• Atmosphere
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• v.25 no.4
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• pp.659-667
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• 2015

In this study, sensitivity of inflow wind speed and turbulent Schmidt number to pollutant dispersion in an urban street canyon is investigated, by comparing CFD-simulated results to wind-tunnel results. For this, we changed systematically inflow wind speed at the street-canyon height ($1.5{\sim}10.0m\;s^{-1}$ with the increment of $0.5m\;s^{-1}$) and turbulent Schmidt number (0.2~1.3 with interval of 0.1). Also, we performed numerical experiments under the conditions that turbulent Schmidt numbers selected with the magnitude of mean kinetic energy at each grid point were assigned in the street canyon. With the increase of the inflow wind speed, the model underestimated (overestimated) pollutant concentration in the upwind (downwind) side of the street canyon because of the increase of pollutant advection. This implies that, for more realistic reproduction of pollutant dispersion in urban street canyons, large (small) turbulent Schmidt number should be assigned for week (strong) inflow condition. In the cases of selectively assigned turbulent Schmidt number, mean bias remarkably decreased (maximum 60%) compared to the cases of constant turbulent Schmidt number assigned. At week (strong) inflow wind speed, root mean square error decreases as the area where turbulent Schmidt number is selectively assigned becomes large (small).

• Journal of the Korean earth science society
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• v.41 no.4
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• pp.344-355
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• 2020

Tropical cyclone scale vortices and associated Rossby waves were investigated numerically using high-resolution barotropic models on the global domain. The equations of the barotropic model were discretized using the spectral transform method with the spherical harmonics function as orthogonal basis. The initial condition of the vortex was specified as an axisymmetric flow in the gradient wind balance, and four types of basic zonal states were employed. Vortex tracks showed similar patterns as those on the beta-plane but exhibited more eastward displacement as they moved northward. The zonal-mean flow appeared to control not only the west-east translation but also the meridional translation of the vortex. Such a meridional influence was revealed to be associated with the beta gyre and the Rossby wave, which are formed around the vortex due to the beta effect. In the case of the basic zonal state of climatological mean, the meridional translation speed reached the maximum value when the vortex underwent recurving.

• Journal of the Korean earth science society
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• v.25 no.2
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• pp.87-93
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• 2004

To study the effect of cloud on the variabilities of turbulent fluxes over the flat terrain, we used the gradient method to analyze the dynamic and thermodynamic data from the meteorological 9-m mast (0.75, 3 and 9 m) in Villafria airport in Spain. The decrease of the surface wind speed is governed by cooling at the surface following the evening transition. The sensible heat flux and the momentum flux are increased with the dynamic factor rather than the thermodynamic factor, and the sensible heat flux was not affected by the thermal condition. The global radiation did not play an important role in the variation of the sensible heat flux in the cloudy day, but the atmospheric surface layer was characterized rather by the wind intensity.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.5
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• pp.604-612
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• 2008

The ozone concentration is one of the important environmental issue for measurement of the atmospheric condition of the country. This study focuses on applying the Autoregressive Error (ARE) model for analyzing the ozone data at middle part of the Gyeonggi-Do, Anyang monitoring site in Korea. In the ARE model, eight meteorological variables and four pollution variables are used as the explanatory variables. The eight meteorological variables are daily maximum temperature, wind speed, amount of cloud, global radiation, relative humidity, rainfall, dew point temperature, and water vapor pressure. The four air pollution variables are sulfur dioxide $(SO_2)$, nitrogen dioxide $(NO_2)$, carbon monoxide (CO), and particulate matter 10 (PM10). The result shows that ARE models both overall and monthly data are suited for describing the oBone concentration. In the ARE model for overall ozone data, ozone concentration can be explained about 71% to by the PM10, global radiation and wind speed. Also the four types of ARE models for high level of ozone data (over 80 ppb) have been analyzed. In the best ARE model for high level of ozone data, ozone can be explained about 96% by the PM10, daliy maximum temperature, and cloud amount.

• Journal of Environmental Science International
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• v.13 no.2
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• pp.167-173
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• 2004

A aqueous solution of malodorants (i.e., n-valeraldehyde, n-valeric- acid, 2-methylisoborneol, and trimethylamine) was exposed to 200KHz ultrasound with a power of 6.0W/$\textrm{cm}^2$ per unit volume in a sonochemical reactor under room temperature and atmospheric pressure condition. The concentration of malodorants decreased with irradiation time, indicating pseudo-first-order kinetics. The removal efficiency of malodorants was about from 50% to 96% decomposed after 90 minutes sonication. At the deodorization, it was determined by triangle odor bag(TOB) method for odor sensory measurement, and it indicated that over 60% of relative odors were deodorized with degradation by the sonication.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.4 no.4
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• pp.263-271
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• 2000

To investigate the distribution of air pollutants dispersion in the horizontal wind fields, a chaff release experiment was carried out by an airplane. The temporal and spatial variations of a chaff plume from an elevated point source using the WSR-88D(NEXRAD) radar. The observed profiles of radar reflectivity were compared with the Gaussian diffusion model at slightly unstable atmospheric condition. The present study shows that the distributions of radar reflectivity from chaffs and their concentration by the model are in general agreement with time variation. The dispersion coefficients in downwind($\sigma$(sub)x) and crosswind($\sigma$(sub)y) spread data exceeded what has generally been found at Pasquill and Brigg\`s estimates. As a result, it was clearly shown that horizontal and vertical diffusion coefficients are more accurately determined as compared with theoretical coefficients. At longer diffusion distances(than 10km), a radar observation provided the determination of maximum range and diffusion height more qualitatively, too.

• Asian Journal of Atmospheric Environment
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• v.6 no.1
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• pp.1-13
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• 2012

To identify the primary factor affected the decreased $PM_{10}$ concentration in Seoul which is the capital city of Korea, wind speed and emissions in 2003 and 2004 were analyzed. The level of air pollution is intense in Seoul and continually increased since the late 1990s. However the concentration of $PM_{10}$ has been greatly declined recently. In particular, the concentration of $PM_{10}$ decreased 14% in 2003 and 2004 excluding the Asian dust periods. It is suggested that the major factors for the decrease are differences in wind speed between the two years and the period of constant breeze. In 2003, intense Asian dust events happened frequently and it increased the concentration of total $PM_{10}$. The intense dust events were influence by the speed and duration of the wind. It is considered that the meteorological condition was the primary drive for the change of the concentration of $PM_{10}$. The decreased emissions seem to be the additional factor for the change in the concentration of $PM_{10}$.

• Journal of Korean Society for Atmospheric Environment
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• v.29 no.2
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• pp.186-198
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• 2013

The present work is an attempt to improve the performance of a regional air quality model by means of liking it with a global chemistry transport model. The global chemical transport model of GEOS-Chem is used to provide BC (Boundary Condition)s which reflect temporal and spatial variations at boundaries of regional chemical transport model of CMAQ over East Asia. First, GEOS-Chem outputs are evaluated by comparing predicted concentrations with observed monthly data of gas phase species and secondary inorganic aerosols from EANET (Acid Deposition Monitoring Network in East Asia) sites. The results show that predicted PM10 concentrations are in good agreement with the observations. This implies that GEOS-Chem outputs could be used to provide BCs to CMAQ. Simulated daily and monthly mean PM10 concentrations of CMAQ with the linkage of GEOS-Chem's BCs and constant BCs are then evaluated by comparing predicted concentrations with observations at API (Air Pollution Index) sites in China as well as EANET sites in Korea. CMAQ with the GEOS-Chem outputs improves model simulation in depicting observed PM10 concentrations comparing with those with constant BCs. It is also found that influence of aerosol species are largely dependent on the BCs over East Asia and Korea. Mean biases between simulated versus observed daily and monthly mean concentrations of PM10 with the GEOS-chem were improved by 1~8 ${\mu}g/m^3$ in China region, 3.26 ${\mu}g/m^3$ in Korea.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.E
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• pp.9-17
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• 1998

Oxides of nitrogen play important roles in atmospheric chemistry. Soil has been recognized as a major natural source of NO, and its emission depends on soil parameters such as soil nitrogen availability, soil moisture and temperature. It is necessary to understand effects of these controlling parameters on soil NO emission. In order to understand soil moisture effects on NO emission, variations of NO concentration and existence of its equilibrium concentration were observed from ammonium fertilized Japanese upland soil prepared for different soil moisture conditions. The closed chamber technique was employed for this study. The significant increases in NO with soil moisture were found. Maximum was occurred at sample ID4 (55% of water-filled pore space (WFPS)), but it decreased as soil moisture increased. No significant NO concentration was emitted from soil sample without fertilizer, but there was significant NO in fertilized soil samples. The magnitudes of NO from soil increased with time and reached at steady state within ten minutes approximately. These results suggest that nitrogen input from fertilizer takes charge in the first step of sharp increase in NO emission, and then soil moisture becomes important factor to control NO emission from the soils. NO concentrations from soil were compared to those one-day after the experiment. Results from the comparison analysis suggest that the soil NO flux might have been stimulated by soil disturbances like mixing, and this is much more effective in dry soils rather than in wet soils. It was found that much less NO came out from soils after a day; suggesting that most of NO was released from the soils within a day after fertilizer application during our experiment. The length of NO releasing time span may depend on the amounts of fertilizer applied, soil moisture condition, and other soil physical parameters.

• Atmosphere
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• v.20 no.1
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• pp.27-35
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• 2010

This study analyzes the climate change in Korea and its impact on the occurrence of forest fire events. The forest fire occurrences in Korea tend to concentrate around large cities. In addition, the spatial distribution of the forest fire occurrence seems to agree with local climate conditions. Though the occurrence of the forest fire shows strong interannual variation, it also exhibits a positive trend. Because the forest fire frequently occurs during early spring, we examined long term climate variability in Korea for the early spring seasons. The climate change in Korea generally has brought warmer, drier, and less precipitable conditions during the early spring. The changes of the atmospheric conditions provide favorable condition for the forest fire. The climate changes in Korea also depict distinct spatial variability according to the atmospheric variables. We compared the regional trend of the fire occurrence with the climate trends. The results show the sharpest growing in the forest fire occurrence over southwest of Korea. This study suggests that the decrease in the precipitation day might affect the sharp increasement of the forest fire occurrence in the southwest of Korea.