• Asian Journal of Atmospheric Environment
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• v.11 no.2
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• pp.114-121
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• 2017

Real-time monitoring of hourly concentrations of atmospheric Radon-222 ($^{222}Rn$, radon) and some gaseous pollutants ($SO_2$, CO, $O_3$) was performed throughout 2013-2014 at Gosan station of Jeju Island, one of the cleanest regions in Korea, in order to characterize their background levels and temporal variation trend. The hourly mean concentrations of radon and three gaseous pollutants ($SO_2$, CO, $O_3$) over the study period were $2216{\pm}1100mBq/m^3$, $0.6{\pm}0.7ppb$, $211.6{\pm}102.0ppb$, and $43.0{\pm}17.0ppb$, respectively. The seasonal order of radon concentrations was as fall ($2644mBq/m^3$)$${\sim_\sim}$$winter ($2612mBq/m^3$)>spring ($2022mBq/m^3$)>summer ($1666mBq/m^3$). The concentrations of $SO_2$ and CO showed similar patterns with those of radon as high in winter and low in summer, whereas the $O_3$ concentrations had a bit different trend. Based on cluster analyses of air mass back trajectories, the air mass frequencies originating from Chinese continent, North Pacific Ocean, and the Korean Peninsula routes were 30, 18, and 52%, respectively. When the air masses were moved from Chinese continent to Jeju Island, the concentrations of radon and gaseous pollutants ($SO_2$, CO, $O_3$) were relatively high: $2584mBq/m^3$, 0.76 ppb, 225.8 ppb, and 46.4 ppb. On the other hand, when the air masses were moved from North Pacific Ocean, their concentrations were much low as $1282mBq/m^3$, 0.24 ppb, 166.1 ppb, and 32.5 ppb, respectively.

• Journal of Korean Society for Atmospheric Environment
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• v.25 no.6
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• pp.550-561
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• 2009

This study is to investigate the air pollution characteristics of an industrialized midsize west-coastal city by comparing air quality to a neighboring inland city. The hourly averaged data of $O_3$, $SO_2$, $NO_2$, CO, and $PM_{10}$ measured from continuous air quality monitoring sites in Gunsan (coastal) and Jeonju (inland) were analyzed. The data set covers the period from 2004 to 2006. The annual average concentrations of the air pollutants in two cities were compared in their abundances and temporal trends as well. $O_3$ and $SO_2$ in Gunsan were relatively higher than those in Jeonju, while vice versa in case of $NO_2$ and $PM_{10}$. It seems that heavy automobile emissions from Jeonju mainly bring on higher $NO_2$ and $PM_{10}$ than those in Gunsan on annual base. $NO_2$ concentrations in both cities showed bimodal diurnal variations with peaks in the morning and in the late evening. These peaks correspond to the coupled effects of rush hour traffic and meteorological conditions (i.e., variation of mixing height and dispersion conditions). Maximum hourly averages of $NO_2$ ranged from 18 ppb to 28 ppb at Jeonju, and from 12 ppb to 20 ppb at Gunsan. $O_3$ showed typical diurnal variation with a maximum in the afternoon between 14:00 and 16:00 LST. Diurnal variations of CO and $PM_{10}$ were similar to $NO_2$ while $SO_2$ was similar to $O_3$. Seasonal variations of $PM_{10}$ in both cities indicated that their concentrations during spring season were significantly high. Asian dust storms occur frequently during spring and seem to affect increase in $PM_{10}$. High $O_3$ and $PM_{10}$ days were selected from both cities. The analyses based on the HYSPLIT trajectory model during the high $O_3$ and $PM_{10}$ showed these episodes (six cases) were mostly coincident with Asian dust storm originated from northern China and Mongolia. However, these high air pollution episodes in the west coastal cities may not only be caused by the Asian dust but also affected by other air pollutants transported from China accompanying the Asian dust.

• Journal of Korea Water Resources Association
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• v.40 no.12
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• pp.943-956
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• 2007

Among various statistics, the spatial correlation function, that is "correlogram", is frequently used to evaluate or design the rain gauge network and to model the rainfall field. The spatial correlation structure of rainfall has the significant variation due to many factors. Thus, the variation of spatial correlation structure of rainfall causes serious problems when deciding the spatial correlation function of rainfall within the basin. In this study, the spatial rainfall structure was modeled using bivariate mixed distributions to derive monthly spatial correlograms, based on Gaussian and lognormal distributions. This study derived the correlograms using hourly data of 28 rain gauge stations in the Keum river basin. From the results, we concluded as following; (1) Among three cases (Case A, Case B, Case C) considered, the Case A(+,+) seems to be the most relevant as it is not distorted much by zero measurements. (2) The spatial correlograms based on the lognormal distribution, which is theoretically as well as practically adequate, is better than that based on the Gaussian distribution. (3) The spatial correlation in July exponentially decrease more obviously than those in other months. (4) The spatial correlograms should be derived considering the temporal resolution(hourly, daily, etc) of interest.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.6
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• pp.412-420
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• 2014

Water quality variations were investigated at 4 locations of Jungrang river (upper, middle and lower basins) during a period of 3 rainfall events. During the rainfall, concentrations of $COD_{Mn}$, SS and $BOD_5$ significantly increased, while the concentration of T-N decreased and that of T-P remained relatively constant. This pattern became more apparent as the level of accumulative precipitation and rainfall intensity increased. Simple regression analysis showed that the accumulative precipitation was positively correlated with all water quality pollutants except for T-N. With increasing accumulative precipitation, the concentration of T-N decreased, while the others increased. $R^2$ of simple regressions of hourly average rainfall intensity and water quality pollutants, showed wider range of variation ranged from 0.483 to 0.992, which indicated a strong correlation. The stronger the hourly average rainfall intensity, the more T-N and T-P in the upper basin, more $COD_{Mn}$ in the middle and lower basins, more SS with gradual increase from upper to lower areas, and more $BOD_5$ with gradual decrease from upper to lower region. Simple regression showed that water quality pollution in the upper basin was more sensitive to an increase of rainfall discharge than that in the middle and lower areas.

• Journal of Environmental Health Sciences
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• v.47 no.6
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• pp.521-529
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• 2021

Background: The coronavirus disease (COVID-19) has caused changes in human activity, and these changes may possibly increase or decrease exposure to fine dust (PM_2.5). Therefore, it is necessary to evaluate the exposure to PM_2.5 in relation to the outbreak of COVID-19. Objectives: The purpose of this study was to compare and evaluate the exposure to PM_2.5 concentrations by the variation of dynamic populations before and after the outbreak of COVID-19. Methods: This study evaluated exposure to PM_2.5 concentrations by changes in the dynamic population distribution in Guro-gu, Seoul, before and after the outbreak of COVID-19 between Jan and Feb, 2020. Gurogu was divided into 2,204 scale standard grids of 100 m×100 m. Hourly PM_2.5 concentrations were modeled by the inverse distance weight method using 24 sensor-based air monitoring instruments. Hourly dynamic population distribution was evaluated according to gender and age using mobile phone network data and time-activity patterns. Results: Compared to before, the population exposure to PM_2.5 decreased after the outbreak of COVID-19. The concentration of PM_2.5 after the outbreak of COVID-19 decreased by about 41% on average. The variation of dynamic population before and after the outbreak of COVID-19 decreased by about 18% on average. Conclusions: Comparing before and after the outbreak of COVID-19, the population exposures to PM_2.5 decreased by about 40%. This can be explained to suggest that changes in people's activity patterns due to the outbreak of COVID-19 resulted in a decrease in exposure to PM_2.5.

• Journal of Korean Society for Atmospheric Environment
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• v.33 no.3
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• pp.251-264
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• 2017

Recently, Jeollabuk-do has been reported as a province where the $PM_{10}$concentration is one of the highest levels in South Korea. To explore the characteristics and origins of the $PM_{10}$in Jeollabuk-do, we present one of the first long-term datasets including a statistical analysis of $PM_{10}$concentrations obtained from six cities in the province from 2010 to 2015. During the entire periods, the mean hourly $PM_{10}$concentration was $49.3{\mu}g/m^3$, which correspond to the annual ambient air quality standards for $PM_{10}$in South Korea, and the annual $PM_{10}$concentration of each city showed a similarity in year-to-year variations. In the monthly variation of $PM_{10}$, the $PM_{10}$concentrations showed a maximum value in May that was one of the top levels among the provinces of Korea while the concentrations were dramatically decreased in August showing one of the lowest levels among the provinces in Korea. For the diurnal variation of $PM_{10}$, the $PM_{10}$concentration was enhanced during the rush hours together with gaseous species of $NO_2$, and CO. When the high concentrations of $PM_{10}$were observed (the highest 10% of the $PM_{10}$mass contribution), temperature and relative humidity were low. Using HYSPLIT backward trajectories and cluster analysis for the high $PM_{10}$concentrations, we found that the pollution plumes were transported mainly from China.

• Environmental Analysis Health and Toxicology
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• v.24 no.3
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• pp.203-211
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• 2009

A lesser degree of research is available with respect to indoor radon characteristics associated with occupants' exposure. The present study evaluated the radon levels in several public-access buildings or underground facilities, and their temporal variation in underground facilities. Radon measurements were conducted in 2005 and 2006, utilizing a continuous radon detector. A solid alpha detector (RAD7) was utilized to measure indoor radon levels. The mean radon concentrations obtained from the building or facilities were in a descending order: platforms of Daegu subway line 2, 2005 (32 $Bq/m^3$), hot-air bathroom (14 $Bq/m^3$), basement of office building (14 $Bq/m^3$), underground parking garage (14 $Bq/m^3$), underground shop (12 $Bq/m^3$), nursery (10 $Bq/m^3$), platforms of Daegu subway line 2, 2006 (9.0 $Bq/m^3$), platforms of Daegu subway line 1, 2006 (8.9 $Bq/m^3$), supermarket (7.9 $Bq/m^3$), hospital (7.3 $Bq/m^3$), and second-floor of office building (5.7 $Bq/m^3$). In general, underground-level facilities exhibited higher radon levels as compared with ground-level facilities. It was suggested that ventilation is an important parameter regarding the indoor levels of a subway. There was a decreasing or increasing trend in hourly-radon levels in a subway, whereas no trend were observed in a basement of office building. In addition, the radon levels in the subway lines 1 and 2 varied according to the platforms. The radon levels in the present study were much lower than those of previous studies. The average annual effective dose (AED) of radiation from indoor radon exposure was estimated to be between 0.043 and 0.242 mSv/yr, depending on facility types. These AEDs were substantially lower than the worldwide average AED (2.4 mSv/yr).

• Journal of the Korean Institute of Gas
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• v.17 no.2
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• pp.78-84
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• 2013

A numerical study on the heat and fluid flow has carried out for the design of the steam reforming reactor which consists of six reforming tubes and one burner. Reforming reaction calculation is coupled with the heat and fluid flow one. The burner type in the reforming reactor is chosen through the fluid flow calculation according to different type of burner structure. It is shown that the significant temperature gradient exists in the reforming reactor, affecting the component variation along the length of reforming tube. The component ratio of reforming gas is changed by the variation of SCR and GHSV.

• Atmosphere
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• v.30 no.1
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• pp.47-57
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• 2020

In this study, the climatological spatio-temporal variation of strong wind and gust wind in Korea during the period from 1993 to 2018 was analyzed using daily maximum wind speed and daily maximum instantaneous wind speed data recorded at 61 observations. Strong wind and gust wind were defined as 14 m s^-1 and 20 m s^-1, which are the same as the KMA's criteria of special weather report. The frequency of strong wind and gust wind occurrence was divided into regions with the higher 25 percent (Group A) and the lower 75 percent (Group B). The annual frequency of strong wind and gust wind occurrence tended to be decreased in most parts of the Korean peninsula. In Group A with stations located at coastal region, strong wind and gust wind occurred most frequently in winter with higher frequency at 1200~1600 LST and 2300~2400 LST due to influence of East Asian winter monsoon. In addition, a marked decreasing trend throughout the four seasons was shown at Daegwallyeong, Gunsan and Wando observations. In contrast, it can be found in Group B that the monthly frequency of strong wind and wind gust occurrence was higher in August and September by effect of typhoon and hourly frequency was higher from 1200 LST to 1800 LST.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.1
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• pp.85-94
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• 2018

For the design of wind-power facilities, the highest and lowest astronomical tides (HAT and LAT, respectively) are needed for the tidal-water levels regarding international designs; however, the approximate highest high water and approximate lowest low water AHHW and ALLW, respectively, have been used in Korea. The HAT and LAT in the wind-farm test-bed sea should be estimated to satisfy the international standard. In this study, the HAT and LAT are therefore estimated using the hourly tidal-elevation data of the Eocheongdo, Anmado, Younggwang, Gunsan, Janghang, and Seocheon tidal-gauging stations that are located in the adjacent coastal sea. The nodal variation patterns of the major lunar components, such as $M_2$, $O_1$, and $K_1$ are analyzed to check the expected long-term lunar cycle, i.e., 18.61 year's nodal-variation patterns. The temporal amplitude variations of the $M_2$, $O_1$, and $K_1$ clearly show the 18.61-years periodic patterns in the case of the no-nodal correction condition. In addition, the suggested HAT and LAT elevations, estimated as the upper and lower confidence limits of the yearly HAT and LAT elevations, are 50 cm greater than the AHHW and 40 cm lower than the ALLW, respectively.