• 한국환경과학회지
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• 제32권9호
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• pp.613-626
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• 2023

This study investigates the impact of increased adoption of eco-friendly vehicles on ozone (O₃) concentrations in South Korea, utilizing the community multiscale air quality (CMAQ) model. In the summer of 2017 (June-August), we conducted two experiments: a BASE experiment, representing baseline emissions, and an R_30 experiment, involving a 30% emission reduction due to eco-friendly vehicles. The contrast between these experiments reveals that, while most air pollutants decreased with reduced vehicle emissions, O₃ concentrations surprisingly increased (up to 2.1 parts per billion) across South Korea. A further examination of O₃ concentration changes was conducted by analyzing daytime and nighttime variations as well as wind direction. During the daytime, O₃ concentrations notably rose near metropolitan areas due to reduced O₃ titration (O₃ + NO → O₂ + NO₂) resulting from emission reductions. At nighttime, O₃ concentrations exhibited a greater increase, attributed to the transport of daytime-generated O₃ to rural regions. Notably, the impact of reduced emissions in metropolitan areas on O₃ concentrations in downwind areas varied depending on the prevailing wind direction. These findings highlight that the promotion of eco-friendly vehicles, though effective in lowering certain air pollutants, might not directly influence O₃ concentrations. This study underscores the need to comprehensively understand the complicated chemistry of O₃ to develop effective strategies for air quality management.

• 한국전기전자재료학회논문지
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• 제32권1호
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• pp.78-85
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• 2019

The effect of various lithium sources such as LiCl, LiOH, and Li-metal on the microstructure and electrochemical properties of granulated $SiO_x$ powders were investigated. Various lithium sources were metallurgically added for a passive pre-lithiation of $SiO_x$ to improve its low initial coulombic efficiency. In spite of using the same amount of Li in various sources, as well as the same process conditions, different lithium silicates were obtained. Moreover, irreversible phases were formed without reduction of $SiO_x$, which might be from additional oxygen incorporation during the process. Accordingly, there were no noticeable electrochemical enhancements. Nevertheless, the $Li_4SiO_4$ phase changes the initial electrochemical reaction, and consequently the relationship between the microstructure and electrochemical properties of metallurgically pre-lithiated $SiO_x$ could provide a guideline for the optimization of the performance of lithium ion batteries.

• 한국자동차공학회논문집
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• 제16권3호
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• pp.66-72
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• 2008

Fuel reforming technology for the fuel cell vehicles could be adopted to internal combustion engine for the reduction of engine out emissions. Since syngas which is reformed from fossil fuel has hydrogen as a major component, it has abilities to enhance the combustion characteristics with wide flammability and high speed flame propagation. In this paper, syngas was feed to 2.0 liter gasoline engine during the cold start and early state of idle condition. Not only cold start HC emission but also $NO_x$ emission could be dramatically reduced due to the fact that syngas has no HC and has nitrogen up to 50% as components. Exhaust gas temperature was lower than that of gasoline feeding condition. Delayed ignition timing, however, resulted in increased exhaust gas temperature approximated to gasoline condition. It is supposed that the usage of syngas in the gasoline internal combustion engine is an effective solution to meet the future strict emission regulations by the reduction of cold start THC and $NO_x$ emissions.

• 공업화학
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• 제17권4호
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• pp.409-413
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• 2006

$150{\sim}200^{\circ}C$의 저온조건에 적용하기 위한 탈질공정으로서 저온 플라즈마 및 암모니아 SCR 공정을 복합시킨 탈질공정에 대한 실험적인 연구가 수행되었다. 실험결과 저온조건에서 일반적인 SCR 반응에 비해 매우 빠른 반응속도를 갖는 fast SCR 반응의 가능성을 확인할 수 있었으며, 효과적인 fast SCR 반응을 위해서는 SCR 반응기에 투입되는 $NO_{2}/NO_{x}$의 비가 0.3~0.5 범위에 있음을 알 수 있었다. 본 연구에서는 저온운전에 따른 암모늄염의 발생문제, 배기가스에 포함되어 있는 탄화수소가 공정에 미치는 영향, 유사한 공정과의 운전전력 비교 등 해당기술을 활용하기 위해 기본적으로 필요한 자료를 제공하고 있다.

• Communications for Statistical Applications and Methods
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• 제24권3호
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• pp.303-315
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• 2017

Yoo (2015, Statistics and Probability Letters, 99, 109-113) derives theoretical results in an optimal sufficient dimension reduction with singular inner-product matrix. The results are promising, but Yoo (2015) only presents one simulation study. So, an evaluation of its practical usefulness is necessary based on numerical studies. This paper studies the asymptotic behaviors of Yoo (2015) through various simulation models and presents a real data example that focuses on ordinary least squares. Intensive numerical studies show that the $x^2$ test by Yoo (2015) outperforms the existing optimal sufficient dimension reduction method. The basis estimation by the former can be theoretically sub-optimal; however, there are no notable differences from that by the latter. This investigation confirms the practical usefulness of Yoo (2015).

• 한국표면공학회지
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• 제56권5호
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• pp.320-327
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• 2023

In this study, the nickel hydroxide (Ni(OH)₂) electrode for supercapacitor was prepared via hydrothermal method. Based on the nickel (Ni) foam, the electrode does not require any additional binder material or post-processing. Nickel nitrate (Ni(NO₃)₂) and hexamethylenetetramine (C₆H₁₂N₄) were used for synthesis, and the synthesis condition was 12 hours at 80 ℃. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were used to analyze the structural characteristics of the electrode, and it shown that the nickel hydroxide was successfully prepared after only the one-step hydrothermal synthesis. The electrochemical properties were analyzed through the half-cell test. The prepared electrode shown a pair of oxidation/reduction peaks, indicating that the driving method included the redox reaction on the electrode surface. After the charge/discharge test, the specific capacitance was calculated as the value of 438 F/g at 3 A/g.

• 해양환경안전학회지
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• 제27권7호
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• pp.1074-1081
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• 2021

아산화질소(N₂O, Nitrous Oxide)는 6대 온실가스 중 하나로 대기 중에서 적외선을 흡수하여 온실효과를 유발하는 것으로 알려져 있다. 특히 지구온난화지수(GWP)는 CO₂에 비해 310배 높아 국내뿐만 아니라 전 세계적으로 이슈화되고 있으며, 그에 따른 강력한 환경 규제 강화법들이 발의되고 있다. N₂O 저감 기술에는 물리적인 방식에 따라 농축회수, 촉매분해, 그리고 열분해로 구분할 수 있는데, 본 연구에서는 그 중 가장 효과적인 열분해 처리방식에 대해 논의하고자 일반적인 연소 조건 내 고온 열분해 방식을 이용하여 비용 저감과 함께 질소산화물을 저감시키는 온도 조건 및 반응 시간에 대한 정보를 제공하고자 한다. 열분해 조건으로 선정된 고온 영역은 1073 K부터 1373 K까지 100 K 간격을 두고 계산을 수행하였다. 1073 K과 1173 K의 온도조건에 경우, N₂O 저감율과 일산화질소 농도가 체류시간에 따라 비례관계를 이루는 것이 관측되었으며, 1273 K에 경우, 체류시간이 증가함에 따라 발생되는 역반응으로 인해 N₂O 저감율이 감소되는 것이 관측되었다. 특히 1373 K에 경우, 모든 체류시간에 대해 정반응과 역반응이 화학 평형상태에 도달하여 N₂O 저감에 대한 반응진행율이 오히려 감소하는 것으로 확인되었다.

• 한국분무공학회지
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• 제25권1호
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• pp.21-26
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• 2020

The objective of this work is to numerically reveal the effect of equivalence ratio change on the simultaneous reduction of NO_X and soot emissions from the simulated-EGR compression ignition engine containing CO₂. An experiment was conducted by using a single-cylinder common-rail injection system engine, an intake control system, and exhaust emissions analyzers. The numerical analysis results were validated under the same experimental conditions. To investigate the effect of equivalence ratio by simulated-EGR containing CO₂, the O₂, N₂, and CO₂ mole fraction were changed in the initial air conditions to the cylinder. The results were analyzed in terms of peak cylinder pressure, indicated mean effective pressure, indicated specific nitrogen oxide, and indicated specific soot. It was revealed that ignition delay characteristics and heat release rate (ROHR) characteristics were not significantly different according to the equivalence ratio. However, as the equivalence ratio increased from 0.68 to 0.83, the maximum combustion pressure and IMEP decreased by about 6.5% and 9.4%, respectively. In the case of ISFC, as is well known, the trend is opposite of IMEP. In the case of ISNO, as the equivalence ratio increased, less NO was generated, and as the equivalence ratio increased by 0.05, the ISSoot value of about 10% increased.

• 한국표면공학회지
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• 제24권1호
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• pp.1.2-1.2
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• 1991

The formation of managanese ferrite has been performed to investigate some properties according to the variation of compositions, pH, current density by electrolysis. It has been found that the amount of oxidized weight of anode were increased with increasing current density. The amount of oxidized weight of anode were most in pH10. As the result of X-ray diffraction Mn Fe2O4 crystal composition in pH13. When the particles of Mnx Fe3-x O4 were heated at 30$0^{\circ}C$, it has been shown typical MnFe2O4(JCPDS Card No. 10-319) in X-1 composition. As the result of SEM observation, the size of MnFe2O4 particles were about 0.1$\mu\textrm{m}$, the shape of particles were spherical type. According to the above mentioned experimental condition, 0.1-0.5$\mu\textrm{m}$ sub-micron particles of manganese ferrite were formed from the wasted manganese dry cell, through washing longrightarrow reduction longrightarrow electrloysis.

• 한국대기환경학회지
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• 제34권5호
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• pp.708-726
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• 2018

In this study, we examined the contribution of nitrogen oxides and volatile organic compounds emitted from China and Japan to ozone concentrations over Gwangyang-bay, South Korea. We used a chemical transport model, Community Multi-scale Air Quality model, and its instrumented sensitivity tool, High-order Decoupled Direct Method. Intercontinental Chemical Transport Experiment-Phase B 2006 for East Asia and Clean Air Policy Support System 2007 emissions inventories for South Korea were used for the ozone simulation. During the study period, May 2007, the modeled maximum daily 8-hr average ozone concentration among seven air quality monitors in Gwangyang-bay was 68.8 ppb. The contribution of $NO_x$ emissions from China was 19.5 ppb (28%). The highest modeled ozone concentrations and Chinese contributions appeared when air parcels were originated from Shanghai area. The observed 8-hr average ozone concentrations in Gwangyang Bay exceeded the national ambient air quality standard (60 ppb) 203 times by daytime and 56 times by nighttime during the period. It was noticed that many exeedances happened when contribution of Chinese emissions to ozone concentrations over the area increased. Sensitivity analysis shows that a reduction in Chinese $NO_x$ and VOC emissions by 15% could lessen the total exceedance hours by 24%. This result indicates that high ozone concentrations over Gwangyang-bay are strongly enhanced by Chinese emissions.