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Haze pollution is affected by local air pollutants, regional transport of background particles and precursors, atmospheric chemistry related to secondary aerosol formation, and meteorological conditions conducive to physical, dynamical, and chemical processes. In the large, populated and industrialized areas like the Asian continental outflow region, the combination of regional transport and local stagnation often exacerbates urban haze pollution. However, the detailed chemical processes underlying the enhancement of urban haze induced by the combined effect of local emissions and transported remote pollutants are still unclear. Here, we demonstrate an important role of transported hygroscopic particles in increasing local inorganic aerosols, by studying the chemical composition of PM 2.5 collected between October 2012 and June 2014 in Seoul, a South Korean megacity in the Asian continental outflow region, using the ISORROPIA II thermodynamic model. PM 2.5 measured under the condition of regional transport from the upwind source areas in China was higher in mass concentration and richer in secondary inorganic aerosol (SIA) species (SO42- , NO3- , and NH4+) and aerosol liquid water (ALW) compared to that measured under non-transport conditions. The secondary inorganic species and ALW were both increased, particularly in cases with high PM 2.5 levels, and this indicates inorganic species as a major driver of hygroscopicity. We conclude that the urban haze pollution in a continental outflow region like Seoul, particularly during the cold season, can be exacerbated by ALW in the transported particles, which enhances the nitrate partitioning into the particle phase in NOx - and NH3 -rich urban areas. This study reveals the synergistic effect of remote and local sources on urban haze pollution in the downwind region and provides insight into the nonlinearity of domestic and foreign contributions to receptor PM 2.5 concentrations in numerical air quality models. [ABSTRACT FROM AUTHOR]

Together with emissions of air pollutants and precursors, meteorological conditions play important roles in local air quality through accumulation or ventilation, regional transport, and atmospheric chemistry. In this study, we extensively investigated multi-timescale meteorological effects on the urban air pollution using the long-term measurements data of PM10, SO2, NO2, CO, and O3 and meteorological variables over the period of 1999-2016 in Seoul, South Korea. The long-term air quality data were decomposed into trend-free short-term components and long-term trends by the Kolmogorov-Zurbenko filter, and the effects of meteorology and emissions were quantitatively isolated using a multiple linear regression with meteorological variables. In terms of short-term variability, intercorrelations among the pollutants and meteorological variables and composite analysis of synoptic meteorological fields exhibited that the warm and stagnant conditions in the migratory high-pressure system are related to the high PM10 and primary pollutant, while the strong irradiance and low NO2 by high winds at the rear of a cyclone are related to the high O3. In terms of long-term trends, decrease in PM10 (-1.75µgm-3yr-1) and increase in O3 (+0.88ppbyr-1) in Seoul were largely contributed by the meteorology-related trends (-0.94µgm-3yr-1 for PM10 and +0.47ppbyr-1 for O3), which were attributable to the subregional-scale wind speed increase. Comparisons with estimated local emissions and socioeconomic indices like gross domestic product (GDP) growth and fuel consumptions indicate probable influences of the 2008 global economic recession as well as the enforced regulations from the mid-2000s on the emission-related trends of PM10 and other primary pollutants. Change rates of local emissions and the transport term of long-term components calculated by the tracer continuity equation revealed a decrease in contributions of local emissions to the primary pollutants including PM10 and an increase in contributions of local secondary productions to O3. The present results not only reveal an important role of synoptic meteorological conditions on the episodic air pollution events but also give insights into the practical effects of environmental policies and regulations on the long-term air pollution trends. As a complementary approach to the chemical transport modeling, this study will provide a scientific background for developing and improving effective air quality management strategy in Seoul and its metropolitan area. [ABSTRACT FROM AUTHOR]

ABSTRACT Youn, D. and Park, Y.H., 2018. The Application of Mathematical Analysis to Examine the Beach Erosion along the Upper Texas Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 846–850. Coconut Creek (Florida), ISSN 0749-0208. The upper Texas coast has been severely damaged by repeated beach erosion without any landfall of tropical storm. Since the average wave height was lower than 1.5 m and the mean tide range was smaller than 0.5 m there, they were not enough to explain the extreme erosion along the coast. Many studies had been conducted to find the causes of continuous erosion and then overwash was suspected by morphological analysis. The past studies, through the analysis of the observation data, concluded that the impact of remote storm might be a major cause of coastal erosion. The Texas Land Office has developed a master plan for coastal resilience and they switched to recovery from investigation. However, beach erosion is still a complicated process and continuous erosion has not been studied until now. For that reason, we here propose an alternative way for the further examination. A mathematical approach called as Empirical Orthogonal Function (EOF) is chosen to analyze spatiotemporal variations. We here applied the EOF method to the observed beach profile data to examine the spatiotemporal characteristics of waves related to the erosion problem. During the observation, the landfall of hurricane was made in the study area and it would be an interesting analysis of affected or unaffected beach change by storm. The short and long-term variations by landfall of storm or impact of remote storm were also studied by EOF method respectively. The dominance of cross-shore process such as overwash was also analyzed in this study. [ABSTRACT FROM AUTHOR]

Youn, D. and Park, Y.H., 2018. The Application of Mathematical Analysis to Examine the Beach Erosion along the Upper Texas Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 846–850. Coconut Creek (Florida), ISSN 0749-0208. The upper Texas coast has been severely damaged by repeated beach erosion without any landfall of tropical storm. Since the average wave height was lower than 1.5 m and the mean tide range was smaller than 0.5 m there, they were not enough to explain the extreme erosion along the coast. Many studies had been conducted to find the causes of continuous erosion and then overwash was suspected by morphological analysis. The past studies, through the analysis of the observation data, concluded that the impact of remote storm might be a major cause of coastal erosion. The Texas Land Office has developed a master plan for coastal resilience and they switched to recovery from investigation. However, beach erosion is still a complicated process and continuous erosion has not been studied until now. For that reason, we here propose an alternative way for the further examination. A mathematical approach called as Empirical Orthogonal Function (EOF) is chosen to analyze spatiotemporal variations. We here applied the EOF method to the observed beach profile data to examine the spatiotemporal characteristics of waves related to the erosion problem. During the observation, the landfall of hurricane was made in the study area and it would be an interesting analysis of affected or unaffected beach change by storm. The short and long-term variations by landfall of storm or impact of remote storm were also studied by EOF method respectively. The dominance of cross-shore process such as overwash was also analyzed in this study. [ABSTRACT FROM AUTHOR]

We examine the meteorological responses due to the probable eruption of Mt. Baekdu using an off-line Climate-Chemistry model that is composed of the National Center for Atmospheric Research (NCAR) Climate Atmosphere Model version 3 (CAM3) and a global chemistry transport model (GEOS-Chem). Using the aerosol dataset from the GEOS-Chem driven by GEOS-5 meteorology, experiment and control simulations of the climate model are performed and their meteorological differences between the two simulations are analyzed. The magnitudes of volcanic eruption and column injection height were presumably set to 1/200 of the Mt. Pinatubo eruption and 9 km, respectively. Significant temperature drop in the lower troposphere (850 hPa), which is mainly due to a direct effect of prescribed volcanic aerosols from Mt. Baekdu, has been simulated up to about −4 K. The upper atmosphere (150 hPa) right above the volcano, however, shows significant warming due to the absorption of the infrared radiation by volcanic aerosols. As a result of the volcanic eruption in the climate model, wave-like patterns are shown in both the geopotential height and horizontal wind. The changes in the lower atmospheric temperature are well associated with the modification of the atmospheric circulation through the hydrostatic balance. In spite of limitations in our current simulations due to several underlying assumptions, our results could give a clue to understanding the meteorological impacts from Mt. Baekdu eruptions that are currently attracting considerable public attention. [ABSTRACT FROM AUTHOR]

Youn, D. and Park, Y.H., 2021. Climate change: Characteristics of storms around Korea. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 256–260. Coconut Creek (Florida), ISSN 0749-0208. Many studies have shown that the intensity and frequency of storms are increasing due to global warming. Because storms are affected by many factors, such as the climate and sea, the relationships of some factors still need to be studied for better understanding. Most recent storm studies have focused on increasing the accuracy of numerical model simulations; however, this study employs statistical methods to find the correlation among factors that determined storm characteristics. Correlation analysis was conducted using certain factors in the ocean and atmosphere. The analysis was conducted using R software for statistical computing of the selected storms passing near the Korean Peninsula, considering the difficulty of storm study. Typhoons occurring in the last 40 years were analyzed, and the relationships of many variables were calculated. The number of typhoons heading for Korea has increased, but the increment of their intensity was not apparent in the observational data. Unlike previous methods, this work was conducted for typhoons that passed through a defined area on the southern coast of the Korean Peninsula. In the region between 30° and 35° N, typhoon paths changed to move northeast instead of being dominated by the Westerlies. Typhoons starting at lower latitudes and more easterly locations tend to develop into strong typhoons, and typhoons starting at lower latitudes tend to be larger. [ABSTRACT FROM AUTHOR]

Park, Y.H. and Youn, D., 2021. Characteristics of storm surge based on the forward speed of the storm. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 71–75. Coconut Creek (Florida), ISSN 0749-0208. Storm surge is determined by the attributes of the storm and several other factors. The forward speed of a storm is known to increase the wave height, but its effect on storm surges has not yet been studied in detail. This study focused on the forward speed of storms approaching the Korean Peninsula, which has been getting slower due to climate change. The forward speed continued to change along the track of the storm until extinction. Despite the difficulties caused by the changes in the moving direction and forward speed of storms, this study investigates the effects of their forward speed on the storm surge using the ADCIRC numerical model. Variations in storm surge due to the forward speed of real and virtual storms were studied by simplifying the other factors. Many test simulations were conducted under various conditions, such as steady and accelerated forward speeds and routes along an artificial straight track of the storm. The results were analyzed to determine the characteristics of the storm surge in terms of forward speed. Some of these were compared with actual cases. Based on the model results, it was found that the forward speed of the storm was inversely proportional to the duration of the storm, and their ratios produced different forms of storm surges. When the forward speed decreases, a storm surge is induced for a longer time. The results also showed that the maximum storm surge increased as the forward speed increased. [ABSTRACT FROM AUTHOR]

Park, Y.H. and Youn, D., 2020. The study of a new tidal power for a practical use. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1500–1504. Coconut Creek (Florida), ISSN 0749-0208. Dynamic Tidal Power (DTP), a kind of tidal power was first developed 20 years ago but it has never been actually built. Because DTP generates power using the diffraction effect of tides, it requires very long and large structures considering tidal period. Economic feasibility is most demanded for a practical use and various studies have been conducted to increase its output. Different shape and length DTPs had been tested in a previous study but they were not economical. For this reason, other ways were simulated to increase power generation in the study. Multiple and slit-type DTPs were chosen. It was found that the proper spacing between DTP structures was necessary for efficient power generation considering tidal diffraction effect. Because the intensity of light is varied as it passes through a single slit, a slit-type DTP was analyzed. The result from a slit-type DTP was failed to improve capacity but it was similar to those of a straight DTP. Because a slit-type DTP required less structure, it would be more economical and environmentally friendly. The study area was located in the west central coast of Korea where the tidal range was the largest and water depth was shallow. The simulations were conducted by the two dimensional numerical model ADCIRC. [ABSTRACT FROM AUTHOR]