• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
• /
• v.4 no.3
• /
• pp.127-137
• /
• 2000

This study presents an analysis of the characteristics of vertical ozone distribution near the surface using ozonesonde data(l995 to 1998), plus surface ozone and meteorological data from the Pohang region. These features were examined in detail using three case studies. The first related to episodes of high surface ozone concentrations during the Spring season when the frontogenesis between the high and low pressure associated with the upper-level jet stream was found to be located near the surface. The second was a 5-day winter period(l3 -17 December, 1997) in the Pohang province when the hourly concentrations exceeded 90 ppb on several occasions owing to low-level jets(LLJs) induced by a nocturnal stable layer. Accordingly, this explains why the high surface ozone concentrations occurred at night as the ozone was transported across the zone by a strong wind speed( over 12.5 ms .1). The third case study was ozone enhancement due to photochemical reactions. In this case, the maximum concentration of ozone exceeded 60 ppb in the summer(23 -28 August, 1997). When an ozone peak appeared within the boundary layer, the occurrence frequency of a low-level jet due to the nocturnal stable layer was about 77%, similarly the occurrence frequency of a near-surface ozone peak relative to the appearance of an LLJ was about 76%. Accordingly, there is clearly a close correlation between the occurrence of LLJs and near-surface ozone peaks.

• Journal of Korean Society for Atmospheric Environment
• /
• v.9 no.4
• /
• pp.303-309
• /
• 1993

An observational study of urban heat island was carried out using field data obatined during 6 days in May and August 1992 in Chunchon(population size 180.000). Air temperature was measured at 64 points along two sampling ruoutes by themisters attached to cars. Both routes cover urban and rural area and across the cneter of urban area. Continuous observation of air sonde was perfomed to clarify heights of nocturnal boundary layer(NBL) at the center of urban area. Surface meteorological observations were performed at both urban and rural sites. This study showed that heat island phenomena was obviously observed at the urbanized area during the night time with low wind speed. The average NBL heights exteded to about 10 meters, but varied with meteorological conditions. After sunset, the air temperature decreased with time at both sites and cooling rate at the urban site was greater than the rural site. The maximum heat island intensity was 7.5$^{\circ}$C at 21 LST, May 4. Usingthe two meteorological data sets obtained from urban and rural sites, the air pollutant concentration was calculated by Gaussian plume model which can obtain not only horizontal distribution of concentration but also vertical distribution. The result indicated that the concentration resulted from urban meteorological data set was lower than that from rural meteorological data set. It was also calculated that the air pollutant extended to higher level in urban meteorological data set than that in rural meteorological data set.

• Journal of Wetlands Research
• /
• v.8 no.3
• /
• pp.91-103
• /
• 2006

The objective of this study is to analyze the characteristics of flow and bed change at the wide, shallow confluence of the Geum river and Mihocheon, which has different bed slope, height, and sediment concentration condition between the main channel and tributary. RMA-2 and SED2D were used to simulate flow and bed changes at the site. Flow simulations showed that the overall flow velocity, shear layer and vortex generated at the left bank of the confluence increase as the discharge was increased. Sediment transport simulations indicated that because of the high inflow sediment concentration from Mihocheon, sediment concentration in the main river increases after the confluence, the high sediment concentration band was kept along the shear layer boundary and the left bed was aggraded after confluence.

• Corrosion Science and Technology
• /
• v.22 no.4
• /
• pp.297-303
• /
• 2023

This study aimed to evaluate hydrogen permeation behaviors of pre-strained twinning-induced plasticity steel with or without Zn coating using electrochemical permeation technique. In contrast to un-strained and 30% strained samples, permeation current density was measured in the 60% strained sample. Tensile pre-straining at 60% involved microstructural modifications, including a high level of dislocation density and stacking fault with a semi-coherent twin boundary, which might provide a high diffusion path for hydrogen atoms. However, reproducibility of measurements of hydrogen permeation current was low due to non-uniform deformation and localized stress concentration. On the other hand, the permeation current was not measured in pre-strained TWIP steel with Zn coating. Instead, numerous blisters with some cracks were observed on the surface of the coating layer. In locally damaged Zn coating under tensile straining, hydrogen atoms could relatively easily permeate through the coating layer. However, they were trapped at the interface between the coating layer and the substrate, which might delay hydrogen penetration into the steel substrate.

• Asian Journal of Atmospheric Environment
• /
• v.9 no.2
• /
• pp.114-127
• /
• 2015

In the Mexico City Metropolitan Area (MCMA), ozone ($O_3$) concentration is still higher than in other urban areas in developed countries. In order to reveal the current state of photochemical air pollution and to provide data for validation of chemical transport models, vertical profiles of meteorological parameters and ozone concentrations were measured by ozonesonde in two field campaigns: the first one, during the change of season from wet to dry-cold (November 2011) and the second during the dry-warm season (March 2012). Unlike previous similar field campaigns, ozonesonde was launched twice daily. The observation data were used to analyze the production and distribution of ozone in the convective boundary layer. The observation days covered a wide range of meteorological conditions, and various profiles were obtained. The evolution of the mixing layer (ML) height was analyzed, revealing that ML evolution was faster during daytime in March 2012 than in November 2011. On a day in November 2011, the early-morning strong wind and the resulting vertical mixing was observed to have brought the high-ozone-concentration air-mass to the ground and caused relatively high surface ozone concentration in the morning. The amount of produced ozone in the MCMA was estimated by taking the difference between the two profiles on each day. In addition to the well-known positive correlation between daily maximum temperature and ozone production, effect of the ML height and wind stagnation was identified for a day in March 2012 when the maximum ground-level ozone concentration was observed during the two field campaigns. The relatively low ventilation coefficient in the morning and the relatively high value in the afternoon on this day implied efficient accumulation of the $O_3$ precursors and rapid production of $O_3$ in the ML.

• Journal of Soil and Groundwater Environment
• /
• v.29 no.4
• /
• pp.12-20
• /
• 2024

Diffusive gradients in thin films (DGT) are passive sampling devices used to determine the time-weighted average concentrations (TWAC) of contaminants. To ensure accurate performance in groundwater, it is crucial to identify environmental characteristics and maintain optimal operational conditions. This study examined the deployment time required to reach effective capacity, the thickness of the diffusive boundary layer (DBL) under stagnant water conditions, and biofilm formation on the DGT surface using groundwater samples. When using DGT with Chelex gel (A=3.14 cm²), the effective capacity was 0.7 ㎍ for Cd and 250 ㎍ for Zn, with a deployment time of 24 h. Lower Cd accumulation was due to the competition effect of coexisting ions. The DBL thickness under stagnant conditions was 0.074 cm, 93% of the diffusion gel's thickness (0.08 cm). Neglecting DBL thickness in TWAC calculations led to a 79% decrease in the determined concentration. No biofouling was observed during the 28-d DGT deployment in groundwater. In conclusion, it is essential to consider the appropriate deployment time, DBL thickness, and biofilm formation to ensure accurate DGT performance in determining contaminant levels in groundwater.

• Journal of the Korean Ceramic Society
• /
• v.34 no.2
• /
• pp.131-138
• /
• 1997

Silicon carbide films were chemically vapor deposited onto graphite substrates using MTS(Ch3SiCl3) as a source and Ar or H2 as a diluent gas. The experiments were performed at a fixed condition such as a de-position temperature of 130$0^{\circ}C$, a total pressure of 10 torr, and a flow rate of 100 sccm for each MTS and carrier gas. The purpose of this study is to consider the variation of the growth behavior with the addition of each diluent gas. It is shown that the deposition rate leads to maximum value at 200 sccm addition ir-respective of diluent gases and the deposition rate of Ar addition is faster than that of H2 one. It seems that these characteristics of deposition rate are due to varying interrelationship between boundary layer thick-ness and the concentration of a source with each diluent gas addition, when overall deposition rate is con-trolled by mass transport kinetics. The preferred orientation of (220) plane was maintained for the whole range of Ar addition. However, above 200 sccm addition, especially that of (111) plane was more increased in proportion to H2 addition. Surface morphologies of SiC films were the facet structures under Ar addition, but those were gradually changed from facet to smooth structures with H2 addition. Surface roughness be-came higher in Ar, but it became lower in H2 with increasing the amount of diluent gas.

• Journal of Environmental Science International
• /
• v.11 no.5
• /
• pp.419-436
• /
• 2002

The current paper reports on the enhancement of O$_3$, CO, NO$_2$, and aerosols during the Asian dust event that occurred over Korea on 1 May 1999. To confirm the origin and net flux of the O$_3$, CO, NO$_2$, and aerosols, the meteorological parameters of the weather conditions were investigated using Mesoscale Meteorological Model 5(MM5) and the TOMS total ozone and aerosol index, the back trajectory was identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory Model(HYSPLIT), and the ozone and ozone precursor concentrations were determined using the Urban Ashed Model(UAM). In the presence of sufficiently large concentrations of NO$\sub$x/, the oxidation of CO led to O$_3$ formation with OH, HO$_2$, NO, and NO$_2$ acting as catalysts. The sudden enhancement of O$_3$, CO, NO$_2$ and aerosols was also found to be associated with a deepening cut-off low connected with a surface cyclone and surface anticyclone located to the south of Korea during the Asian dust event. The wave pattern of the upper trough/cut-off low and total ozone level remained stationary when they came into contact with a surface cyclone during the Asian dust event. A typical example of a stratosphere-troposphere exchange(STE) of ozone was demonstrated by tropopause folding due to the jet stream. As such, the secondary maxima of ozone above 80 ppbv that occurred at night in Busan, Korea on 1 May 2001 were considered to result from vertical mixing and advection from a free troposphere-boundary layer exchange in connection with an STE in the upper troposphere. Whereas the sudden enhancement of ozone above 100 ppbv during the day was explained by the catalytic reaction of ozone precursors and transport of ozone from a slow-moving anticyclone area that included a high level of ozone and its precursors coming from China to the south of Korea. The aerosols identified in the free troposphere over Busan, Korea on 1 May 1999 originated from the Taklamakan and Gobi deserts across the Yellow River. In particular, the 1000m profile indicated that the source of the air parcels was from an anticyclone located to the south of Korea. The net flux due to the first invasion of ozone between 0000 LST and 0600 LST on 1 May 1999 agreed with the observed ground-based background concentration of ozone. From 0600 LST to 1200 LST, the net flux of the second invasion of ozone was twice as much as the day before. In this case, a change in the horizontal wind direction may have been responsible for the ozone increase.

• Asian Journal of Atmospheric Environment
• /
• v.9 no.4
• /
• pp.259-271
• /
• 2015

This study conducted analyses on biogenic volatile organic compounds (BVOC) emission sources contributing to urban ozone ($O_3$) concentration in Osaka Prefecture, Japan in summer 2010 by using the Weather Research and Forecasting model (WRF) version 3.5.1 and the Community Multiscale Air Quality model (CMAQ) version 5.0.1. This prefecture is characterized by highly urbanized area with small forest area. The contributions of source regions surrounding Osaka were estimated by comparing the baseline case and zero-out cases for BVOC emissions from each source region. The zero-out emission runs showed that the BVOC emissions substantially contributed to urban $O_3$ concentration in Osaka (10.3 ppb: 15.9% of mean daily maximum 1-h $O_3$ concentration) with day-by-day variations of contributing source regions, which were qualitatively explained by backward trajectory analyses. Although $O_3$ concentrations were especially high on 23 July and 2 August 2010, the contribution of BVOC on 23 July (35.4 ppb: 25.6% of daily maximum $O_3$) was much larger than that on 2 August (20.9 ppb: 14.2% of daily maximum $O_3$). To investigate this difference, additional zero-out cases for anthropogenic VOC (AVOC) emissions from Osaka and for VOC emissions on the target days were performed. On 23 July, the urban $O_3$ concentration in Osaka was dominantly increased by the transport from the northwestern region outside Osaka with large contribution of $O_3$ that was produced through BVOC reactions by the day before and was retained over the nocturnal boundary layer. On 2 August, the concentration was dominantly increased by the local photochemical production inside Osaka under weak wind condition with the particularly large contribution of AVOC emitted from Osaka on the day.

• Advances in nano research
• /
• v.10 no.3
• /
• pp.221-234
• /
• 2021

During the previous few years, phenomenon of bioconvection along with the use of nanoparticles showed large number of applications in technological and industrial field. This paper analyzed the bioconvection phenomenon in magnetohydrodynamic boundary layer flow of a Powell-Eyring nanoliquid past a stretchable cylinder with Cattaneo-Christov heat flux. In addition, the impacts of chemical reaction and heat generation/absorption parameter are considered. By the use of appropriate transformation, the governing PDEs (nonlinear) have been transformed and formulated into nonlinear ODEs. The resulting nonlinear ODEs subjected to relevant boundary conditions are solved analytically through homotopy analysis method which is programmed in Mathematica software. Graphical and numerical results versus physical quantities like velocity, temperature, concentration and motile microorganism are investigated under the impact of physical parameters. It is noted that velocity profile enhances as the curvature parameter A and Eyring-Powell fluid parameter M increases but a decline manner for large values of buoyancy ratio parameter Nr and bio-convection Rayleigh number Rb. In the presence of Prandtl number Pr, Eyring-Powell fluid parameter M and heat absorption parameter ��, temperature profile decreases. Nano particle concentration profile increases for increasing values of magnetic parameter Ha and thermophoresis parameter Nt. The motile density profile has revealed a decrement pattern for higher values of bio-convection Lewis number Lb and bio-convection peclet number Pe. This study may find uses in bio-nano coolant systems, advance nanomechanical bio-convection energy conversion equipment's, etc.