• Progress in Superconductivity and Cryogenics
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• v.24 no.2
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• pp.23-26
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• 2022

A lossless transport of an arbitrary waveform in a frequency range of 10⁶-10⁹ Hz through a conduction channel in a cryogenic temperature is of importance for a high-speed operation of quantum device. However, it is hard to use a commercial oscilloscope to directly detect the waveform travelling in a device located in a cryogenic system. Here, we developed a cryogenic voltage sampling technique by using a Schottky barrier gate prepared on a surface of a GaAs/AlGaAs device, which revealed that an incident rectangle waveform can transport through a 1 mm long two-dimensional conduction channel without waveform deformation up to 20 MHz, while further study is needed to increase the detection frequency.

• Journal of Korean Society for Atmospheric Environment
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• v.25 no.2
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• pp.99-107
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• 2009

This paper reviews the current status of mercury research on exposure and contamination, mercury emissions, emission limits and control technologies, long-range transport and deposition research, and mercury management policy in Korea. According to a monitoring of the Ministry of Environment and the Ministry of Health and Welfare, blood mercury levels among Koreans are $5{\sim}8$ times higher than those of U.S. and Germany. The most dominant source of exposure to mercury is through dietary intake. Emissions of mercury from coal-fired power plants are estimated 8.93 ton/year in 2004. Emissions of mercury from other important sources, such as waste incineration, steel and cement manufacturing and non-ferrous metal smelting operations are to be further investigated. A study on long-range transport of mercury suggests that the dry deposition flux over the Yellow Sea was much greater than those for other oceans. As a whole, the amounts of wet depositions of nitrogen and sulfur were 1.9 and 1.5 times larger than the amounts of dry depositions in each species, respectively. Substantial influence from China caused by high emissions in East China and westerly wind was possibly suggested. However, the influence from nitrogen emission in Korea was also confirmed. Korean Government has already adopted stringent emission limits on mercury for incinerators and boilers in 2005. However, emission limits for coal-fired power plants and non-ferrous metal smelters are rather relaxed. As the above mentioned two sources can be two most important sources of mercury emissions, control strategy for those sources are to be considered.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.3
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• pp.418-429
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• 2018

Measurements of 24-hr size-segregated ambient particles were made at an urban site of Gwangju under high pressure conditions occurred in the Korean Peninsula late in March 2018. The aim of this study was to understand the effect of air stagnation on mass size distributions and formation pathways of water-soluble organic and inorganic components. During the study period, the $NO_3{^-}$, $SO_4{^{2-}}$, $NH_4{^+}$, water-soluble organic carbon (WSOC), and humic-like substances(HULIS) exhibited mostly bi-modal size distributions peaking at 1.0 and $6.2{\mu}m$, with predominant droplet modes. In particular, outstanding droplet mode size distributions were observed on March 25 when a severe haze occurred due to stable air conditions and long range transport of aerosol particles from northeastern regions of China. Air stagnation conditions and high relative humidity during the study period resulted in accumulation of primary aerosol particles from local emission sources and enhanced formation of secondary ionic and organic aerosols through aqueous-phase oxidations of $SO_2$, $NO_2$, $NH_3$, and volatile organic compounds, leading to their dominant droplet mode size distributions at particle size of $1.0{\mu}m$. From the size distribution of $K^+$ in accumulation mode, it can be inferred that in addition to the secondary organic aerosol formations, accumulation mode WSOC and HULIS could be partly attributed to biomass burning emissions.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.E1
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• pp.21-28
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• 2002

Air quality issues in Korea rapidly changed at the beginning of the 1990s from primary to secondary pollutants starting in Seoul, the capital of Korea. The present frame of national air pollution monitoring networks was established between the end of the 1980s and the beginning of the 1990s. Background monitoring was initiated in the middle of the 1990s in response to increasing public concern about the long-range transport of air pollutants. Apart from the national monitoring, both routine and intensive measurements of fine particles have been made for research purposes since the middle of the 1990s at several background sites. However, air pollution monitoring in urban areas for other purposes was relatively scarce as national monitoring has been concentrated in these areas. Although ozone pollution has become a significant issue in major metropolitan areas every summer, only a little information on ozone precursors is available. During the past few years, the number of national monitoring stations has greatly increased. The government has a plan to gradually expand monitoring items as well as stations. It is anticipated that highly detailed information on both photochemical reactants and products will be available within the next several years. More emphasis will be placed on toxic substances based on risk assessment in monitoring for both research and policy making.

• Journal of Environmental Impact Assessment
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• v.16 no.6
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• pp.533-542
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• 2007

The general characteristics of fine particle and meteorological analysis of high $PM_{10}$ concentration day which was over $100{\mu}g/m^3$ in busan were investigated for period of 2002 to 2006. Annual mean concentration including Asian dust day was $68.7{\mu}g/m^3$ in 2002, $54.6{\mu}g/m^3$ in 2003, $60.4{\mu}g/m^3$ in 2004, $58.3{\mu}g/m^3$ in 2005 and $58.8{\mu}g/m^3$ in 2006, respectively. Seasonal mean concentration was $73.4{\mu}g/m^3$ in Springtime, $56.8{\mu}g/m^3$ in Summertime, $55.5{\mu}g/m^3$ in Wintertime and $54.4{\mu}g/m^3$ in Falltime, respectively. Mean concentration for land use was 69.2 $37.0{\mu}g/m^3$ in industrial area, 64.2 $35.5{\mu}g/m^3$ in rural area, 62.6 $34.4{\mu}g/m^3$ in commercial area and 55.3 $33.8{\mu}g/m^3$ in residential area, respectively. Frequency of synoptic pattern for high $PM_{10}$ concentration day was 18 days(16.7%) in I type, 27 days(25.0%) in II type, 10 days(9.3%) in III type, 5 days(4.6%) in IV type, 13 days(12.0%) in V type and 29 days (26.9%) in VI type, respectively. Frequency of long range transport sector for high $PM_{10}$ concentration day was 9 days(8.3%) in I type, 64 days(59.5%) in II type, 34 days(31.5%) in III type, 1 days in IV type, 0 days, respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.6
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• pp.631-639
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• 2007

We examined diurnal and seasonal variations of ozone ($O_3$) concentrations and its relation to meteorological parameters observed at the Ieodo Ocean Research Station ($32.07^{\circ}N$, $125.10^{\circ}E$, 36 m above sea level) during June 2003 and May 2005. Over the 2-year period, the mean ozone concentration was $49.5{\pm}15.5\;ppbv$. Ozone concentrations show great variability with a monthly mean up to 68.2 ppbv in May 2005 and seasonal variations with being highest in spring and fall, and lowest in summer. However, the amplitude of diurnal variation was less than ${\sim}4\;ppbv$ with a maximum at $3{\sim}4\;p.m.$ and minimum at $7{\sim}8\;a.m.$ HYSPLIT backward air trajectory indicated that the air masses with higher ozone came from the north or northwest and those with lower ozone arrived mainly via southerly or southeasterly. Ozone distributions at Ieodo Ocean Research Station were observed to be significantly impacted by long-range transport and regional scale air circulation.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.6
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• pp.607-623
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• 2000

Major trends of ozone concentration variations in Korea were investigated by using observation data from around 100 stations for the period of 1991∼1997. In addition, important regulating those variations were inferred. Three measures such as the number of days exceeding 80ppb, the 95th percentile of daily maxima, and the annual average concentration were used for the analysis of multi-scale ozone concentration variations. Three areas in the southwest (Sosan, Mokpo, and Cheju) of which monitoring has been operated since 1995 showed the highest annual average concentrations over; this was noted because of the high annual average in the Yosu area in the early 1990s. Large increases in annual average concentrations were observed along the relatively cleaner areas connecting Kangnung and Kwangju(northeast to southwest), in contrast to polluted areas connecting Seoul and Pusan(northeast to southeast). Both the number of exceedance days and the daily maximum concentration were nearly constant in the Greater Seoul Area in spite of interannual flucturations associated with year-to-year changes in air temperature. Within the Greater Seoul Area, all three measures usually showed the same trend; they decreased in the middle and west and increased in the east and northeast. All three measures including the number of exceedance days increased largely at Sillim where the average concentration was high but no exceedance days were recorded in the early 1999s, Nationwide ozone concentration variations appear to be determined by the competitive influence of long-range transport and local urban emissions, Within the city including the Greater Seoul Area, changes in emission which accompany changes in population and in the number if vehicles ( in the process of urban development) were found to be important components of ozone concentration variations.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2002.11a
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• pp.343-343
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• 2002

This study examines the influence of long-range transport of dust particles and air pollutants on both local/regional DMS oxidation chemistry and the distribution of sulfur compounds at Jeju Island (33.17$^{\circ}$ N. 126.10$^{\circ}$ E) during the Asian dust-storm(ADS) period in April 2001. The atmospheric concentrations of these sulfur species were measured at a ground station on Jeju Island. Korea as Part of the ACE-Asia intensive operation. Three ADS events were observed during the periods of 10-12, 13-14. and 25-26 April. respectively. The concentrations of DMS and CS$_2$ were higher during the ADS period than during the non-Asian-dust-storm (NADS) period. Conversely. a difference in SO$_2$ levels during the ADS period was not distinguishable from those during the NADS period. The diurnal variation pattern of DMS observed was largely different from that in the remote marine boundary layer. DMS loss by NO$_3$ in the atmospheric boundary layer was dominant due to significantly high NOx levels influenced by the long-range transport of pollutants from East Asia to Jeju Island The DMS maximum during the ADS period was observed in the late afternoon. The oceanic fluxes of DMS during the ADS and NADS periods were estimated to be 5.7$\pm$2.3 and 2.9 (+2.8/-1.5) mole m$^{-2}$ day$^{-1}$ . respectively. The contribution of oxidized DMS to SO$_2$ levels at Jeju Island during the study period was found to be insignificant.

• Journal of Environmental Science International
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• v.4 no.1
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• pp.63-70
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• 1995

Continuous measurements of ground-level ozone (O3) were made in five minutes intervals in the rural area of Korea from July 1993 to June 1994. This site is located in Chongwon, near latitude 36.4$^{\circ}$N, longitude 127.6$^{\circ}$E. The results show that the one-year mean value was 17 ppb, and monthly mean ranged from 6 to 47 ppb. A pronounced maximum in summer and a minimum in winter were found, and these were related to anthropogenic emission and photochemical reaction. Diurnal variations of ozone minimum at 07:00 - 08:00. During the period when ozone concentration was very high (> 80 ppb), the stable winds were from N and UW; on the other hand, when ozone concentration was very low, air movement in the large scale was from the North Pacific Ocean. This suggests that in the rural area the long range transport of anthropogenic pollutants from distant sources can contribute to the larger contribution than the generation of ozone from local sources in the rural area.

• Atmosphere
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• v.32 no.2
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• pp.119-133
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• 2022

From 2015 to 2021, high-concentration fine dust episodes with a daily average PM_2.5 concentration of 50 ㎍ m^-3 or higher were selected and classified into 3 types [long range transport (LRT), mixed (MIX) and Local emission and stagnant (LES)] using synoptic chart and backward trajectory analysis. And relationships between the fine particle data (PM_2.5 and PM₁₀ concentration and PM_2.5/PM₁₀ ratio) and meteorological data (PBLH, Ta, WS, U-wind, and Rainfall) were analyzed using hourly observation for the classification episodes on the Korean Peninsula and the Seoul metropolitan area (SMA). In LRT, relatively large particles such as dust are usually included, and in LES, fine particle is abundant. In the Korean peninsula, the rainfall was relatively increased centered on the middle and western coasts in MIX and LES. In the SMA, wind speed was rather strong in LRT and weak in LES. In LRT, rainfall was centered in Seoul, and in MIX and LES, rainfall appeared around Seoul. However, when the dust cases were excluded, the difference between the LRT and other types of air quality was decreased, but the meteorological variables (Ta, RH, Pa, PBLH, etc.) were further strengthened. In the case of the Korean Peninsula, it is difficult to find a clear relationship because regional influences (topographical elevation, cities and coasts, etc.) are complexly included in a rather wide area. In the SMA, it is analyzed that the effects of urbanization such as the urban heat island centered on Seoul coincide with the sea and land winds, resulting in a combination of high concentrations and meteorological phenomena.