• Atmosphere
• /
• v.30 no.3
• /
• pp.257-276
• /
• 2020

Faithful evaluation of the meteorological input is a prerequisite for a better understanding of air quality model performance. Despite the importance, the preliminary meteorological assessment has rarely been concerned. In this study, we aim to evaluate the performance of the Weather Research and Forecasting (WRF) model conducting a year-long high-resolution meteorological simulation in 2016 over the Seoul metropolitan area. The WRF model was configured based on a series of sensitivity simulations of initial/boundary meteorological conditions, land use mapping data, reanalysis grid nudging method, domain nesting method, and urban canopy model. The simulated results of winds, air temperature, and specific humidity in the atmospheric boundary layer (ABL) were evaluated following statistical evaluation guidance using the surface and upper meteorological measurements. The statistical evaluation results are presented. The model performance was interpreted acceptable for air quality modeling within the statistical criteria of complex conditions, showing consistent overestimation in wind speeds. Further statistical analysis showed that the meteorological model biases were highly systematic with systematic bias fractions (f_SB) of 20~50%. This study suggests that both the momentum exchange process of the surface layer and the ABL entrainment process should be investigated for further improvement of the model performance.

• Atmosphere
• /
• v.30 no.4
• /
• pp.391-404
• /
• 2020

To understand the characteristics of the relationship between visibility and particulate matter (PM) in different meteorological conditions, we investigated the contributions of PM and relative humidity (RH) to visibility in Seoul, South Korea. For the period from 2001 to 2018, both PM and RH show descending trends, resulting in a visibility increase. PM has little impact on the hourly variation of visibility, which could be explained more by the RH variability. Meanwhile, the daily change of PM accounts for daily visibility variation. For the monthly variation of visibility, both PM and RH showed similar influence. The correlation coefficients of PM10, PM2.5, and RH with visibility was -0.486, -0.644, and -0.556, respectively, which became higher during the high PM seasons of spring and winter. The correlation coefficient between PM2.5 and visibility was -0.454 for RH higher than 80%, and -0.780 for RH between 40% and 60%. From 2017 to 2018, there were 10 cases of extreme visibility impairment, among which five cases were incurred by high PM pollution, and two cases were by high humidity. Further analysis with PM chemical composition measurements is required to better understand the characteristics of visibility in Seoul.

• Journal of Korean Society for Atmospheric Environment
• /
• v.22 no.6
• /
• pp.888-903
• /
• 2006

This study analyze the change of wind pattern and intensity according to the transform of surface conditions, such as land use and height of terrain, over the leeward region. In order to do this, we have employed 'Envi-met' microscale atmospheric numerical model. When the same wind condition is considered, the wind speed of base case having natural surface condition of Chunsudae shows the weakest strength among different cases such as the 'bare case' and the '20 m case' which the plants is removed and the height of terrain is flatted as 20 m above the sea level over the Chunsudae, respectively. The weakening of wind speed is a maximum of $4{\sim}8 m/s$ when the inflow wind speed is 55 m/s.

• Journal of Korean Society for Atmospheric Environment
• /
• v.18 no.2
• /
• pp.85-94
• /
• 2002

In this study, a 3-dimensional numerical model, has been developed applied for the investigation of combustion characteristics, and used to optimize operating conditions in MSW incinerator, in Gwangju. The model developed in this study has been verified by exacting both the predicted and the measured temperature in combustion chamber which has been operated to provide a reference condition. By predictive results, the Sangmoo incinerator has a good characteristics of combustion and low emission however after burning zone produced incomplete products, also probably because the supply of primary air was not enough. Parametric screening studies have been conducted to study optimal operating conditions. For the optimal combustion characteristics, operating conditions should be adjusted with the waste properties.

• Journal of Surface Science and Engineering
• /
• v.36 no.3
• /
• pp.272-283
• /
• 2003

Mild steel and zinc specimens were tested in five atmospheric testing sites of Vietnam in order to collect the corrosion databank as well as to study the corrosion mechanism in tropical conditions, in period of 1997-2000. The results obtained showed that the corrosion rate of steel is in the range of $10-50\;{\mu}m/year$ and of zinc is of $1-5\;{\mu}m/year$. They are interpretable in the comparison with the data obtained in different countries in the South East Asian as well as previous reports of Vietnamese nation project In atmospheric corrosion. The main factors affecting the corrosion in Vietnam tropical conditions are TOW (time of wetness) and salinity. The relationship between sulfur dioxide and corrosion of metals, particularly, zinc was not found clearly. An explanation was suggested about the complex effect of different pieces present in tropical atmosphere and about the alternative of the dominant factors such as humidity, salinity or temperature.

• Journal of Korean Society for Atmospheric Environment
• /
• v.9 no.2
• /
• pp.168-173
• /
• 1993

Air quality impacts of point and area sources were analyzed by using ISCST2 with wind speed and stability class combinations of SCREEN. Stack height was important in determining the impact of point sources. With the stack height reduced to 21m from 75m, the concentration in the vicinity increased several times in spite of decreasing the emission rate by half. When the emission rates were same, concentrations from an area source of 10m release height were slightly lower than those from a point source of 21m stack height at the plume centerline. Bur the area source resulted in larger area of high concentration. Concentration from the point source was high in neutral to slightly unstable conditions with strong winds in a short distance, and in stable conditions with weak winds in a long distance. Concentration from the area source decreased with distance from the source, and was high in stable conditions with weak winds.

• Journal of Korean Society for Atmospheric Environment
• /
• v.19 no.E2
• /
• pp.75-81
• /
• 2003

Variational data assimilation, which is recently introduced to the air quality modeling, is a promising tool for obtaining optimal estimates of initial conditions and other important parameters such as emission and deposition rates. In this paper. two advanced techniques for variational data assimilation, based on the adjoint and quasi-inverse methods, are tested for a simple air quality problem. The four-dimensional variational assimilation (4D-Var) requires to run an adjoint model to provide the gradient information in an iterative minimization process, whereas the inverse 3D-Var (I3D-Var) seeks for optimal initial conditions directly by running a quasi -inverse model. For a process with small dissipation, I3D-Vu outperforms 4D-Var in both computing time and accuracy. Hybrid application which combines I3D-Var and standard 4D-Var is also suggested for efficient data assimilation in air quality problems.

• Journal of Environmental Science International
• /
• v.12 no.9
• /
• pp.987-996
• /
• 2003

In this study, we analyzed the relationship between the time-variation trend of air pollution concentration index and the meteorological conditions with CO(carbon monoxide) concentration and meteorological observation data in high-CO episode days. CO is a representative automobile air pollutant. The results are as follows; 1. Most of the high-CO episode days within 30 classes appeared in winter season. 2. Most of them appeared under the surface weather conditions with east-west high-pressure system. The surface winds in this high-pressure area were very light. 3. The high-CO episode days were due to unusual accumulation within urban atmosphere in the morning. 4. The Atmospheric stabilities were more stable, and then the wind-ventilation conditions were worse than yearly mean atmospheric condition in Daegu.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.10
• /
• pp.653-656
• /
• 2014

$Cs_3Sb$ photocathode was formed by newly developed process and successive in-situ lighting devices were fabricated in a process chamber. R, G, and B phosphors were applied on the anode plate, respectively. Major parameters such as brightness, power consumption, and efficacy were measured. The wavelength of LED excitation source was 450 nm. Both high power and low power modes were applied in the measurement. Measurement values were clearly differentiated by the voltage application modes. The measured values of each parameter was good enough to be applied for general lighting source. The results showed that $Cs_3Sb$ photocathode formed in atmospheric conditions was functioning as good as the photocathode formed in UHV conditions, and thus it could be applied to advanced lighting devices.

• Journal of Korean Society for Atmospheric Environment
• /
• v.16 no.2
• /
• pp.141-150
• /
• 2000

In order to genralize the vertical dispersion of plume at long distances on mesoscale over complex terrain dispersion coefficients data have been obtained systematically according to lapsed time after release by using a composite turbulence water tank that simulates convective boundary layer. Dispersion experiments have been carried out for various combined conditions of thermal turbulence intensity mechanical turbulence intensity and plume release height at slightly to moderately unstable conditions. Results of tracer dispersion experiments conducted using water tank camera and image processing system have been converted into atmospheric dispersion data through the application of similarity law. The equation $\sigma$z/Zi=aX/(b+c X2)0.5 where $\sigma$2; vertical dispersion coefficient zi : mixing height X : dimen-sionaless downwind distance was confirmed to be an appropriate and general equation for expressing $\sigma$2 variation with turbulence intensity and plume release height, The value of "a" was found to be principally affected by mechanical turbulence intensity and that of "b" by mechanical turbulence intensity and release height. It was confirmed that the magnitude of "c" varies with release height. Results of water tank experiments on the relationship of $\sigma$2 vs downwind distance x have been compared with actual atmospheric dispersion data such as CONDORS data and Bowne's nomogram Operating conditions of a composite turbulence water tank for simulating the field turbulence situations of CONDORS experiments and Bowne's $\sigma$2(x) nomogram for suburban area have also been investigated in terms of water temperature difference between convection water tank and bottom plate heating tank grid plate stroke mixing water depth length scale and velocity scale. Moreover the effect of mechanical turbulence intensity on vertical dispersion has been discussed in the light of release height and downwind distance. height and downwind distance.