• Korean Journal of Remote Sensing
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• v.29 no.2
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• pp.235-241
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• 2013

$NO_2$ vertical column densities were retrieved via ground based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements for the first time for 6 months over the spring season in 2007 and 2008 in Seoul, one the megacities in the Northeast Asia. The retrieved $NO_2$ vertical column densities were compared with those obtained from space borneOzone Monitoring Instrument (OMI). Over the entire measurement period, the $NO_2$ vertical column densities measured by MAX-DOAS ranged from $1.0{\times}10^{15}molec{\cdot}cm^{-2}$ to $6.0{\times}10^{16}molec{\cdot}cm^{-2}$ while those obtained by OMI ranged $1.0{\times}10^{15}molec{\cdot}cm^{-2}$ to $7.0{\times}10^{16}molec{\cdot}cm^{-2}$. The correlation coefficient between $NO_2$ vertical column densities obtained from MAX-DOAS and OMI is 0.73 for the entire measurement period whereas the correlation coefficient of 0.85 is found for the dates under the clear sky condition. The cloudy condition is thought to play a major role in increase in uncertainty of the retrieved OMI $NO_2$ vertical column densities since air mass factor may induce high uncertainty due to the lack of cloud and aerosol vertical distribution information.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2002.11a
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• pp.255-258
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• 2002

The vertical exchange of trace gases and aerosols in upper regions of the atmosphere is primarily controlled by the atmospheric conditions. The study of the vertical and temporal variation of the upward transport of $H_2O$ and the downward transport of $O_3$, NO$_2$, CO and other long-lived trace species will enable a better understanding of these transport mechanisms. (omitted)

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2217-2221
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• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical tube have been investigated by experiment. Before the test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. A smooth tube with outer diameter of 5 mm and length of 1.44 m was selected as a test tube. The test was conducted at mass fluxes of 212 to 530 kg/$m^2s$, saturation temperature of -5 to 20$^{\circ}C$, and heat fluxes of 20 to 45 kW/$m^2$. As the vapor quality and mass fluxes increase, the heat transfer coefficients of carbon dioxide are decreased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.247-251
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• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical micro-fin tube have been investigated by experiment. Before a test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. The micro-fin tube with outer diameter of 5 mm and length of 1.44 m was selected as the test section. The test was conducted at mass fluxes of 318 to $530\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat fluxes of 15 to $30\;kW/m^2$. As the vapor quality increases, the heat transfer coefficients of carbon dioxide are increased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase, and there was not much of influence of mass flux on the heat transfer coefficients.

• Journal of Environmental Health Sciences
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• v.31 no.3
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• pp.215-220
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• 2005

The atmospheric transportation and dispersion processes of air pollutants are important issues in dealing with air pollution problems. Air pollutants originated from biological and anthropogenic activities are not only limited to the local emission sources, but could also be transported and dispersed to other regions by synoptic weather systems. Besides, the complexity of topography of central Taiwan helps accumulating air pollutants to promote high-concentration episodes. The techniques of tethersonding were applied to monitor the vertical profiles of winds, air temperatures and humidity, as well as to collect air samples, to be analyzed for pollutants $(O_3,\;NO_2,\;NO\;and\; NMHC)$ from the ground up to 1000m. A time period of about one week, 19-26 October 2002, was chosen as the sampling period due to the high frequency of episode occurrence in autumn based on the past records. Associating with the analysis of weather patterns, the atmospheric characteristics over high-concentration areas can be resolved in more detail. The result of the tethersonding studies showed that weak northerly sea breeze (with thickness about 300m) with low wind speed (about 1 to 2 m/sec) could help develop high ozone concentrations in the down-wind areas. It is also important to have a built-up aloft of precursors and ozone to develop high concentration on the previous day.

• Proceedings of the Korean Environmental Health Society Conference
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• 2005.06a
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• pp.184-210
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• 2005

The atmospheric transportation and dispersion processes of air pollutants are important issues in dealing with air pollution problems. Air pollutants originated from biological and anthropogenic activities are not only limited to the local emission sources, but could also be transported and dispersed to other regions by synoptic weather systems. Besides, the complexity of topography of central Taiwan helps accumulating air pollutants to promote high-concentration episodes. The techniques of tethersonding were applied to monitor the vertical profiles of winds, air temperatures and humidity, as well as to collect air samples, to be analyzed for pollutants ($O_3,\;NO_2$, NO and NMHC) from the ground up to 1000 m. A time period of about one week, 19 -26 October 2002, was chosen as the sampling period due to the high frequency of episode occurrence in autumn based on the past records. Associating with the analysis of weather patterns, the atmospheric characteristics over high-concentration areas can be resolved in more detail. The result of the tethersonding studies showed that weak northerly sea breeze (with thickness about 300 m) with now wind speed (about 1 to 2 m/sec) could help develop high ozone concentrations in the down-wind areas. It is also important to have a built-up aloft of precursors and ozone to develop high concentration on the previous day.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.6
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• pp.791-804
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• 2011

Numerical simulations were carried out to investigate the impact of PBL (Planetary boundary layer) scheme implemented in WRF on the result of meteorological fields and CMAQ modeling. 25-day period, representing high ozone concentration, was selected for the simulations. The three WRF domains covered East Asia region, Korean Peninsula and Seoul metropolitan area. The sensitivity of WRF-CMAQ modeling to the various PBL schemes was assessed and quantified by comparing model output and against observation from the meteorological and the air quality monitoring network within the domain. The meteorological variables evaluated included temperature, wind speed and direction over surface sites and upper air sounding sites. The CMAQ variables included gaseous species $O_3$ and $NO_x$ over monitoring stations. Although difference of PBL schemes implemented in WRF, they did not appreciably affect the WRF and CMAQ performance. There are partially differences between non-local and local mixing scheme, but are not distinct differences for the results of weather and air quality. It is suggested that impact of parameterization of vertical eddy diffusivity scheme in CMAQ also need to be researched in the future study.

• Journal of Environmental Science International
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• v.26 no.5
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• pp.621-638
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• 2017

Meteorological characteristics related to variations in ozone ($O_3$) concentrations in the Korean peninsula before, during, and after Typhoon Talas (1112) were analyzed using both observation data and numerical modeling. This case study takes into account a high $O_3$ episode (e.g., a daily maximum of ${\geq}90ppb$) without rainfall. Before the typhoon period, high $O_3$ concentrations in the study areas (e.g., Daejeon, Daegu, and Busan) resulted from the combined effects of stable atmospheric conditions with high temperature under a migratory anticyclone (including subsiding air), and wind convergence due to a change in direction caused by the typhoon. The $O_3$ concentrations during the typhoon period decreased around the study area due to very weak photochemical activity under increased cloud cover and active vertical dispersion under a low pressure system. However, the maximum $O_3$ concentrations during this period were somewhat high (similar to those in the normal period extraneous to the typhoon), possibly because of the relatively slow photochemical loss of $O_3$ by a $H_2O+O(^1D)$ reaction resulting from the low air temperature and low relative humidity. The lowest $O_3$ concentrations during the typhoon period were relatively high compared to the period before and after the typhoon, mainly due to the transport effect resulting from the strong nocturnal winds caused by the typhoon. In addition, the $O_3$ increase observed at night in Daegu and Busan was primarily caused by local wind conditions (e.g., mountain winds) and atmospheric stagnation in the wind convergence zone around inland mountains and valleys.

• Asian Journal of Atmospheric Environment
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• v.8 no.3
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• pp.162-174
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• 2014

An abnormal decrease in ozonesonde sensor signal occurred during air-pollution study campaigns in November 2011 and March 2012 in Mexico City Metropolitan Area (MCMA). Sharp drops in sensor signal around 5 km above sea level and above were observed in November 2011, and a reduction of signal over a broad range of altitude was observed in the convective boundary layer in March 2012. Circumstantial evidence indicated that $SO_2$ gas interfered with the electrochemical concentration cell (ECC) ozone sensors in the ozonesonde and that this interference was the cause of the reduced sensor signal output. The sharp drops in November 2011 were attributed to the $SO_2$ plume from Popocat$\acute{e}$petl volcano southeast of MCMA. Experiments on the response of the ECC sensor to representative atmospheric trace gases showed that only $SO_2$ could cause the observed abrupt drops in sensor signal. The vertical profile of the plume reproduced by a Lagrangian particle diffusion simulation supported this finding. A near-ground reduction in the sensor signal in March 2012 was attributed to an $SO_2$ plume from the Tula industrial complex north-west of MCMA. Before and at the time of ozonesonde launch, intermittent high $SO_2$ concentrations were recorded at ground-level monitoring stations north of MCMA. The difference between the $O_3$ concentration measured by the ozonesonde and that recorded by a UV-based $O_3$ monitor was consistent with the $SO_2$ concentration recorded by a UV-based monitor on the ground. The vertical profiles of the plumes estimated by Lagrangian particle diffusion simulation agreed fairly well with the observed profile. Statistical analysis of the wind field in MCMA revealed that the effect Popocat$\acute{e}$petl was most likely to have occurred from June to October, whereas the effect of the industries north of MCMA, including the Tula complex, was predicted to occur throughout the year.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.21 no.1
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• pp.31-46
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• 1993

A radiative transfer model with two-stream/delta-Eddington approximation has been developed to calculate the vertical distributions of atmospheric heating rates and radiative fluxes. The performance of the model has been evaluated by comparison with the results of ICRCCM (Intercomparison of radiative codes in climate models). It has been demonstrated that the presented model has a capability to calculate the solar radiation not only accurately but also economically. The characteristics of ultraviolet-B radiation (UV-B; 280-320nm) are examined by comparison of relation between the flux at the top of atmosphere and that at the surface. The relation of UV-B is quadratic due to the strong ozone absorption in this band. Also, the dependence of the UV-B radiation on the stratospheric ozone depletion and stratospheric aerosol haze due to volcanic eruption on the stratospheric ozone depletion and stratospheric aerosol haze due to volcanic eruption has been tested with various solar zenith angles. The surface UV-B increases as the solar zenith angle increases. The existence of stratospheric aerosols causes an increase in the planetary albedo due to the aerosols' backscattering. The planetary albedo with aerosol's effect has been increases as the solar zenith angle is not sensitive. It may be caused by the fact that the aerosols' scattering effect becomes saturated with the relatively long path length in a large solar zenith angle. Finally, the regional impact of stratospheric aerosols due to volcanic eruption on the intensity of UV-B radiation at the surface has been estimated. A direct effect is that the flux is diminished at the low latitudes, while it is enhanced in the high latitudes by the aerosols' photon trap or twilight effect. In the high latitudes, both aerosols' scattering and ozone absorption have strong and opposite impacts to the surface UV-B radiation is located at the mid-latitudes during spring season in both hemispheres.