Young Sung Ghim

Source apportionment of fine carbonaceous particles by positive matrix factorization at Gosan background site in East Asia

Fine particle (aerodynamic diameter <2.5 microm) samples were collected during six intensive measurement periods from November 2001 to August 2003 at Gosan, Jeju Island, Korea, which is one of the representative background sites in East Asia. Chemical composition of these aerosol samples including major ion components, trace elements, organic and elemental carbon (OC and EC), and particulate polycyclic aromatic hydrocarbons (PAHs) were analyzed to study the impact of long-range transport of anthropogenic aerosol. Aerosol chemical composition data were then analyzed using the positive matrix factorization (PMF) technique in order to identify the possible sources and estimate their contribution to particulate matter mass. Fourteen sources were then resolved including soil dust, fresh sea salt, transformed natural source, ammonium sulfate, ammonium nitrate, secondary organic carbon, diesel vehicle, gasoline vehicle, fuel oil combustion, biomass burning, coal combustion, municipal incineration, metallurgical emission source, and volcanic emission. The PMF analysis results of source contributions showed that the natural sources including soil dust, fresh and aged sea salt, and volcanic emission contributed to about 20% of the measured PM(2.5) mass. Other primary anthropogenic sources such as diesel and gasoline vehicle, coal and fuel oil combustion, biomass burning, municipal incineration, metallurgical source contributed about 34% of PM(2.5) mass. Especially, the secondary aerosol mainly involved with sulfate, nitrate, ammonium, and organic carbon contributed to about 39% of the PM(2.5) mass.

Characteristics of ground-level ozone distributions in Korea for the period of 1990–1995

General characteristics and trends of ground-level ozone were investigated by using observations from over 80 stations in Korea for the period of 1990–1995. In general, seasonal ozone variations are characterized by a spring peak with decreased levels in the summer, followed by increases in the fall. In summer, owing to frequent precipitation, monthly average ozone levels notably decreased in most coastal areas, while a weak depression was observed in inland stations, sustained by photochemical ozone buildup under relatively low wind speeds. Coupled with frequent precipitation in summer, with high ozone-forming potential, low wind speeds in inland areas play a significant role in local variations of ozone concentrations. Accordingly, ozone concentrations vary in a quite different manner among monitoring stations in the Greater Seoul Area, as well as among major cities nationwide. On the whole, monthly average ozone concentrations in major cities, whether located in inland or coastal areas, are about 10–20 ppb lower than background levels of 30–40 ppb typical of the Northern Hemisphere. These lower concentrations are likely due to the titration effect of local NOx emissions, which is a clear indication of urban characteristics for most of the stations. Next, ozone concentration variations at 34–37 stations in the Greater Seoul Area, characterized by typical photochemical air pollution, were closely investigated. Special efforts were made to clarify the effects of transport within the Greater Seoul Area on the ozone concentration variations, a long-standing question at issue, by examining monthly variations of percentile values and frequency distributions of hourly ozone concentrations. It is believed that complex local variations across the nation are superimposed on underlying effects from the Asian continent and the ocean, located to the west and northeast of the Korean Peninsula, respectively. Further research is needed to quantify the relative importance of these effects in controlling the nationwide distribution of ozone levels.

Visibility trends in Korea during the past two decades.

Abstract Temporal trends and spatial distributions of visibility measured by the human eye over 60 stations in Korea between 1980 and 2000 are analyzed and discussed. Generally, visibility is lowest on winter mornings and highest on summer afternoons throughout Korea. Visibility in Seoul is now in an increasing trend while it has decreased nationwide, especially in clean coastal areas. Spatial distribution of visibility in the 1990s was related negatively to that of relative humidity (RH). However, visibility generally decreased despite an overall decrease in RH throughout the country. Air pollutants should have played a role in this dissonant variation, particularly in relatively clean areas and on summer afternoons. It was interpreted that the visibility increase in major metropolitan areas, including the greater Seoul area, in the 1990s was caused mainly by the reduction in pollutant emissions by rigorous government policy. But the effect of the emission reduction was manifested with decreasing RH.

Meteorological Effects on the Evolution of High Ozone Episodes in the Greater Seoul Area

ABSTRACT Three high O3 episodes—7 days in 1992 (July 3–July 9), 9 days in 1994 (July 21–July 29), and another 3 days in 1994 (August 22–August 24)—were selected on the basis of morning (7:00 a.m.–10:00 a.m.) average wind direction and speed and daily maximum O3 concentrations in the greater Seoul, Korea, of 1990–1997. To better understand their characteristics and life cycles, surface data from the Seoul Weather Station (SWS) and surface and 850-hPa wind field data covering northeast Asia around the Korean Peninsula were used for the analysis. In the July 1992 episode, westerly winds were most frequent as a result of the influence of a high-pressure system west of the Korean Peninsula behind a trough. In contrast, in the July 1994 episode, easterly winds were most frequent as a result of the effect of a typhoon moving north from the south of Japan. Despite different prevailing wind directions, the peak O3 concentrations for each episode occurred when a sea/land breeze developed in association with weak synoptic forcing. The August 1994 episode, which was selected as being representative of calm conditions, was another typical example in which a well-developed sea/land breeze helped cause the peak O3 concentration to rise to a record high of 322 parts per billion by volume (ppbv). All three high O3 episodes ended as a result of precipitation, and subsequent rises in O3 concentrations were also suppressed by a series of precipitation events afterwards. In particular, two heavy rainfalls were the main reason why the August 1994 episode, which had the highest and second-highest O3 concentrations, lasted only a few days.

Dry Deposition of Reactive Nitrogen and Sulfur Compounds in the Greater Seoul Area

While deposition is a removal process of pollutants from the atmosphere, it is an intake process of such pollutants into the ground. It is suggested that surface waters in the Greater Seoul Area, used as a source of drinking water, have been affected by severe air pollution. In this work, the dry deposition of reactive nitrogen and sulfur species was estimated for three typical days in each season for the year of 1997. The CIT (California Institute of Technology) photochemical model incorporated with a gaseous oxidation reaction of SO2 was used. The study revealed that reactive nitrogen deposition was the largest in summer and sulfur deposition was the largest in winter. Most of the reactive nitrogen was deposited in the form of HNO3 and NO2, but HNO3 deposition is highly dependent on the season according to the extent of photochemical production. On the other hand, the contribution of sulfate to the total deposition of sulfur was minimal partly because of low deposition velocity and of the neglect of possible inflow from the boundaries. Approximately 53% of the reactive nitrogen and 30% of the sulfur emitted in the study area was deposited in the ground in the dry form on an annual basis.

Determination of domain for diagnostic wind field estimation in Korea

Abstract A diagnostic routine is applied to estimate wind fields for two coastal areas with mountains in Korea. The reliability of the predicted wind fields is assessed by calculating the maximum differences of wind speed and direction between two successive estimations by increasing the size of the estimation domain over the target domain. The differences decrease and stabilize after a critical increment to produce an optimum domain size used to estimate wind fields. Although a larger radius of influence and a larger grid size could increase the stability of convergence, they smooth the predicted wind field and decrease the resolution. The study also reveals that the estimated wind field shows larger differences from the wind field obtained with all stations available in the country, at higher mountains along the boundaries beyond which stations would be added if larger domains are employed.

Long-term Trend Analysis of Korean Air Quality and Its Implication to Current Air Quality Policy on Ozone and PM10

Nation-wide systematic and comprehensive measurements of air quality criteria species have been made over 340 sites currently in Korea since 1990. Using these data, temporal and spatial trends of SO₂, PM10, NO₂, O3, CO and Ox(NO₂+O₃) were analyzed to characterize and evaluate implementing efficiency of air quality policy and regulations. Due to strict and effective policy to use cleaner fuels in late 1980s and 1990s, the primary pollutants, such as SO₂, CO, and PM10 decreased sharply by early 2000s in all parts of Korea. After this period, their concentrations declined with much lower rates in most parts of Korea. In addition, isolated but noticeable numbers of places, especially in major ports, newly developing towns and industrial parks, sustained high levels or even showed further degradation. Despite series of emission control strategies were enforced since early 1990s, NO₂ concentrations haven’t changed much till 2005, due to significant increase in number of automobiles. Nevertheless, we confirmed that the staggering levels of NO₂ and PM10 improved evidently after 2005, especially in Seoul Metropolitan Area (SMA), where enhanced regulations for NO₂ and PM10 emissions was imposed to automobiles and large emission sources. However, their decreasing trends were much lessened in recent years again as current air quality improvement strategies has been challenged to revise further. In contrast to these primary species, annual O₃, which is secondary product from NO₂ and volatile organic compounds (VOCs), has increased consistently with about 0.6 ppbv per year in every urban part of Korea, while yearly average of daily maximum 8-hour O₃ in summer season had a much higher rate of 1.2 ppbv per year. Increase of O₃ can be explained mainly by reductions of NO emission. Rising background O₃ in the Northeast Asia and increasing oxidizing capacity by changing photochemistry were likely causes of observed O₃ increase. The future air quality policy should consider more effective ways to lower alarming level of O₃ and PM10.

An Assessment Study for the Urban Air Monitoring Network in Seoul

Twenty-five stations of the urban monitoring network in Seoul were assessed with a focus on surveillance function of the exceedances of 8-hour ozone and 24-hour PM10 standards. The two standards were selected because their attainment rates were particularly low. Two hierarchical cluster analyses were performed to group stations with similar atmospheric environments-one using daily highest 8-hour [O3+NO2], 8-hour O3 concentrations plus corresponding 8-hour NO2 concentrations considering the interconversion of O3 and NO2, and the other using 24hour PM10 concentrations. An index to measure higher concentration and exceedances of the standards was introduced. Within a cluster, sufficiently high score was assigned to the trends station or the station with higher index. Scores for O3+NO2 and PM10 of a given station were added and ranked in the descending order to determine the relative importance.