 and 22.3 11.6 mg m3, respectively. The daily variations of both sites were quite similar. This aerosol concentration level represents typical regional characteristics in Northeast Asia. This level is relatively higher than global background data, by about 1 mg m3 for PM2.5 than at Mauna Loa, Hawaii
5559
20.5 22.3 6.0 1.4 2.3 0.2 0.1 0.3 0.4 0.3
11.3
57.4%
50.6%
5560
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
Table 2 Sector frequency and meteorology properties.
Deokjeok
Frequency Temperature Relative Humidity Wind Speed Precipitation day Precipitation contribution Precipitation Averagea
Gosan
Frequency Temperature Relative Humidity Wind Speed Precipitation day Precipitation contribution Precipitation Averagea
a
Sector 1
Sector 2
Sector 3
Sector 4
Sector 5
30 days 33.0% 4.4 C 58.6% 3.4 m s1 4 days 13.3% 0.7 mm day1
25 days 27.5% 13.4 C 70.2% 4.0 m s1 3 days 12.0% 1.1 mm day1
8 days 8.8% 19.0 C 89.7% 3.6 m s1 5 days 62.5% 12.6 mm day1
10 days 11.0% 11.9 C 61.7% 3.3 m s1 1 day 10.0% 0.8 mm day1
5 days 5.5% 14.1 C 76.6% 5.9 m s1 2 days 40.0% 3.9 mm day1
20 days 22.0% 11.4 C 67.7% 7.7 m s1 4 days 20.0% 1.3 mm day1
29 days 31.9% 14.7 C 68.0% 6.8 m s1 6 days 20.7% 0.9 mm day1
13 days 14.3% 18.8 C 85.9% 8.9 m s1 9 days 69.2% 12.2 mm day1
8 days 8.8% 15.6 C 64.5% 4.9 m s1 1 day 12.5% 0.01 mm day1
5 days 5.5% 13.7 C 76.7% 4.8 m s1 1 day 20% 1.4 mm day1
Precipitation average ¼ overall precipitation for each sector/frequency day for each sector.
sector 5, where the air masses are moving slower than that of other sectors or spinning around the sites, impact was minimal relative to other sectors due to a relatively low concentration of 5.5% at both sites. Thus, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. This result reflects the general wind pattern in the Korean Peninsula. Kim et al. (2007) identified the transport pattern of about 35% originating from Central-Southern China and Northern China-Mongolia from March 2003 to February 2005. He et al. (2003) performed cluster analysis with back trajectories from March 1998 to July 1999, and reported that a group of trajectories ndo ng peninsula and ‘‘West Sea’’ made through Northern China, Sha up 70% and another group, about 28%, through Russia, Mongolia and Northeastern China. Meteorological characteristics appear significant for some cases. In particular, sector 1 for Deokjeok characteristically had cold and relatively dry air masses. An average temperature of 4.4 C and a relative humidity of 58.6% for Deokjeok showed lower temperatures compared with other sectors in the range of 11.9–19.0 C. However, air masses of sector 1 for Gosan had a quite different behavior. Although the relative humidity (67.7%) was similar with other sectors, the temperature (11.4 C) was only slightly lower than that of other sectors. The differences of temperature and relative humidity between Deokjeok and Gosan for sector 1 were 7.0 C and 9.1%, respectively. It should be noted that air masses having pathways from the north were most likely heated and supplied with vapor while passing across the section between Deokjeok and Gosan. Thus, we looked closely at back trajectories for sector 1 on similar days in winter to find detailed reasons for the difference, and 9 days were selected. The differences of temperature and relative humidity between Deokjeok and Gosan at the conditions as referred to above were quite similar. An average temperature of 1.6 C and a relative humidity of 53.6% were obtained for Deokjeok while the temperature and relative humidity for Gosan were 6.2 C and 65.0%, respectively. The vertical profile for sector 1 showed that the altitude of air masses dropped near Deokjeok and went on to Gosan maintaining low altitude. For sector 3, air masses with precipitation appeared frequently and the relative humidity was about 70% for both sites. Average precipitation signifies overall precipitation divided by total days for each sector. It was 12.6 mm day1 and 12.2 mm day1 for Deokjeok and Gosan, respectively, and is quite unique compared to other sectors. The highest relatively humidity of about 90% and a temperature of 19 C compared with other sectors were seen in
this sector. For sector 3, all days, except just one day in summer for Deokjeok, were selected as experimental days, while similar contributions were seen in spring and summer for Gosan. It is believed that hot and damp air masses were heavily influenced by tropical cyclones. For sector 5, different behaviors were seen for Deokjeok and Gosan. The two sites did not overlap for the same days in sector 5. Back trajectories of Deokjeok showed air masses moving slower than that of other sectors or spinning around the sites. By applying back trajectories extending back 120 hours, however, it could be seen that the sector 5 air masses of Gosan moved slowly through the Korean Peninsula and originated from east China.
3.3. Aerosol characteristics The individual average concentration level for each sector was considered by the contribution ratio of each sector average versus the overall average.
Relative contribution ¼
sector average conc: overall average conc:
Overall average, as mentioned above, does not mean 91 days but actual experimental days of 78 and 75 days for Deokjeok and Gosan, respectively, excluding non-categorized cases. We also classified the sectors into 1–4 and 5 for the detailed analysis of aerosol characteristics in this study, because sectors 1–4 represented long-range transported air masses. Table 3 shows relative contributions of mass and chemical components of each sector for both sites, especially PM2.5 and PM10. For all cases, the mass concentration from sector 2 had the highest contribution 120%, compared to the overall average. The relative contributions for sectors 1 and 2 from north and east China were also higher, while sectors 3 and 4, originating from the oceans showed lower contributions. However, the relative contributions for sectors 1 and 2 showed different characteristics between Deokjeok and Gosan. The relative contribution for sector 1 for Gosan was below 1, whereas that of PM2.5 (1.38) and PM10 (1.33) dominated sector 2. For Deokjeok, the relative contribution for sector 2 was slightly lower than Gosan, and a higher value of about 1.1 appeared for sector 1. It seems that different patterns for sector 1 are caused by the differing relative distances between the two measuring sites and north China which includes the northeast industrial complexes. It also seems that the difference between meteorological properties such as
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
5561
Table 3 Sector relative contribution of mass and chemical components. Deokjeok
Gosan
Sector 1
Sector 2
Sector 3
Sector 4
Sector5
Sector1
Sector2
Sector3
Sector4
Sector5
PM2.5
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl OC EC
1.05 0.74 0.72 0.79 0.86 0.91 0.74 0.67 0.84 1.14 1.10
1.31 1.55 1.71 1.44 1.37 1.27 1.61 1.40 1.22 1.10 1.18
0.67 1.18 0.39 1.02 1.24 1.33 0.86 1.28 1.50 0.76 0.58
0.50 0.33 0.58 0.48 0.50 0.60 0.47 0.99 0.85 0.72 0.76
0.72 0.92 0.86 1.11 0.64 0.34 0.60 0.64 0.58 0.58 0.65
0.85 0.69 0.93 0.70 1.00 1.14 0.80 0.83 1.03 0.98 0.96
1.38 1.47 1.41 1.43 1.23 1.03 1.52 0.89 0.76 1.30 1.29
0.42 0.52 0.25 0.57 0.67 0.78 0.45 1.20 1.06 0.38 0.55
0.60 0.29 0.58 0.35 0.57 1.06 0.20 1.41 1.86 0.72 0.65
1.56 1.92 1.52 1.87 1.26 0.72 1.39 1.17 0.75 1.30 1.15
PM10
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl
1.11 0.77 0.87 0.84 0.92 0.85 0.83 0.87 0.73
1.22 1.53 1.47 1.40 1.21 1.29 1.49 1.25 1.28
0.66 1.06 0.30 0.94 1.33 1.24 0.68 0.77 1.28
0.53 0.33 0.66 0.48 0.60 0.70 0.62 1.06 1.00
0.71 1.01 1.26 1.12 0.76 0.73 0.64 0.74 0.81
0.86 0.74 0.91 0.76 1.27 1.10 0.86 0.82 1.07
1.33 1.43 1.42 1.39 1.06 1.01 1.51 0.98 0.73
0.48 0.49 0.27 0.51 0.64 0.85 0.36 1.11 1.16
0.65 0.40 0.58 0.49 0.53 0.92 0.27 1.29 1.58
1.56 1.82 1.51 1.83 1.24 1.09 1.27 1.12 0.92
temperature and relative humidity for sector 1 between Deokjeok and Gosan occurs due to changing air mass properties during transport. The contributions were the highest for sector 2 and lowest for sectors 3 and 4 for both sites. This indicates that influences by the continent far outweigh those from local urban sources for these two sites. Sector 5 for Deokjeok showed a relatively lower contribution of about 0.7, but the contribution for Gosan was very high, over 1.5. In some episodic cases, air masses for sector 5 for Gosan moved slowly through Korea and east China. It seemed that the major cause of these episodic cases was the effect of air pollutants accumulating in slow-moving air masses. However, we could not clearly identify the major source location, east China or South Korea. More case studies for sector 5 will be needed to verify this. As with mass concentration, the highest contribution for almost all ionic and carbon components of PM2.5 and PM10 for both sites appeared for sector 2. In particular, a high relative contribution of above 1.4 was seen in the secondary aerosol case. In any case, the
relative contribution of secondary aerosol for sector 2 is higher than that of mass contribution. It seems that a primary reason is large emission of SO2, NOx, and NH3 from industrial complexes in the east coast of China. Relatively large emission sources of NH3, SO2 and NOx are located in the east coast of China, as illustrated in Fig. 3, based on the Asian emissions inventory dataset developed in support of the INTEX-B project (NASA, 2006) and other preceeding results on emissions (Woo et al., 2003). It takes approximately 2–4 days for gaseous precursors to þ transform in the atmosphere to particulate SO2 4 , NH4 , and NO3 . Air mass trajectories from the west appeared frequently, as mentioned previously, and it took about 3 days for the transport of air masses from east China to both sites. Therefore, it is reasonable to think that much of the secondary aerosol originated from east China. The sum of relative contribution for secondary aerosol such as SO2 4 , NHþ 4 , and NO3 in PM2.5 and PM10 is about 40% for sector 2. So, it appears that there is a large influence of long-range transported pollutants from China.
Fig. 3. The Asian emissions inventory dataset for SO2 and NOx (unit: metric tons year1 0.5 cell1) (Reference: This Asia inventory dataset is developed in support of NASA’s INTEX-B mission (2006)).
5562
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
Table 4 Sector equivalent ratio. Sector 1
Sector 2
Sector 3
Sector 4
Sector 5
PM2.5
PM10
PM2.5
PM10
PM2.5
PM10
PM2.5
PM10
PM2.5
PM10
Deokjeok
2 NHþ 4 /(SO4 ) 2 /(SO NHþ 4 4 þ NO3 )
1.24 0.99
1.28 0.95
0.97 0.75
1.07 0.83
0.99 0.92
1.02 0.93
1.71 1.17
1.68 1.05
1.38 1.12
1.28 0.93
Gosan
2 NHþ 4 /(SO4 ) 2 NHþ 4 /(SO4 þ NO3 )
1.10 0.90
1.08 0.87
1.06 0.91
1.02 0.87
1.17 1.08
1.13 1.00
1.31 0.98
1.01 0.85
1.05 0.93
1.06 0.91
The concentration and relative contribution of SO2 4 had the highest value for every sector at both sites. The concentration and increased in proportion to temperature, contribution of SO2 4 especially for sector 2 and the summer season. The winter/summer concentration ratio of SO2 4 for PM2.5 was 25.0% and for PM10 32.8% at Deokjeok, and 53.3% for PM2.5 and 63.9% for PM10 at Gosan. The temperature differences between summer and winter were 22.3 C for Deokjeok and 10.8 C for Gosan. Thus, we could surmise that the concentration was largely influenced by photochemical SO2 4 reaction at high temperature and large SO2 emissions in east China. Concentrations of NHþ 4 appear to be influenced by emissions from anthropogenic sources rather than biogenic sources. In the
2 clear ocean region, NHþ 4 does not neutralize SO4 due to lower NH3 þ concentrations (Covert et al., 1998). The NH4 /SO2 4 equivalent ratio was suggested to be about 0.65 in the clean Pacific ocean (Quinn et al., 1990). When the condition for neutralization is sufficient, that 2 is, when the reacted NHþ 4 to SO4 ratio is above 1:1, then this is good evidence of local NH3 sources. Then the NHþ 4 is converted from NH3 during long-range transport (Song and Carmichael, 2 1999). The NHþ 4 /SO4 equivalent ratios of PM2.5 and PM10 were both above 1.1 for both sites regardless of the sectors for the overall experimental period (Table 4). The ratios are above 1.0 for every sector except PM2.5 for sectors 2 and 3 at Deokjeok. Although these ratios were below 1.0, they were 0.97 and 0.99 for each sector,
Fig. 4. Secondary aerosol size distribution.
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
respectively. We tentatively concluded that the continental influence by far outweigh those from local NH3 sources for NHþ 4 , because both sites are located in relatively clean background areas. As mentioned above, most SO2 4 exist in neutralized form as þ (NH4)2SO4. The correlation coefficient between SO2 4 and NH4 was above 0.8 for all cases, and the size distribution shapes were very þ similar, as shown in Fig. 4. The contributions of SO2 4 and NH4 appear to be about 80% for fine particles below 1.8 mm, measured by the MOUDI cascade impactor. The above result tells us that much and NHþ of the SO2 4 4 are secondary aerosols originating from anthropogenic sources. 2 However, the NHþ 4 /(SO4 þ NO3 ) equivalent ratios of PM2.5 and PM10 for sectors 1 and 2 at both sites were below 1.0, and differed 2 from the NHþ 4 /SO4 equivalent ratio. It appears that a portion of in the fine particles might have reacted with NHþ NO 3 4 to form NH4NO3. At both sites, the correlation coefficient between NO 3 and NHþ 4 was very high for PM2.5, contrary to PM10. So, fine-size NO3 existed in the form of NH4NO3 from HNO3 reacting with NH3. The lower concentration and contribution of NO 3 also appeared in summer and fall, because the NH4NO3 in fine particles volatilizes well under high temperature and dry environments. In general, fine-size NO 3 is formed along with HNO3 which is converted from reactions between NO2 originating from anthropogenic sources and OH radicals or VOCs. It appears that fine-size NO 3 undergoes longrange transport, since there are only few local NOx and VOCs sources at both sampling sites.
5563
NO 3 existed not only in fine particles but also in coarse ones. The size distribution of NO 3 showed a bimodal distribution with a higher peak in coarse (>1.8 mm) mode for Deokjeok and a smooth single mode for Gosan. The contribution of NO 3 was 66.0% and 36.9% in coarse (>1.8 mm) particles for Deokjeok and Gosan, respectively. Under a rich sea salt environment, HNO3 generates stable NaNO3 by reacting with NaCl in coarse mode (Wall et al., 1988), and HNO3 also reacts with other sea salt components such as MgCl2 and CaCl2. HNO3 generates coarse-size NO 3 through the reaction with crustal particles (Pakkanen, 1996). As a result of correlation analysis between NO 3 and other ionic components for coarse (>1.8 mm) mode, relatively higher correlation coefficients were seen for Mg2þ and Ca2þ, whereas the coefficients were very þ low for SO2 4 and NH4 . Therefore, coarse-size NO3 appears to be mostly present as reacted particles with sea salt or crustal particles. Carbon components exhibited different behaviors with respect to sector compared with secondary aerosol. As in the case of secondary aerosol, the relative contributions of OC and EC showed high values of 1.30 and 1.29 for Gosan sector 2, contrary to sector 1. For Deokjeok, however, the OC and EC contributions were similar for sectors 1 and 2. The relative carbon mass contributions were higher for Deokjeok and lower for Gosan. Overall OC/EC ratios of 4.0 and 3.6 were calculated for Deokjeok and Gosan, respectively. We believe the major factor is carbon emissions from northwest Korea. For OC, the emissions per unit area from northwest Korea is significantly larger, mostly originating
Fig. 5. The Asian emissions inventory dataset for carbon (unit: metric tons year1 0.5 cell1) (Reference: This Asia inventory dataset is developed in support of NASA’s INTEX-B mission (2006)).
5564
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
from residential sources. The OC/EC emission ratios were in the range of 1.1–1.8 for east China, north China, and south Korea, whereas that of northwest Korea showed a value of 4.5, based on the Asian emissions inventory dataset developed in support of INTEX-B, as illustrated in Fig. 5. The overall contribution of residential emissions was 96.4% for carbon emissions in northwest Korea and the OC/EC ratio was 4.9. In spring and summer, with a higher frequency for sector 2, the OC/EC ratios for Deokjeok were 3.8 and 3.4, respectively. However, a relatively higher ratio of 4.5 was seen in winter with a contribution of 68% for sector 1. For Gosan, the OC/EC ratio for sector 1 in winter was 4.2 with a relative contribution of 44%, and this ratio was the highest for any season. On the other hand, the ratio was 2.5 with a contribution of 15% in summer. Thereby, we concluded that Deokjeok was influenced more by northwest carbon emissions rather than in the case of Gosan. With minimal local sources, an OC/EC ratio of about 2.0 signifies that the OC is formed mostly from photochemical reaction.
However, the higher ratio of about 4.0, shown in our results above indicates that the effect of emissions dominated for both sites. Deokjeok and Gosan showed different behavior for Ca2þ and Mg2þ values originating from crustal or sea salt. The relative contribution of Ca2þ and Mg2þ for Deokjeok was about 1.3% for sectors 2 and 3. For Gosan, the highest contribution of Ca2þ appeared at sector 2, and sector 1 for Mg2þ. The major sources of Kþ are known to be crustal aerosol and biomass burning. For all cases, the highest contribution of Kþ appeared for sector 2 which was above 1.5. For Deokjeok sector 2 data, the high correlation coefficients between Kþ and the five major compounds of secondary þ aerosols (SO2 4 , NO3 , NH4 ) and carbon components (OC, EC) were 0.60–0.89. We believe that the main source of Kþ was biomass burning for PM2.5 and PM10. However, the Kþ behavior of PM2.5 and PM10 for sector 1 showed different properties even though its contributions were similar. A higher correlation coefficient of about 0.6 between Kþ and
Fig. 6. The aerosol images by SEM for Deokjeok.
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
secondary aerosol was seen for PM2.5, and the coefficients were also higher in the cases of Ca2þ(0.56) and Mg2þ(0.70), whereas, for PM10, the lower correlation coefficients between Kþ and secondary aerosol were in the range of 0.17–0.41, and the coefficients were similar with the pattern of crustal aerosol. For Deokjeok, hence, we confirmed that the major sources for Kþ were crustal aerosol and biomass burning for fine mode, but mostly crustal aerosol for coarse mode in sector 1. On the other hand, the two major sources for Kþ in PM2.5 were crustal aerosol and biomass burning for sectors 1 and 2 for Gosan. The correlations þ 2þ of Kþ with SO2 4 and NH4 were also higher, but not with NO3 , Ca , and Mg2þ. So we found that biomass burning was one of the major sources for Deokjeok but were not convinced whether biomass burning was the major source for sectors 1 and 2 for Gosan. From the results of sector 2 for Gosan during July 17–18 in 2007, the size distribution of Kþ showed a bimodal distribution with a peak at about 1 mm and relatively lower values in the range of 3– 4 mm. For sector 2, this tendency corresponded to the above conclusion that two major sources of Kþ were crustal aerosol and biomass burning for Gosan. The highest contribution of Naþ and Cl for Deokjeok was shown for sector 2, whereas the lowest contribution appeared for sector 1. Sector 1 trajectories for Deokjeok usually do not pass through any major water bodies and these air masses cannot be supplied with fresh sea salt. For sector 3, the contribution was lower for PM10 for Deokjeok because of the influence of precipitation. For Gosan, the highest contributions appeared for sector 4 and then for sector 3. Air masses of sector 4 for Gosan were supplied with fresh sea salt due to their trajectories passing over the ocean whereas the same sector passed through the Korean Peninsula for Deokjeok. Both sites had different contributions of Naþ and Cl for sector 3 because of varying wind speeds. The average wind speed was 3.6 m s1 for Deokjeok and was 8.9 m s1 for Gosan. The generation of fresh sea salt and its incorporation into these air masses is proportional to wind speed. As the results of single particle analysis for Deokjeok showed in Fig. 6 and Table 5, we could observe only reacted sea salt and no fresh sea salt for sector 1 on July 22–23 in 2007. For sector 5, chemical components showed different behaviors than that of mass contribution for both sites. It seemed that the relatively higher contribution was caused by aerosol from anthropogenic sources for Gosan. Higher contributions in the range of 1.26–1.92 for secondary aerosol and OC appeared, and the values Table 5 Relative contribution by single particle analysis. Stage (Particle size)
Stage 2 (2.5–10 mm)
Date
Jul. 20, 2007 Jul. 22–23, 2007 Jul. 20, 2007 Jul. 22–23, 2007
Category
Sector 3
Organic 42.4% OþSþC 2.0% AlSi 2.0% AlSi þ (N,S) 1.0% SiO2 2.0% CaCO3 Fresh sea salt 31.3% Reacted CaCO3 Reacted sea salt 7.1% 4.0% Reacted (CaCO3 þ sea salt) FeOx 1.0% Fly ash Reacted K species 3.0% (NH4)2SO4 Others 4.0% Total 100.0%
Stage 3 (1–2.5 mm)
Sector 1
Sector 3
Sector 1
6.3% 1.8% 16.6% 25.6% 0.4%
19.0% 28.0% 3.0% 2.0%
4.7% 32.7% 5.2% 14.2%
5.0% 9.0% 3.0% 17.0% 4.0%
14.7% 13.7% 0.9%
20.2% 10.8% 5.8% 1.8% 5.8% 0.4% 4.0% 0.4% 100.0%
0.0% 4.0%
6.0% 100.0%
0.9% 6.6% 4.7% 1.4% 100.0%
5565
were higher than that for sectors 1–4. The contribution of EC was also high, and with a value of 1.15%, whereas, lower contributions of crustal and sea salt were observed. 3.4. Aerosol characteristics by single particle analysis Some sample observations using single particle analysis for an episode at Deokjeok is as follows. For sector 1, most of the aerosols were reacted aerosols. The sum of reacted CaCO3, sea salt, CaCO3þsea salt, and K species were 37.2% and 34.0% for stage 2(2.5– 10 mm) and stage 3(1–2.5 mm), respectively. Here, the contribution was calculated by the number of aerosol particles, and a high contribution of AlSi was seen. The sum of AlSi and AlSiþ(N,S), generally originating from crustal aerosol, was 42.2% for stage 2 and 19.4% for stage 3. For sector 3, we observed a high concentration of organics and fresh sea salt on July 20 in 2007. Organics, fresh sea salt, and reacted sea salt had contributions of 42.4%, 31.3%, and 7.1% for stage 3, respectively. However, stages 2 and 3 had different characteristics for organics. Organics and fresh sea salt showed relatively lower contributions of 19.0% and 9.0%, respectively, but the contributions of 17.0% for reacted sea salt was relatively higher. For all cases, C, O, S complex aerosol showed a higher contribution in fine mode for stage 3, contrary to a lower contribution in coarse mode for stage 2. The higher contribution was about 30% in fine mode compared to that of about 2% in coarse mode. From the above results and the dark aerosol images and spherical shapes shown in Fig. 6, we could deduce that the C, O, S complex aerosol had been reacted. 4. Summary and conclusion We were able to deduce that large amounts of aerosol were influenced by continental long-range transport and that it was mostly caused by anthropogenic sources such as biomass burning, crustal aerosol, and chemical combinations of secondary aerosols. Air masses originating from the eastern and northern regions of China also heavily influenced both background sites. The frequency of trajectories for sector 1 originating from the north was higher than that of sector 2 originating from the west for both sites. The sum of air masses from sectors 1 and 2 commanded an absolute majority. Meanwhile, both sites had the lowest frequencies for sector 3 from the south and sector 4 from the east. From the results of relative contribution analysis, we could verify that influences from the continent far outweigh those from local sources for these two sites. The relative contributions were the highest for sector 2, while the lowest for sectors 3 and 4 originated from the oceans for both sites. For all cases, the mass concentration from sector 2 had the highest contribution, above 120%, compared with the overall average. However, the relative contributions for sectors 1 and 2 showed different characteristics between Deokjeok and Gosan. It seemed that the different pattern for sector 1 was caused by the differing relative distances between the measuring sites and north China which includes the northeast industrial complexes. It is also thought that the differences in meteorological properties such as temperature and relative humidity for sector 1 between Deokjeok and Gosan occurred due to changing air mass properties during transport. The highest contribution for most ionic and carbon components of PM2.5 and PM10 for both sites also appeared for sector 2. In particular, a relatively high contribution of above 1.4 was observed in the secondary aerosol case. The sum of relative contribution for þ secondary aerosols such as SO2 4 , NH4 , and NO3 in PM2.5 and PM10 was about 40% for sector 2, and this shows that there was a large influence of long-range transported pollutants from China. We can
5566
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
state that the SO2 concentration was mainly influenced by 4 photochemical reactions at relatively high temperature and large SO2 emissions from east China. It is also quite evident that NHþ 4 is mostly influenced by continental sources than those from local NH3 2 sources based on the NHþ 4 /SO4 equivalent ratio that is above 1:1 and the location of both sites being in relatively clean background areas. Most SO2 4 existed in its neutralized form, (NH4)2SO4, and it seemed that fine-size NO 3 was transported by long-range transport in the form of NH4NO3 and coarse-size NO 3 was mostly present as reacted particles, sea salt or crustal. Carbon components exhibited different behaviors for sectors 1 and 2, relative to secondary aerosols. The OC and EC contributions for Deokjeok were similar for sectors 1 and 2. However, the contribution of carbon components for Gosan showed high values for only sector 2. It was observed that the relative carbon mass contributions were higher for Deokjeok and lower for Gosan. We also confirmed that the major sources for Kþ were crustal aerosol and biomass burning partly based on a bimodal size distribution and the relationship between Kþ and other components. We found most of the aerosol to have been reacted for sector 1, and a high percentage of organics and fresh sea salt for sector 3. For all cases, C, O, S complex aerosols showed higher contributions in fine mode, contrary to a lower contribution in coarse mode. Acknowledgments This research was supported in part by the 2005–07 ‘‘Research for Chemical Characteristics and Behavior of Long-range Transport Aerosol’’ project sponsored by the Korea National Institute of Environmental Research (NIER) and we thank them for their support. References Alfaro, S.C., et al., 2003. Chemical and optical characterization of aerosols measured in spring 2002 at the ACE-Asia supersite, Zhenbeitai, China. Journal of Geophysical Research 108, 8641. Begum, B.A., Kim, E., Jeong, C.H., Lee, D.W., Hopke, P.K., 2005. Evaluation of the potential source contribution function using the 2002 Quebec forest fire episode. Atmospheric Environment 39, 3719–3724. Covert, D.S., Gras, J.L., Wiedensohler, A., Stratmann, F., 1998. Comparison of directly measured CCN with CCN modeled from the number-size distribution in the marine boundary layer during ACE 1 at Cape Grim, Tasmania. Journal of Geophysical Research 103, 16597–16608. Davis, B.L., Jixiang, G., 2000. Airborne particulate study in five cities of China. Atmospheric Environment 34, 2703–2711. Draxler, R.R., 1996. Boundary layer isentropic and kinematic trajectories during the august 1993 North Atlantic regional experiment Intensive. Journal of Geophysical Research 101, 29255–29268. Draxler, R.R., Hees, G.D., 1997. Description of the HYsplit_4 modeling System. NOAA Technical Memorandum ERL ARL-224. Draxler, R.R., Hees, G.D., 1998. An overview of the HYsplit_4 modeling system for trajectories, dispersion, and deposition. Australian Meteorological Magazine 47, 295–308. Fan, A.X., Hopke, P.K., Raunemaa, T.M., Oblad, M., Pacyna, J.M., 1995. A study on the potential sources of air pollutants – observed at Tjorn, Sweden. Environmental Science and Pollution Research 2, 107–115. Gao, N., Cheng, M.D., Hopke, P.K., 1993. Potential source contribution function analysis and source apportionment of sulfur species measured at Rubidoux, CA during the southern California air quality study, 1987. Analytica et Chimica Acta 277, 369–380.
Hafner, W.D., Hites, R.A., 2003. Potential sources pesticides, PCBs, and PAHs to the atmosphere of the Great Lakes. Environmental Science and Technology 37, 3764–3773. He, Z., Kim, Y.J., Ogunjobi, K.O., Hong, C.S., 2003. Characteristics of PM2.5 species and long-range transport of air masses at Taean background station, South Korea. Atmospheric Environment 37, 219–230. Hsu, Y.K., Holsen, T.M., Hopke, P.K., 2003. Locating and quantifying PCB sources in Chicago: receptor modeling and field sampling. Environmental Science and Technology 37, 681–690. Hwang, H., Ro, C.U., 2005. Single-particle characterization of four aerosol samples collected in ChunCheon, Korea, during Asian dust storm events in 2002. Journal of Geophysical Research – Atmospheres 110 Art.no. D23201. Hwang, H., Ro, C.U., 2006. Direct observation of nitrate and sulfate formations from mineral dust and sea-salts using low-Z particle EPMA. Atmospheric Environment 40, 3869–3880. Kim, H.S., Huh, J.B., Hopke, P.K., Holsen, T.M., Yi, S.M., 2007. Characteristics of the major chemical constituents of PM2.5 and smog events in Seoul, Korea in 2003 and 2004. Atmospheric Environment 41, 6762–6770. Lee, J.H., Kim, Y.P., Moon, K.C., Kim, H.K., Lee, C.B., 2001. Fine particle measurements at two background sites in Korea between 1996 and 1997. Atmospheric Environment 35, 635–643. Lee, S.B., Bae, G.N., Kim, Y.P., Jin, H.C., Yoon, Y.S., Moon, K.C., 2002. Aerosol characteristics at Tokchok island in the Yellow sea. Atmospheric Environment 18, 305–316. Lee, Y.S., Cha, J.W., Kim, Y.K., Lee, H.W., Park, J.K., Jeon, B.I., Cho, C.B., Chung, H.S., 2006. Seasonal aerosol optical properties at Anmyon-do global atmosphere Watch Observatory, Korea. Journal of the Korean Meteorological Society 42 (5), 265–275. Lee, H.l., Park, S.S., Kim, K.W., Kim, Y.J., 2008. Source identification of PM2.5 particles measured in Gwangju, Korea. Atmospheric Research 88, 199–211. NASA, 2006. The Asian emissions inventory from the INTEX-B project. Available at: http://www-air.larc.nasa.gov/missions/intex-b/intexb.html. NOAA/ARL, 2007. NOAA ARL HYSPLIT (HYbrid single-particle Lagrangian integrated trajectory) model. Available at: http://gcmd.nasa.gov/records/NOAA-HYSPLIT. html. Pakkanen, T.A., 1996. Study of formation of coarse particle nitrate aerosol. Atmospheric Environment 30, 2475–2482. Perry, K.D., Cahill, T.A., Schnell, R.C., Harris, J.M., 1999. Long-range transport of anthropogenic aerosols to the National Oceanic and Atmospheric Administration baseline station at Mauna Loa Observatory, Hawaii. Journal of Geophysical Research 104 (D15), 18521–18533. Poissant, L., Pilote, M., 1998. Mercury concentrations in single event precipitation in southern. Quebec. The Science of The Total Environment. 213, 65–72. Polissar, A.V., Hopke, P.K., Malm, W.C., Sisler, J.F., 1998. Atmospheric aerosol over Alaska. 2. Elemental composition and sources. Journal of Geophysical Research 103, 19045–19057. Putaud, J.P., et al., 2004. A European aerosol phenomenology 2: chemical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe. Atmospheric Environment 38, 2579–2595. Quinn, P.K., Bates, T.S., Johnson, J.E., Covert, D.S., Charlson, R.J., 1990. Interactions between the sulfur and reduced nitrogen cycles over the central Pacific Ocean. Journal of Geophysical Research 95, 16405–16416. Richter, A., Burrows, J.P., Nu¨ß, H., Granier, C., Niemeier, U., 2005. Increase in tropospheric nitrogen dioxide over China observed from space. Nature 437, 129–132. Ro, C.U., Hwang, H., Kim, H.K., Chun, Y.S., Van Grieken, R., 2005. Single-Particle characterization of four ‘‘Asian dust’’ samples collected in Korea, using Low-Z particle electron probe X-ray microanalysis. Environmental Science and Technology 39, 1409–1419. Song, C.H., Carmichael, G.R., 1999. The aging process of naturally emitted aerosol (sea-salt and mineral aerosol) during long range transport. Atmospheric Environment 33, 2203–2218. Streets, D.G., Tsai, N.Y., Akimoto, H., Oka, K., 2001. Trends in emissions of acidifying species in Asia, 1985–1997. Water, Air, and Soil Pollution 130, 187–192. Wall, S.M., John, W., Ondo, J.L., 1988. Measurement of aerosol size distributions for nitrate and major ionic species. Atmospheric Environment 22, 1649–1656. Woo, J.H., Baek, J.M., Kim, J.W., Carmichael, G.R., Thongboonchoo, N., Kim, S.T., An, J.H., 2003. Development of a multi-resolution emission inventory and its impact on sulfur distribution for northeast asia. Water, Air, and Soil Pollution 148, 259–278.
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Chemical characteristics of long-range transport aerosol at background sites in Korea Yoo Jung Kim a, Jung-Hun Woo b, Young-Il Ma a, Suhyang Kim b, Jung Sik Nam a, Hakyoung Sung b, Ki-Chul Choi b, Jihyun Seo a, Jeong Su Kim c, Chang-Hee Kang d, Gangwoong Lee e, Chul-Un Ro f, Duk Chang a, Young Sunwoo b, * a
Department of Environmental Engineering, Konkuk University, Seoul, Republic of Korea Department of Advanced Technology Fusion, Konkuk University, Seoul, Republic of Korea Global Environment Research Center, National Institute of Environmental Research, Incheon, Republic of Korea d Department of Chemistry, Cheju National University, Jeju, Republic of Korea e Department of Environmental Science, Hankuk University of Foreign Studies, Youngin, Republic of Korea f Department of Chemistry, Inha University, Incheon, Republic of Korea b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 July 2008 Received in revised form 28 March 2009 Accepted 31 March 2009
In this study, background concentration sites of Deokjeok and Gosan, which were deemed suitable for monitoring the impact of long-range transported air pollutants, were selected. An investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at both sites using appropriate methodologies to make initial estimations was conducted. Episodic measurements of PM2.5, PM10, and size distribution, along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. As for frequency of wind direction, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. For PM2.5 and PM10, the mass concentrations from north and east China were higher than other cases, originating from the ocean. In the northerly-wind case, meteorological properties for Deokjeok and Gosan and the influence of carbon emissions from northwest Korea resulted in a changing of air mass properties during transport. As was the case with mass concentration, the highest contribution for ionic and carbon components of PM2.5 and PM10 for both sites appeared for the westerly wind case. A specially high relative contribution, greater than 1.4 times, was apparent in the secondary aerosol case because of a large influence of long-range transported pollutants from east China. Carbon components exhibited different behaviors for the northerly and westerly wind cases compared with secondary aerosol. The major reason for this discrepancy appears to be the carbon emissions from northwest Korea. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
Keywords: Aerosol Background concentration Long-range transport East Asia
1. Introduction The long-range transport of air pollutants in Northeast Asia is a very relevant current issue. Northeast Asia suffers from mass emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from China (Streets et al., 2001). In recent years, the annual growth rate of nitrogen dioxide (NO2) concentration over the industrial areas in China has significantly increased, as high as about 50% during 1996–2004(Richter et al., 2005). The Korean Peninsula is located on the eastern edge of the continent of Asia and lies in a belt of prevailing westerlies
* Corresponding author. Tel.: þ82 2 450 3541; fax: þ82 2 453 2706. E-mail address: [email protected] (Y. Sunwoo).
accompanying seasonally changing centers of atmospheric presng peninsula sure. The distance between Seoul in Korea and Sh ando in China is approximately 400 km. Therefore, the impacts of longrange transport of pollutant emissions from the industrial centers of eastern China and uplifted dust particles from the relatively dry regions further inland are quite severe (Lee et al., 2001; Davis and Jixiang, 2000). Therefore, much research has been performed and reported for the background atmospheric monitoring of long-range transport air pollutants in Korea. However, multiple background monitoring sites are needed for the analysis of the impact of rapidly increasing long-range transported air pollutants such as SO2, NOx, and particles, and a large volume of data should be collected for construction of a reliable database for the major pollutants. Thus, we have selected suitable background concentration sites for monitoring
1352-2310/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.03.062
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
the impact of long-range transported air pollutants, and conducted an investigation of the source types of pollutants, their locations, and relative quantitative contributions to the particulate concentrations at the sites using appropriate methodologies to make initial estimations. 2. Monitoring and analysis methodology 2.1. Study location and monitoring data After a long-term survey for finding the proper background concentration sites suitable for monitoring the impact of longrange transport of air pollutants, the monitoring sites of Deokjeok and Gosan were selected in this study. Both sites are located along the western coast of Korea, close to the eastern coast of China. Deokjeok (37130 N, 126 90 E) is located to the west of the Korean Peninsula, and Gosan (33170 N, 126100 E) is situated on the west coast of Jeju Island off the southern tip of the Korean Peninsula as illustrated in Fig. 1. Both sites are located on islands and there are no large anthropogenic sources adjacent to the sites. The island of Deokjeok covers 20.9 km2 and there are no industrial facilities, little transportation and a population of one thousand. Forests and fields cover almost 90% of the area. Passenger ships shuttle only 3–4 times everyday and there is little other traffic. Emissions per unit area and population density for Ongjin county which contain many islands including Deokjeok, were low relative to near by neighboring counties. Aerosol concentration levels for Deokjeok were also relatively lower than those for national background monitoring sites, Gangwha and Taean, on the west coastal region (Lee ndo ng peninsula, including one et al., 2002). On a regional scale, Sha of the biggest industrial complexes in China, is located merely 330 km to the west of Deokjeok. Incheon city, in Korea, is located 70 km to the east. Deokjeok was the farthest island from the Korean
5557
Peninsula in the ‘‘West Sea’’, where electric power was available to run experimental equipments. The Gosan site is considered an ideal location to monitor background atmospheric concentrations in the northeast Asia region. The Korean mainland and Shanghai, in China, are located over 100 km and 500 km away, respectively. There are no large local industrial sources. This site is located on the west edge of Jeju island. Gosan was a super site during the ACE-Asia project (Alfaro et al., 2003) and many experiments were performed at this location. So, Deokjeok and Gosan satisfy most of the conditions for monitoring background air quality. Episodic measurements of PM2.5, PM10, and size distribution along with its ion and carbon components were performed from 2005 to 2007, and a comprehensive analysis of the results was conducted utilizing back trajectory analysis. The sampling was carried out over a total of 91 days divided into 8 periods as follows: October 15–24 in 2005, January 5–19, April 1–15, June 6–15, October 15–25 in 2006 and January 11–20, April 16–25, July 16–25 in 2007. Teflon filter packs connected to cyclones (URG, 16.7 L min1) with cut-off diameters of 2.5 mm and 10 mm were used for measurement of PM2.5 and PM10. We used a MOUDI (Micro-Orifice Uniform Deposit Impactors; MSP, Model 100 with rotator-8 stage or without rotator-10 stage) for size distribution with 30 L min1 flow late. The MOUDI is comprised of 8 stages with cut-off diameters of 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, and 0.18 mm, respectively. Additional cut-off points at 0.1 and 0.056 mm are provided with the 10 stage model. The Teflon filters (Gelman Sciences, pore size 2.0 mm, 47 m ø) and quartz filters (Whatman, 47 mm ø) were exchanged at 9 am everyday. Size distribution sampling was carried out every 2–4 days for two samples per sampling period. Mass and ionic concentrations were measured using teflon filters. Carbon components were captured utilizing baked quartz filters. Mass concentration was measured using gravimetric analysis for PM2.5, PM10, and size
Fig. 1. Location of background monitoring sites.
5558
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
þ þ 2þ 2þ distribution. Ionic components, such as NHþ 4 , Na , K , Ca , Mg , , NO and Cl , of particles were analysed by the Ion ChromaSO2 4 3 tography method (Dionex, ICS-2000). Carbon components including elemental carbon and organic carbon of PM2.5 were analysed using the TOT (Thermal Optical Transmittance) method.
2.2. Back trajectory analysis Lagrangian trajectories were used to identify the pathways of the air mass transport for estimation of source–receptor relationships of the air pollutants. The trajectories reflect the large-scale atmospheric transport characteristics of air masses to the sampling sites. The trajectories were estimated using the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model with integrated data for hemispheric upper air. Back trajectory analysis provides a better understanding of air flow and long-range transport patterns. We analysed the aerosol characteristics with respect to categorized back trajectories for initial estimation of source location and quantitative contribution. 72-h back trajectories were calculated using the HYSPLIT model from NOAA (NOAA/ARL, 2007; Draxler, 1996; Draxler and Hees, 1997, 1998) with an endpoint height of 500 m. Input data for HYSPLIT utilized the framework of FNL (Final Run) meteorological
data which are 6-hourly archived data from GDAS (Global Data Assimilation System) of NCEP (National Centers for Environmental Prediction). In this study, the modeling was performed for GMT from 0 to 24 to correspond with the local time of 9 am for filter change at the sampling site. Polissar et al. (1998) suggested the endpoint height of 500 m for looking at patterns in the wind field of air masses at 100–600 m height to define the source locations and long-rage transport patterns in Barrow, Alaska. The value of this height to represent average PBL (Planetary Boundary Level) was widely used by many researchers (Fan et al., 1995; Gao et al., 1993; Hafner and Hites, 2003; Hsu et al., 2003; Begum et al., 2005; Poissant and Pilote, 1998; Polissar et al., 1998). 72 h were adequate for most trajectories, passing through major source regions like Fig. 2. Hwang and Ro (2005), Lee et al. (2006, 2008) used 72-h back trajectories to identify air mass pathways. We categorized the trajectories into 5 sectors according to the air mass pathways as follows. The air masses originating from the Chinese or Russian continent without passing any major water body (thus having to come from the north direction for the above monitoring sites) were categorized as sector 1. Those coming from the Chinese continent and passing the ‘‘West Sea’’ and entering the peninsula through the west coast of Korea were denoted as sector 2. Those originating from the oceans without having passed through
Fig. 2. Examples of 72-h back trajectories for the four sectors.
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
China were categorized as sector 3. These air masses mostly came from the south. Those originating from China or Russia and entering the peninsula through the east coast of Korea were designated as sector 4. Finally, the air masses moving much slower than that of other sectors or spinning around the measurement sites were categorized as sector 5. The trajectories in sector 5 lay near the sampling sites for an extended period of time. Representative examples of the 5 sectors, as mentioned above, are shown in Fig. 2. 2.3. Single particle analysis Single particle analysis was also performed to evaluate the types and the quantitative characteristics of individual aerosols for the summer, 2007 data. A single particle analysis technique, low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA), was applied to characterize the aerosol samples collected at Deokjeok for 3 days on July 20, 22, and 23 in 2007. We sampled twice, at 10 am and 6 pm. Particles were collected on aluminum foil using a three-stage cascade impactor sampler (Dekati, PM10 Impactor). This impactor, with a sampling flow rate of 10 L min1, has aerodynamic cut-off diameters of 10, 2.5, and 1 mm in stages #1–3, respectively. Particles larger than the size of 10 mm are collected at the first stage of the impactor, while the size of collected particles are in the range of 10–2.5 mm in stage 2 and 2.5–1 mm in stage 3, respectively. The quantitative determination of concentrations of low-Z elements such as C, N, and O in individual particles was carried out by low-Z particle EPMA using an X-ray detector equipped with an ultra-thin window (Hwang and Ro, 2006; Ro et al., 2005). 2.4. Emissions in Northeast Asia We analysed the results of an Asian emissions inventory from the INTEX-B project (NASA, 2006) to understand more precisely the aerosol characteristics and their sources. This emission inventory was prepared by Qiang Zhang and David G. Streets, Decision and Information Sciences Division, Argonne National Laboratory, for the INTEX-B project of the National Aeronautics and Space Administration (NASA). This inventory includes the emissions of SO2, NOx, CO, VOC, PM10, PM2.5, BC, and OC by sector (power, industry, residential, and transportation) and six speciated VOCs by sector files. This data set is only for anthropogenic emissions in 2006 and the resolution of this inventory is 0.5 degrees. The INTEX-B is one of many experiments that aim to understand the transport and transformation of gases and aerosols on transcontinental/intercontinental scales and assess their impacts on air quality and climate. The INTEX-B was carried out in the spring of 2006.
(Perry et al., 1999), and compared to natural background data of Europe, by about 3–5 mg m3 for PM2.5 and 5–8 mg m3 for PM10 (Putaud et al., 2004). The correlation between the two sites was not high, because each site has differing local meteorological properties and different episodic periods because a distance of approximately 400 km separates the two sites even though they almost have the same longitude. High PM2.5 to PM10 ratios of 78.6% for Deokjeok and 77.3% for Gosan, were prevalent, and the ratio for Deokjeok was similar to that of Gosan. The major ionic components in PM2.5 and PM10 were SO2 4 , NO3 , for both sites (Table 1). Carbon is also a major component and NHþ 4 in PM2.5 and OC has a higher concentration than EC. For all cases, þ SO2 4 showed the highest concentration, with OC, NH4 , NO3 and EC in decreasing order. The concentrations of other ionic components have relatively large differences. High contributions of secondary pollutants (33.5–43.7%) and carbon (18.9–19.9%) aerosol showed the influence of anthropogenic sources. Carbon aerosol in PM10 and some other major components, including metals and elemental S in PM2.5, were not analysed. This is likely a major reason for the relatively high unknown contribution. 3.2. Sector frequency and meteorological property Table 2 shows the relative frequency and local meteorological properties from AWS (Auto Weather System) data of categorized air masses. The travel path was categorized according to sectors at Deokjeok and Gosan as mentioned previously. We performed back trajectory analyses except for the 13 non-categorized cases (14.3%) for Deokjeok and 16 days (17.6%) for Gosan where the trajectories moved through more than two sectors in one day. A frequency of 33.0% for sector 1, originating from the north, was the highest for Deokjeok, and that of sector 2, originating from the west, was 27.5%. For Gosan, frequencies of 22.0% and 31.9% were obtained for sectors 1 and 2, respectively. The sum of air masses from sectors 1 and 2 made up 60.5% and 53.9% for Deokjeok and Gosan, respectively. Meanwhile, both sites had lower frequencies for sector 3 from the south and sector 4 from the east. In case of
Table 1 Aerosol concentration and contribution. PM10
PM2.5 Mean
SD
Contribution
Mean
SD
Contribution
32.8 6.0 2.4 2.6 0.3 0.1 0.4 0.4 0.2
33.8 5.9 2.4 1.9 0.3 0.1 0.3 0.4 0.2
100.0% 18.2% 7.3% 8.0% 1.0% 0.3% 1.1% 1.1% 0.7%
12.0 4.7 1.4 1.6 0.2 0.04 0.2 0.3 0.3
100.0% 26.8% 6.5% 10.4% 1.1% 0.3% 1.2% 1.9% 1.2%
Deokjeok
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl OC EC Unknown
25.7 5.4 1.7 2.3 0.2 0.1 0.3 0.2 0.2 3.8 1.0 10.5
23.0 5.6 2.0 1.8 0.2 0.05 0.3 0.2 0.2 2.1 0.5
100.0% 20.9% 6.7% 9.0% 0.8% 0.2% 1.1% 0.8% 0.6% 15.0% 3.9% 41.0%
Gosan
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl OC EC Unknown
17.6 4.8 1.0 1.9 0.2 0.04 0.2 0.3 0.2 2.7 0.8 5.6
11.2 4.4 1.0 1.5 0.1 0.03 0.2 0.2 0.2 1.7 0.5
100.0% 27.0% 5.7% 10.8% 0.9% 0.2% 1.2% 1.6% 1.1% 15.5% 4.4% 31.7%
3. Results and discussion 3.1. Overall aerosol characteristics The averages and standard deviations of PM2.5 and PM10 mass concentrations for Deokjeok were higher than that of Gosan. PM2.5 mass concentrations for Deokjeok and Gosan during the overall sampling period were 25.3 22.6 and 17.2 10.8 mg m3, respectively. PM10 mass concentrations for Deokjeok and Gosan were 32.2 32.7 mg m3 and 22.3 11.6 mg m3, respectively. The daily variations of both sites were quite similar. This aerosol concentration level represents typical regional characteristics in Northeast Asia. This level is relatively higher than global background data, by about 1 mg m3 for PM2.5 than at Mauna Loa, Hawaii
5559
20.5 22.3 6.0 1.4 2.3 0.2 0.1 0.3 0.4 0.3
11.3
57.4%
50.6%
5560
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
Table 2 Sector frequency and meteorology properties.
Deokjeok
Frequency Temperature Relative Humidity Wind Speed Precipitation day Precipitation contribution Precipitation Averagea
Gosan
Frequency Temperature Relative Humidity Wind Speed Precipitation day Precipitation contribution Precipitation Averagea
a
Sector 1
Sector 2
Sector 3
Sector 4
Sector 5
30 days 33.0% 4.4 C 58.6% 3.4 m s1 4 days 13.3% 0.7 mm day1
25 days 27.5% 13.4 C 70.2% 4.0 m s1 3 days 12.0% 1.1 mm day1
8 days 8.8% 19.0 C 89.7% 3.6 m s1 5 days 62.5% 12.6 mm day1
10 days 11.0% 11.9 C 61.7% 3.3 m s1 1 day 10.0% 0.8 mm day1
5 days 5.5% 14.1 C 76.6% 5.9 m s1 2 days 40.0% 3.9 mm day1
20 days 22.0% 11.4 C 67.7% 7.7 m s1 4 days 20.0% 1.3 mm day1
29 days 31.9% 14.7 C 68.0% 6.8 m s1 6 days 20.7% 0.9 mm day1
13 days 14.3% 18.8 C 85.9% 8.9 m s1 9 days 69.2% 12.2 mm day1
8 days 8.8% 15.6 C 64.5% 4.9 m s1 1 day 12.5% 0.01 mm day1
5 days 5.5% 13.7 C 76.7% 4.8 m s1 1 day 20% 1.4 mm day1
Precipitation average ¼ overall precipitation for each sector/frequency day for each sector.
sector 5, where the air masses are moving slower than that of other sectors or spinning around the sites, impact was minimal relative to other sectors due to a relatively low concentration of 5.5% at both sites. Thus, it was quite apparent that the two sites are heavily influenced by air masses originating from the eastern and northern regions of China. This result reflects the general wind pattern in the Korean Peninsula. Kim et al. (2007) identified the transport pattern of about 35% originating from Central-Southern China and Northern China-Mongolia from March 2003 to February 2005. He et al. (2003) performed cluster analysis with back trajectories from March 1998 to July 1999, and reported that a group of trajectories ndo ng peninsula and ‘‘West Sea’’ made through Northern China, Sha up 70% and another group, about 28%, through Russia, Mongolia and Northeastern China. Meteorological characteristics appear significant for some cases. In particular, sector 1 for Deokjeok characteristically had cold and relatively dry air masses. An average temperature of 4.4 C and a relative humidity of 58.6% for Deokjeok showed lower temperatures compared with other sectors in the range of 11.9–19.0 C. However, air masses of sector 1 for Gosan had a quite different behavior. Although the relative humidity (67.7%) was similar with other sectors, the temperature (11.4 C) was only slightly lower than that of other sectors. The differences of temperature and relative humidity between Deokjeok and Gosan for sector 1 were 7.0 C and 9.1%, respectively. It should be noted that air masses having pathways from the north were most likely heated and supplied with vapor while passing across the section between Deokjeok and Gosan. Thus, we looked closely at back trajectories for sector 1 on similar days in winter to find detailed reasons for the difference, and 9 days were selected. The differences of temperature and relative humidity between Deokjeok and Gosan at the conditions as referred to above were quite similar. An average temperature of 1.6 C and a relative humidity of 53.6% were obtained for Deokjeok while the temperature and relative humidity for Gosan were 6.2 C and 65.0%, respectively. The vertical profile for sector 1 showed that the altitude of air masses dropped near Deokjeok and went on to Gosan maintaining low altitude. For sector 3, air masses with precipitation appeared frequently and the relative humidity was about 70% for both sites. Average precipitation signifies overall precipitation divided by total days for each sector. It was 12.6 mm day1 and 12.2 mm day1 for Deokjeok and Gosan, respectively, and is quite unique compared to other sectors. The highest relatively humidity of about 90% and a temperature of 19 C compared with other sectors were seen in
this sector. For sector 3, all days, except just one day in summer for Deokjeok, were selected as experimental days, while similar contributions were seen in spring and summer for Gosan. It is believed that hot and damp air masses were heavily influenced by tropical cyclones. For sector 5, different behaviors were seen for Deokjeok and Gosan. The two sites did not overlap for the same days in sector 5. Back trajectories of Deokjeok showed air masses moving slower than that of other sectors or spinning around the sites. By applying back trajectories extending back 120 hours, however, it could be seen that the sector 5 air masses of Gosan moved slowly through the Korean Peninsula and originated from east China.
3.3. Aerosol characteristics The individual average concentration level for each sector was considered by the contribution ratio of each sector average versus the overall average.
Relative contribution ¼
sector average conc: overall average conc:
Overall average, as mentioned above, does not mean 91 days but actual experimental days of 78 and 75 days for Deokjeok and Gosan, respectively, excluding non-categorized cases. We also classified the sectors into 1–4 and 5 for the detailed analysis of aerosol characteristics in this study, because sectors 1–4 represented long-range transported air masses. Table 3 shows relative contributions of mass and chemical components of each sector for both sites, especially PM2.5 and PM10. For all cases, the mass concentration from sector 2 had the highest contribution 120%, compared to the overall average. The relative contributions for sectors 1 and 2 from north and east China were also higher, while sectors 3 and 4, originating from the oceans showed lower contributions. However, the relative contributions for sectors 1 and 2 showed different characteristics between Deokjeok and Gosan. The relative contribution for sector 1 for Gosan was below 1, whereas that of PM2.5 (1.38) and PM10 (1.33) dominated sector 2. For Deokjeok, the relative contribution for sector 2 was slightly lower than Gosan, and a higher value of about 1.1 appeared for sector 1. It seems that different patterns for sector 1 are caused by the differing relative distances between the two measuring sites and north China which includes the northeast industrial complexes. It also seems that the difference between meteorological properties such as
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
5561
Table 3 Sector relative contribution of mass and chemical components. Deokjeok
Gosan
Sector 1
Sector 2
Sector 3
Sector 4
Sector5
Sector1
Sector2
Sector3
Sector4
Sector5
PM2.5
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl OC EC
1.05 0.74 0.72 0.79 0.86 0.91 0.74 0.67 0.84 1.14 1.10
1.31 1.55 1.71 1.44 1.37 1.27 1.61 1.40 1.22 1.10 1.18
0.67 1.18 0.39 1.02 1.24 1.33 0.86 1.28 1.50 0.76 0.58
0.50 0.33 0.58 0.48 0.50 0.60 0.47 0.99 0.85 0.72 0.76
0.72 0.92 0.86 1.11 0.64 0.34 0.60 0.64 0.58 0.58 0.65
0.85 0.69 0.93 0.70 1.00 1.14 0.80 0.83 1.03 0.98 0.96
1.38 1.47 1.41 1.43 1.23 1.03 1.52 0.89 0.76 1.30 1.29
0.42 0.52 0.25 0.57 0.67 0.78 0.45 1.20 1.06 0.38 0.55
0.60 0.29 0.58 0.35 0.57 1.06 0.20 1.41 1.86 0.72 0.65
1.56 1.92 1.52 1.87 1.26 0.72 1.39 1.17 0.75 1.30 1.15
PM10
Mass SO2 4 NO 3 NHþ 4 2þ Ca Mg2þ Kþ Naþ Cl
1.11 0.77 0.87 0.84 0.92 0.85 0.83 0.87 0.73
1.22 1.53 1.47 1.40 1.21 1.29 1.49 1.25 1.28
0.66 1.06 0.30 0.94 1.33 1.24 0.68 0.77 1.28
0.53 0.33 0.66 0.48 0.60 0.70 0.62 1.06 1.00
0.71 1.01 1.26 1.12 0.76 0.73 0.64 0.74 0.81
0.86 0.74 0.91 0.76 1.27 1.10 0.86 0.82 1.07
1.33 1.43 1.42 1.39 1.06 1.01 1.51 0.98 0.73
0.48 0.49 0.27 0.51 0.64 0.85 0.36 1.11 1.16
0.65 0.40 0.58 0.49 0.53 0.92 0.27 1.29 1.58
1.56 1.82 1.51 1.83 1.24 1.09 1.27 1.12 0.92
temperature and relative humidity for sector 1 between Deokjeok and Gosan occurs due to changing air mass properties during transport. The contributions were the highest for sector 2 and lowest for sectors 3 and 4 for both sites. This indicates that influences by the continent far outweigh those from local urban sources for these two sites. Sector 5 for Deokjeok showed a relatively lower contribution of about 0.7, but the contribution for Gosan was very high, over 1.5. In some episodic cases, air masses for sector 5 for Gosan moved slowly through Korea and east China. It seemed that the major cause of these episodic cases was the effect of air pollutants accumulating in slow-moving air masses. However, we could not clearly identify the major source location, east China or South Korea. More case studies for sector 5 will be needed to verify this. As with mass concentration, the highest contribution for almost all ionic and carbon components of PM2.5 and PM10 for both sites appeared for sector 2. In particular, a high relative contribution of above 1.4 was seen in the secondary aerosol case. In any case, the
relative contribution of secondary aerosol for sector 2 is higher than that of mass contribution. It seems that a primary reason is large emission of SO2, NOx, and NH3 from industrial complexes in the east coast of China. Relatively large emission sources of NH3, SO2 and NOx are located in the east coast of China, as illustrated in Fig. 3, based on the Asian emissions inventory dataset developed in support of the INTEX-B project (NASA, 2006) and other preceeding results on emissions (Woo et al., 2003). It takes approximately 2–4 days for gaseous precursors to þ transform in the atmosphere to particulate SO2 4 , NH4 , and NO3 . Air mass trajectories from the west appeared frequently, as mentioned previously, and it took about 3 days for the transport of air masses from east China to both sites. Therefore, it is reasonable to think that much of the secondary aerosol originated from east China. The sum of relative contribution for secondary aerosol such as SO2 4 , NHþ 4 , and NO3 in PM2.5 and PM10 is about 40% for sector 2. So, it appears that there is a large influence of long-range transported pollutants from China.
Fig. 3. The Asian emissions inventory dataset for SO2 and NOx (unit: metric tons year1 0.5 cell1) (Reference: This Asia inventory dataset is developed in support of NASA’s INTEX-B mission (2006)).
5562
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
Table 4 Sector equivalent ratio. Sector 1
Sector 2
Sector 3
Sector 4
Sector 5
PM2.5
PM10
PM2.5
PM10
PM2.5
PM10
PM2.5
PM10
PM2.5
PM10
Deokjeok
2 NHþ 4 /(SO4 ) 2 /(SO NHþ 4 4 þ NO3 )
1.24 0.99
1.28 0.95
0.97 0.75
1.07 0.83
0.99 0.92
1.02 0.93
1.71 1.17
1.68 1.05
1.38 1.12
1.28 0.93
Gosan
2 NHþ 4 /(SO4 ) 2 NHþ 4 /(SO4 þ NO3 )
1.10 0.90
1.08 0.87
1.06 0.91
1.02 0.87
1.17 1.08
1.13 1.00
1.31 0.98
1.01 0.85
1.05 0.93
1.06 0.91
The concentration and relative contribution of SO2 4 had the highest value for every sector at both sites. The concentration and increased in proportion to temperature, contribution of SO2 4 especially for sector 2 and the summer season. The winter/summer concentration ratio of SO2 4 for PM2.5 was 25.0% and for PM10 32.8% at Deokjeok, and 53.3% for PM2.5 and 63.9% for PM10 at Gosan. The temperature differences between summer and winter were 22.3 C for Deokjeok and 10.8 C for Gosan. Thus, we could surmise that the concentration was largely influenced by photochemical SO2 4 reaction at high temperature and large SO2 emissions in east China. Concentrations of NHþ 4 appear to be influenced by emissions from anthropogenic sources rather than biogenic sources. In the
2 clear ocean region, NHþ 4 does not neutralize SO4 due to lower NH3 þ concentrations (Covert et al., 1998). The NH4 /SO2 4 equivalent ratio was suggested to be about 0.65 in the clean Pacific ocean (Quinn et al., 1990). When the condition for neutralization is sufficient, that 2 is, when the reacted NHþ 4 to SO4 ratio is above 1:1, then this is good evidence of local NH3 sources. Then the NHþ 4 is converted from NH3 during long-range transport (Song and Carmichael, 2 1999). The NHþ 4 /SO4 equivalent ratios of PM2.5 and PM10 were both above 1.1 for both sites regardless of the sectors for the overall experimental period (Table 4). The ratios are above 1.0 for every sector except PM2.5 for sectors 2 and 3 at Deokjeok. Although these ratios were below 1.0, they were 0.97 and 0.99 for each sector,
Fig. 4. Secondary aerosol size distribution.
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
respectively. We tentatively concluded that the continental influence by far outweigh those from local NH3 sources for NHþ 4 , because both sites are located in relatively clean background areas. As mentioned above, most SO2 4 exist in neutralized form as þ (NH4)2SO4. The correlation coefficient between SO2 4 and NH4 was above 0.8 for all cases, and the size distribution shapes were very þ similar, as shown in Fig. 4. The contributions of SO2 4 and NH4 appear to be about 80% for fine particles below 1.8 mm, measured by the MOUDI cascade impactor. The above result tells us that much and NHþ of the SO2 4 4 are secondary aerosols originating from anthropogenic sources. 2 However, the NHþ 4 /(SO4 þ NO3 ) equivalent ratios of PM2.5 and PM10 for sectors 1 and 2 at both sites were below 1.0, and differed 2 from the NHþ 4 /SO4 equivalent ratio. It appears that a portion of in the fine particles might have reacted with NHþ NO 3 4 to form NH4NO3. At both sites, the correlation coefficient between NO 3 and NHþ 4 was very high for PM2.5, contrary to PM10. So, fine-size NO3 existed in the form of NH4NO3 from HNO3 reacting with NH3. The lower concentration and contribution of NO 3 also appeared in summer and fall, because the NH4NO3 in fine particles volatilizes well under high temperature and dry environments. In general, fine-size NO 3 is formed along with HNO3 which is converted from reactions between NO2 originating from anthropogenic sources and OH radicals or VOCs. It appears that fine-size NO 3 undergoes longrange transport, since there are only few local NOx and VOCs sources at both sampling sites.
5563
NO 3 existed not only in fine particles but also in coarse ones. The size distribution of NO 3 showed a bimodal distribution with a higher peak in coarse (>1.8 mm) mode for Deokjeok and a smooth single mode for Gosan. The contribution of NO 3 was 66.0% and 36.9% in coarse (>1.8 mm) particles for Deokjeok and Gosan, respectively. Under a rich sea salt environment, HNO3 generates stable NaNO3 by reacting with NaCl in coarse mode (Wall et al., 1988), and HNO3 also reacts with other sea salt components such as MgCl2 and CaCl2. HNO3 generates coarse-size NO 3 through the reaction with crustal particles (Pakkanen, 1996). As a result of correlation analysis between NO 3 and other ionic components for coarse (>1.8 mm) mode, relatively higher correlation coefficients were seen for Mg2þ and Ca2þ, whereas the coefficients were very þ low for SO2 4 and NH4 . Therefore, coarse-size NO3 appears to be mostly present as reacted particles with sea salt or crustal particles. Carbon components exhibited different behaviors with respect to sector compared with secondary aerosol. As in the case of secondary aerosol, the relative contributions of OC and EC showed high values of 1.30 and 1.29 for Gosan sector 2, contrary to sector 1. For Deokjeok, however, the OC and EC contributions were similar for sectors 1 and 2. The relative carbon mass contributions were higher for Deokjeok and lower for Gosan. Overall OC/EC ratios of 4.0 and 3.6 were calculated for Deokjeok and Gosan, respectively. We believe the major factor is carbon emissions from northwest Korea. For OC, the emissions per unit area from northwest Korea is significantly larger, mostly originating
Fig. 5. The Asian emissions inventory dataset for carbon (unit: metric tons year1 0.5 cell1) (Reference: This Asia inventory dataset is developed in support of NASA’s INTEX-B mission (2006)).
5564
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
from residential sources. The OC/EC emission ratios were in the range of 1.1–1.8 for east China, north China, and south Korea, whereas that of northwest Korea showed a value of 4.5, based on the Asian emissions inventory dataset developed in support of INTEX-B, as illustrated in Fig. 5. The overall contribution of residential emissions was 96.4% for carbon emissions in northwest Korea and the OC/EC ratio was 4.9. In spring and summer, with a higher frequency for sector 2, the OC/EC ratios for Deokjeok were 3.8 and 3.4, respectively. However, a relatively higher ratio of 4.5 was seen in winter with a contribution of 68% for sector 1. For Gosan, the OC/EC ratio for sector 1 in winter was 4.2 with a relative contribution of 44%, and this ratio was the highest for any season. On the other hand, the ratio was 2.5 with a contribution of 15% in summer. Thereby, we concluded that Deokjeok was influenced more by northwest carbon emissions rather than in the case of Gosan. With minimal local sources, an OC/EC ratio of about 2.0 signifies that the OC is formed mostly from photochemical reaction.
However, the higher ratio of about 4.0, shown in our results above indicates that the effect of emissions dominated for both sites. Deokjeok and Gosan showed different behavior for Ca2þ and Mg2þ values originating from crustal or sea salt. The relative contribution of Ca2þ and Mg2þ for Deokjeok was about 1.3% for sectors 2 and 3. For Gosan, the highest contribution of Ca2þ appeared at sector 2, and sector 1 for Mg2þ. The major sources of Kþ are known to be crustal aerosol and biomass burning. For all cases, the highest contribution of Kþ appeared for sector 2 which was above 1.5. For Deokjeok sector 2 data, the high correlation coefficients between Kþ and the five major compounds of secondary þ aerosols (SO2 4 , NO3 , NH4 ) and carbon components (OC, EC) were 0.60–0.89. We believe that the main source of Kþ was biomass burning for PM2.5 and PM10. However, the Kþ behavior of PM2.5 and PM10 for sector 1 showed different properties even though its contributions were similar. A higher correlation coefficient of about 0.6 between Kþ and
Fig. 6. The aerosol images by SEM for Deokjeok.
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
secondary aerosol was seen for PM2.5, and the coefficients were also higher in the cases of Ca2þ(0.56) and Mg2þ(0.70), whereas, for PM10, the lower correlation coefficients between Kþ and secondary aerosol were in the range of 0.17–0.41, and the coefficients were similar with the pattern of crustal aerosol. For Deokjeok, hence, we confirmed that the major sources for Kþ were crustal aerosol and biomass burning for fine mode, but mostly crustal aerosol for coarse mode in sector 1. On the other hand, the two major sources for Kþ in PM2.5 were crustal aerosol and biomass burning for sectors 1 and 2 for Gosan. The correlations þ 2þ of Kþ with SO2 4 and NH4 were also higher, but not with NO3 , Ca , and Mg2þ. So we found that biomass burning was one of the major sources for Deokjeok but were not convinced whether biomass burning was the major source for sectors 1 and 2 for Gosan. From the results of sector 2 for Gosan during July 17–18 in 2007, the size distribution of Kþ showed a bimodal distribution with a peak at about 1 mm and relatively lower values in the range of 3– 4 mm. For sector 2, this tendency corresponded to the above conclusion that two major sources of Kþ were crustal aerosol and biomass burning for Gosan. The highest contribution of Naþ and Cl for Deokjeok was shown for sector 2, whereas the lowest contribution appeared for sector 1. Sector 1 trajectories for Deokjeok usually do not pass through any major water bodies and these air masses cannot be supplied with fresh sea salt. For sector 3, the contribution was lower for PM10 for Deokjeok because of the influence of precipitation. For Gosan, the highest contributions appeared for sector 4 and then for sector 3. Air masses of sector 4 for Gosan were supplied with fresh sea salt due to their trajectories passing over the ocean whereas the same sector passed through the Korean Peninsula for Deokjeok. Both sites had different contributions of Naþ and Cl for sector 3 because of varying wind speeds. The average wind speed was 3.6 m s1 for Deokjeok and was 8.9 m s1 for Gosan. The generation of fresh sea salt and its incorporation into these air masses is proportional to wind speed. As the results of single particle analysis for Deokjeok showed in Fig. 6 and Table 5, we could observe only reacted sea salt and no fresh sea salt for sector 1 on July 22–23 in 2007. For sector 5, chemical components showed different behaviors than that of mass contribution for both sites. It seemed that the relatively higher contribution was caused by aerosol from anthropogenic sources for Gosan. Higher contributions in the range of 1.26–1.92 for secondary aerosol and OC appeared, and the values Table 5 Relative contribution by single particle analysis. Stage (Particle size)
Stage 2 (2.5–10 mm)
Date
Jul. 20, 2007 Jul. 22–23, 2007 Jul. 20, 2007 Jul. 22–23, 2007
Category
Sector 3
Organic 42.4% OþSþC 2.0% AlSi 2.0% AlSi þ (N,S) 1.0% SiO2 2.0% CaCO3 Fresh sea salt 31.3% Reacted CaCO3 Reacted sea salt 7.1% 4.0% Reacted (CaCO3 þ sea salt) FeOx 1.0% Fly ash Reacted K species 3.0% (NH4)2SO4 Others 4.0% Total 100.0%
Stage 3 (1–2.5 mm)
Sector 1
Sector 3
Sector 1
6.3% 1.8% 16.6% 25.6% 0.4%
19.0% 28.0% 3.0% 2.0%
4.7% 32.7% 5.2% 14.2%
5.0% 9.0% 3.0% 17.0% 4.0%
14.7% 13.7% 0.9%
20.2% 10.8% 5.8% 1.8% 5.8% 0.4% 4.0% 0.4% 100.0%
0.0% 4.0%
6.0% 100.0%
0.9% 6.6% 4.7% 1.4% 100.0%
5565
were higher than that for sectors 1–4. The contribution of EC was also high, and with a value of 1.15%, whereas, lower contributions of crustal and sea salt were observed. 3.4. Aerosol characteristics by single particle analysis Some sample observations using single particle analysis for an episode at Deokjeok is as follows. For sector 1, most of the aerosols were reacted aerosols. The sum of reacted CaCO3, sea salt, CaCO3þsea salt, and K species were 37.2% and 34.0% for stage 2(2.5– 10 mm) and stage 3(1–2.5 mm), respectively. Here, the contribution was calculated by the number of aerosol particles, and a high contribution of AlSi was seen. The sum of AlSi and AlSiþ(N,S), generally originating from crustal aerosol, was 42.2% for stage 2 and 19.4% for stage 3. For sector 3, we observed a high concentration of organics and fresh sea salt on July 20 in 2007. Organics, fresh sea salt, and reacted sea salt had contributions of 42.4%, 31.3%, and 7.1% for stage 3, respectively. However, stages 2 and 3 had different characteristics for organics. Organics and fresh sea salt showed relatively lower contributions of 19.0% and 9.0%, respectively, but the contributions of 17.0% for reacted sea salt was relatively higher. For all cases, C, O, S complex aerosol showed a higher contribution in fine mode for stage 3, contrary to a lower contribution in coarse mode for stage 2. The higher contribution was about 30% in fine mode compared to that of about 2% in coarse mode. From the above results and the dark aerosol images and spherical shapes shown in Fig. 6, we could deduce that the C, O, S complex aerosol had been reacted. 4. Summary and conclusion We were able to deduce that large amounts of aerosol were influenced by continental long-range transport and that it was mostly caused by anthropogenic sources such as biomass burning, crustal aerosol, and chemical combinations of secondary aerosols. Air masses originating from the eastern and northern regions of China also heavily influenced both background sites. The frequency of trajectories for sector 1 originating from the north was higher than that of sector 2 originating from the west for both sites. The sum of air masses from sectors 1 and 2 commanded an absolute majority. Meanwhile, both sites had the lowest frequencies for sector 3 from the south and sector 4 from the east. From the results of relative contribution analysis, we could verify that influences from the continent far outweigh those from local sources for these two sites. The relative contributions were the highest for sector 2, while the lowest for sectors 3 and 4 originated from the oceans for both sites. For all cases, the mass concentration from sector 2 had the highest contribution, above 120%, compared with the overall average. However, the relative contributions for sectors 1 and 2 showed different characteristics between Deokjeok and Gosan. It seemed that the different pattern for sector 1 was caused by the differing relative distances between the measuring sites and north China which includes the northeast industrial complexes. It is also thought that the differences in meteorological properties such as temperature and relative humidity for sector 1 between Deokjeok and Gosan occurred due to changing air mass properties during transport. The highest contribution for most ionic and carbon components of PM2.5 and PM10 for both sites also appeared for sector 2. In particular, a relatively high contribution of above 1.4 was observed in the secondary aerosol case. The sum of relative contribution for þ secondary aerosols such as SO2 4 , NH4 , and NO3 in PM2.5 and PM10 was about 40% for sector 2, and this shows that there was a large influence of long-range transported pollutants from China. We can
5566
Y.J. Kim et al. / Atmospheric Environment 43 (2009) 5556–5566
state that the SO2 concentration was mainly influenced by 4 photochemical reactions at relatively high temperature and large SO2 emissions from east China. It is also quite evident that NHþ 4 is mostly influenced by continental sources than those from local NH3 2 sources based on the NHþ 4 /SO4 equivalent ratio that is above 1:1 and the location of both sites being in relatively clean background areas. Most SO2 4 existed in its neutralized form, (NH4)2SO4, and it seemed that fine-size NO 3 was transported by long-range transport in the form of NH4NO3 and coarse-size NO 3 was mostly present as reacted particles, sea salt or crustal. Carbon components exhibited different behaviors for sectors 1 and 2, relative to secondary aerosols. The OC and EC contributions for Deokjeok were similar for sectors 1 and 2. However, the contribution of carbon components for Gosan showed high values for only sector 2. It was observed that the relative carbon mass contributions were higher for Deokjeok and lower for Gosan. We also confirmed that the major sources for Kþ were crustal aerosol and biomass burning partly based on a bimodal size distribution and the relationship between Kþ and other components. We found most of the aerosol to have been reacted for sector 1, and a high percentage of organics and fresh sea salt for sector 3. For all cases, C, O, S complex aerosols showed higher contributions in fine mode, contrary to a lower contribution in coarse mode. Acknowledgments This research was supported in part by the 2005–07 ‘‘Research for Chemical Characteristics and Behavior of Long-range Transport Aerosol’’ project sponsored by the Korea National Institute of Environmental Research (NIER) and we thank them for their support. References Alfaro, S.C., et al., 2003. Chemical and optical characterization of aerosols measured in spring 2002 at the ACE-Asia supersite, Zhenbeitai, China. Journal of Geophysical Research 108, 8641. Begum, B.A., Kim, E., Jeong, C.H., Lee, D.W., Hopke, P.K., 2005. Evaluation of the potential source contribution function using the 2002 Quebec forest fire episode. Atmospheric Environment 39, 3719–3724. Covert, D.S., Gras, J.L., Wiedensohler, A., Stratmann, F., 1998. Comparison of directly measured CCN with CCN modeled from the number-size distribution in the marine boundary layer during ACE 1 at Cape Grim, Tasmania. Journal of Geophysical Research 103, 16597–16608. Davis, B.L., Jixiang, G., 2000. Airborne particulate study in five cities of China. Atmospheric Environment 34, 2703–2711. Draxler, R.R., 1996. Boundary layer isentropic and kinematic trajectories during the august 1993 North Atlantic regional experiment Intensive. Journal of Geophysical Research 101, 29255–29268. Draxler, R.R., Hees, G.D., 1997. Description of the HYsplit_4 modeling System. NOAA Technical Memorandum ERL ARL-224. Draxler, R.R., Hees, G.D., 1998. An overview of the HYsplit_4 modeling system for trajectories, dispersion, and deposition. Australian Meteorological Magazine 47, 295–308. Fan, A.X., Hopke, P.K., Raunemaa, T.M., Oblad, M., Pacyna, J.M., 1995. A study on the potential sources of air pollutants – observed at Tjorn, Sweden. Environmental Science and Pollution Research 2, 107–115. Gao, N., Cheng, M.D., Hopke, P.K., 1993. Potential source contribution function analysis and source apportionment of sulfur species measured at Rubidoux, CA during the southern California air quality study, 1987. Analytica et Chimica Acta 277, 369–380.
Hafner, W.D., Hites, R.A., 2003. Potential sources pesticides, PCBs, and PAHs to the atmosphere of the Great Lakes. Environmental Science and Technology 37, 3764–3773. He, Z., Kim, Y.J., Ogunjobi, K.O., Hong, C.S., 2003. Characteristics of PM2.5 species and long-range transport of air masses at Taean background station, South Korea. Atmospheric Environment 37, 219–230. Hsu, Y.K., Holsen, T.M., Hopke, P.K., 2003. Locating and quantifying PCB sources in Chicago: receptor modeling and field sampling. Environmental Science and Technology 37, 681–690. Hwang, H., Ro, C.U., 2005. Single-particle characterization of four aerosol samples collected in ChunCheon, Korea, during Asian dust storm events in 2002. Journal of Geophysical Research – Atmospheres 110 Art.no. D23201. Hwang, H., Ro, C.U., 2006. Direct observation of nitrate and sulfate formations from mineral dust and sea-salts using low-Z particle EPMA. Atmospheric Environment 40, 3869–3880. Kim, H.S., Huh, J.B., Hopke, P.K., Holsen, T.M., Yi, S.M., 2007. Characteristics of the major chemical constituents of PM2.5 and smog events in Seoul, Korea in 2003 and 2004. Atmospheric Environment 41, 6762–6770. Lee, J.H., Kim, Y.P., Moon, K.C., Kim, H.K., Lee, C.B., 2001. Fine particle measurements at two background sites in Korea between 1996 and 1997. Atmospheric Environment 35, 635–643. Lee, S.B., Bae, G.N., Kim, Y.P., Jin, H.C., Yoon, Y.S., Moon, K.C., 2002. Aerosol characteristics at Tokchok island in the Yellow sea. Atmospheric Environment 18, 305–316. Lee, Y.S., Cha, J.W., Kim, Y.K., Lee, H.W., Park, J.K., Jeon, B.I., Cho, C.B., Chung, H.S., 2006. Seasonal aerosol optical properties at Anmyon-do global atmosphere Watch Observatory, Korea. Journal of the Korean Meteorological Society 42 (5), 265–275. Lee, H.l., Park, S.S., Kim, K.W., Kim, Y.J., 2008. Source identification of PM2.5 particles measured in Gwangju, Korea. Atmospheric Research 88, 199–211. NASA, 2006. The Asian emissions inventory from the INTEX-B project. Available at: http://www-air.larc.nasa.gov/missions/intex-b/intexb.html. NOAA/ARL, 2007. NOAA ARL HYSPLIT (HYbrid single-particle Lagrangian integrated trajectory) model. Available at: http://gcmd.nasa.gov/records/NOAA-HYSPLIT. html. Pakkanen, T.A., 1996. Study of formation of coarse particle nitrate aerosol. Atmospheric Environment 30, 2475–2482. Perry, K.D., Cahill, T.A., Schnell, R.C., Harris, J.M., 1999. Long-range transport of anthropogenic aerosols to the National Oceanic and Atmospheric Administration baseline station at Mauna Loa Observatory, Hawaii. Journal of Geophysical Research 104 (D15), 18521–18533. Poissant, L., Pilote, M., 1998. Mercury concentrations in single event precipitation in southern. Quebec. The Science of The Total Environment. 213, 65–72. Polissar, A.V., Hopke, P.K., Malm, W.C., Sisler, J.F., 1998. Atmospheric aerosol over Alaska. 2. Elemental composition and sources. Journal of Geophysical Research 103, 19045–19057. Putaud, J.P., et al., 2004. A European aerosol phenomenology 2: chemical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe. Atmospheric Environment 38, 2579–2595. Quinn, P.K., Bates, T.S., Johnson, J.E., Covert, D.S., Charlson, R.J., 1990. Interactions between the sulfur and reduced nitrogen cycles over the central Pacific Ocean. Journal of Geophysical Research 95, 16405–16416. Richter, A., Burrows, J.P., Nu¨ß, H., Granier, C., Niemeier, U., 2005. Increase in tropospheric nitrogen dioxide over China observed from space. Nature 437, 129–132. Ro, C.U., Hwang, H., Kim, H.K., Chun, Y.S., Van Grieken, R., 2005. Single-Particle characterization of four ‘‘Asian dust’’ samples collected in Korea, using Low-Z particle electron probe X-ray microanalysis. Environmental Science and Technology 39, 1409–1419. Song, C.H., Carmichael, G.R., 1999. The aging process of naturally emitted aerosol (sea-salt and mineral aerosol) during long range transport. Atmospheric Environment 33, 2203–2218. Streets, D.G., Tsai, N.Y., Akimoto, H., Oka, K., 2001. Trends in emissions of acidifying species in Asia, 1985–1997. Water, Air, and Soil Pollution 130, 187–192. Wall, S.M., John, W., Ondo, J.L., 1988. Measurement of aerosol size distributions for nitrate and major ionic species. Atmospheric Environment 22, 1649–1656. Woo, J.H., Baek, J.M., Kim, J.W., Carmichael, G.R., Thongboonchoo, N., Kim, S.T., An, J.H., 2003. Development of a multi-resolution emission inventory and its impact on sulfur distribution for northeast asia. Water, Air, and Soil Pollution 148, 259–278.