• 대기
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• 제33권5호
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• pp.549-560
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• 2023

This study evaluates three distinct observation methods, CRDS, OA-ICOS, and OF-CEAS, in greenhouse gas monitoring equipment for atmospheric CO₂ and CH₄ concentrations. The assessment encompasses fundamental performance, high-concentration measurement accuracy, calibration methods, and the impact of atmospheric humidity on measurement accuracy. Results indicate that within a range of approximately 500 ppm, all three devices demonstrate high accuracy and linearity. However, beyond 1000 ppm, CO₂ accuracy sharply declines (84%), emphasizing the need for caution when interpreting high-concentration CO₂ data. An analysis of calibration methods reveals that both CO₂ and CH₄ measurements achieve high accuracy and linearity through 1-point calibration, suggesting that multi-point calibration is not imperative for precision. In dynamic atmospheric conditions with significant CO₂ and CH₄ concentration variations, a 1-point calibration suffices for reliable data (99% accuracy). The evaluation of humidity impact demonstrates that humidity removal devices significantly reduce air moisture levels, yet this has a negligible effect on dry CO₂ concentrations (less than 0.5% relative error). All three observation method instruments, which have integrated humidity correction to calculate dry CO₂ concentrations, exhibit minor sensitivity to humidity removal devices, implying that additional removal devices may not be essential. Consequently, this study offers valuable insights for comparing data from different measurement devices and provides crucial information to consider in the operation of monitoring sites.

• 한국연소학회지
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• 제5권1호
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• pp.7-18
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• 2000

Numerical simulations of counterflow non-premixed $CH_4/C_2HCl_3/Air$ flames added 8%(by volume) C2HCl3 on the fuel side are conducted at atmospheric pressure using a detailed chemical reaction mechanism in order to understand the effect of strain rates. A detailed sensitivity analysis is also performed in order to assess the relative influence of each reaction on the flame established at a strain rate of 200s-1. The structure of flames (i.e., temperature, velocity, and concentration of species) established at both a strain rate of 150s-1 and 300s-1 are investigated. As the strain rate increases, the "flame zone" is restricted to a narrower range and the position of maximum temperature is shifted to the fuel side. The concentrations of major species, H2O, CO, H2, HCl, Cl2, and Cl are decreased with increased strain rate. The reaction involving chlorine, CH4 + Cl $\rightarrow$ CH3 + HCl, instead of the reaction, CH4 + H $\rightarrow$ CH3 + H2 influences the consumption of methane. C2HCl3 + OH $\rightarrow$ CHCl2 + CHOCl and HCl + OH $\rightarrow$ H2O + Cl, are major reactions, through which OH radicals are consumed.

• Fisheries and Aquatic Sciences
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• 제7권4호
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• pp.204-214
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• 2004

The effect of wind. stresses on the flow and water quality has been examined, particularly focused on the environment of oyster farms in Gamak Bay, by a two dimensional numerical model. In autumn (wind: $45.0^{\circ}$, 4.3 m/s), the overall flow turned out to be stronger than any other seasons and in addition, a pair of anticlockwise and clockwise vortices has been created at the northwest of the bay. Consequently, the wind in autumn seemed efficient not only for growing oyster but also for reducing the water pollution as the flow becomes much more active. In summer an anoxic condition appeared around the northwest of the bay where the flow is stagnant. According to a field survey, the majority of oyster farms tended to be densely distributed around the areas where DO concentration is high. Furthermore, oyster farms with a high production (over 1,300 kg per hanging string of 100 m) were distributed along with approximately 4 of Ch-a concentration. This suggests that oyster production is closely related to the concentration of DO or Ch-a.

• Journal of Preventive Medicine and Public Health
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• 제25권1호
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• pp.13-25
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• 1992

This study was conducted to investigate the mechanism of protective effect by sodium selenite in methylmercuric chloride neurotoxicity, increasing intracellular $Ca^{2+}$concentration of the neuron. Methylmercuric chloride of 3mg/kg of body weight was administered simultaneously with sodium selenite of 5mg/kg and pretreatment of sodium selenite via intraperitoneal injection to rats. Also, effect of methylmercuric chloride($25{\mu}M,\;50{\mu}M,\;100{\mu}M$) and sodium selenite($200{\mu}M$) on free intrasynaptosomal $Ca^{2+}$ concentration were studied using the fluorescent $Ca^{2+}$ indicator fura -2 in vitro. After the treatment, at 6, 24, and 48 hours later, mercury in the cerebral cortex, liver and kidney tissues, succlnic dehydrogenase activities, adenosin-5'-triphosphate concentration, acetylcholinesterase activities, and intracellular $Ca^{2+}$ concentration in the cerebral cortex were determined in vivo. Cerebral synaptosomes of rats were incubated with methylmercuric chloride and sodium selenite in Hepes buffer for 10 minutes and free intrasynaptosomal $Ca^{2+}$ concentration were measured with fura-2 in vitro. The results were summarized as follows ; 1. The combined administration of $CH_3HgCl$ and $Na_2SeO_3$ and pretreatment of $Na_2SeO_3$ according to time significantly more increased in the cerebral cortex and decreased in the liver, kidney mercury concentrations compared to the administration of $CH_3HgCl$ only. 2. The combined administration of $CH_3HgCl$ and $Na_2SeO_3$ and pretreatment of $Na_2SeO_3$ increased more succinic dehydrogenase and acetylcholinesterase activities compared to the administration of $CH_3HgCl$ only. Particularly pretreatment of $Na_2SeO_3$ significantly more compared to the administration of $CH_3HgCl$ only. The concentration of adenosine-5'-triphosphate in $Na_2SeO_3$ treatment groups revealed a favourable effect compared to the administration of $CH_3HgCl$ only. 3. Intracellular $Ca^{2+}$ concentration in administration of $CH_3HgCl$ only was increased significantly more than control group in all test hours but was increased significantly more at 48 hours only after treatment in combined administration of $CH_3HgCl$ and $Na_2SeO_3$ and pretreatment of $Na_2SeO_3$ according to time interval more decreased significantly intracellular $Ca^{2+}$ concentration compared to the administration of $CH_3HgCl$ only. 4. Free intrasynaptosomal $Ca^{2+}$ concentration in the combined administration of $CH_3HgCl$ and $Na_2SeO_3$ was decreased ($24%{\sim}40%$) significantly more than the administration of $CH_3HgCl$ only. From the above results, the specific dosage of $Na_2SeO_3$ decreased increment of intracellular $Ca^{2+}$ concentration induced by administration of $CH_3HgCl$. These findings suggest the protective mechanism of $Na_2SeO_3$ on the neurotoxicity of $CH_3HgCl$.

• 대한기계학회논문집B
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• 제26권5호
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• pp.742-749
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• 2002

Numerical Study with detailed chemistry has been conducted to investigate the flame structure and NOx formation characteristics in oxygen -enhanced(CH$_4$/O$_2$-$N_2$) and oxygen-enhanced-EGR(CH$_4$/O$_2$-$CO_2$) counter diffusion flame with various strain rates. A small amount of $N_2$is included in oxygen-enhanced-EGR combustion, in order to consider the inevitable $N_2$contamination by $O_2$production process or air infiltration. The results are as follows : In CH$_4$/O$_2$-$CO_2$flame it is very important to adopt a radiation effect precisely because the effect of radiation changes flame structure significantly. In CH$_4$/O$_2$-$N_2$flame special strategy to minimize NO emission is needed because it is very sensitive to a small amount of $N_2$. Special attention is needed on CO emission by flame quenching, because of increased CO concentration. Spatial NO production rate of oxygen-enhanced combustion is different from that of air and oxygen-enhanced-EGR combustion in that thermal mechanism plays a role of destruction as well as production. In case CH$_4$/O$_2$-$CO_2$flame contains more than 40% $CO_2$it is possible to maintain the same EINO as that of CH$_4$/Air flame with accomplishing higher temperature than that of CH$_4$/Air flame. EINO decreases with increasing strain rate, and those effects are augmented in CH$_4$/O$_2$flame.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.185-190
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• 2001

Numerical Study with detailed chemistry has been conducted to investigate the flame structure and NOx formation characteristics in oxygen-enhanced$(CH_4/O_2-N_2)$ and oxygen-enhanced-EGR$(CH_4/O_2-CO_2)$ counter diffusion flame with various strain rates. A small amount of $N_2$ is included in oxygen-enhanced-EGR combustion, in order to consider the inevitable $N_2$ contamination by $O_2$ production process or air infiltration. The results are as follows : In $CH_4/O_2-CO_2$ flame it is very important to adopt a radiation effect precisely because the effect of radiation changes flame structure significantly. In $CH_4/O_2-N_2$ flame special strategy to minimize NO emission is needed because it is very sensitive to a small amount of $N_2$. Special attention is needed on CO emission by flame quenching, because of increased CO concentration. Spatial NO production rate of oxygen-enhanced combustion is different from that of air and oxygen-enhanced-EGR combustion in that thermal mechanism plays a role of destruction as well as production. In case $CH_4/O_2-CO_2$ flame contains more than 40% $CO_2$ it is possible to maintain the same EINO as that of $CH_4/Air$ flame with accomplishing higher temperature than that of $CH_4/Air$ flame. EINO decreases with increasing strain rate, and those effects are augmented in $CH_4/O_2$ flame. Complementary study is needed with extending the range of strain rate variation.

• Bulletin of the Korean Chemical Society
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• 제17권10호
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• pp.939-943
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• 1996

Reactions that proceed within mixed acetylene-methanol and ethylene-methanol cluster ions were studied using an electron-impact time-of-flight mass spectrometer. When acetylene and methanol seeded in helium are expanded and ionized by electron impact, the ion abundance ratio, [CH3OH+]/[CH2OH+] shows a propensity to increase as the acetylene/methanol mixing ratio increases, indicating that the initially ionized acetylene ion transfers its charge to adjacent methanol molecules within the clusters. Investigations on the relative cluster ion intensity distributions of [CH3OH2+]/[CH3OH+] and [(CH3OH)2H+]/[CH3OH·CH2OH+] under various experimental conditions suggest that hydrogen-atom abstraction reaction of acetylene molecule with CH3OH ion is responsible for the effective formation of CH2OH ion. In ethylene/methanol clusters, the intensity ratio of [CH3OH2]/[CH3OH] increases linearly as the relative concentration of methanol decreases. The prominent ion intensities of (CH3OH)mH over (CH3OH)m-1CH2OH ions (m=1, 2, and 3) at all mixing ratios are also interpreted as a consequence of hydrogen atom transfer reaction between C2H4 and CH3OH to produce the protonated methanol cluster ions.

• 한국진공학회지
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• 제2권3호
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• pp.346-354
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• 1993

고주파플라즈마 CVD법으로 CH4와 H2의 혼합가스로부터 실리콘과 석영기판 위에 다이아몬드 입자와 박막을 성장시켰다. 기판과 기판지지대 사이에 금속판을 삽입함으로써 기판의 온도와 성장된 박막의 두께를 비교적 균일하게 할 수 있었다. 방전전력이 같은 경우 성장된 박막의 형태는 반응관 압력을 증가시킴에 따라 자형면을 가진 입자로부터 미립자 도는 구성의 입자로 변화되었다. $H_2와{\;}CH_4의$ 혼합가스로부터 Si기판 위에 다이아몬드 박막을 성장시키는 경우, CH4 농도가 0.5vol% 이하가 되어야만 양질의 다이아몬드 박막을 성장시킬 수 있었다. 성장된 다이아몬드 박막은 SEM, XRD 및 Raman 분광기를 사용하여 평가하였다.

• 한국환경농학회지
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• 제33권4호
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• pp.306-313
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• 2014

BACKGROUND: Forest soils contain microbes capable of consuming atmospheric methane ($CH_4$), an amount matching the annual increase in $CH_4$ concentration in the atmosphere. However, the effect of plant residue production by different forest structure on $CH_4$ oxidation is not studied in Korea. The objective of this study was to evaluate the effect of Korean alpine soils having different forestation structure on $CH_4$ uptake rates. METHODS AND RESULTS: the $CH_4$ flux was measured at three sites dominated with pine, chestnut and oak trees in southern Korea. The $CH_4$ uptake potentials were evaluated by a closed chamber method for a year. The $CH_4$ uptake rate was the highest in the pine tree soil ($1.05mg/m^2/day$) and then followed by oak ($0.930mg/m^2/day$) and chestnut trees ($0.497mg/m^2/day$). The $CH_4$ uptake rates were highly correlated to soil organic matter and moisture contents, and total microbial and methanotrophs activities. Different with the general concent, there was no any correlation between $CH_4$ oxidation rates, and soil temperature and labile carbon concentrations, irrespective with tree species. CONCLUSION: Conclusively, the methane oxidation rate was correlated in positive manner with organic matter, abundance of methanotrophs. Methane oxidation was different among tree species. This results could be used to estimate methane oxidation rate in forest of Korea after complementing information about statistical data and methane oxidation of other site.

• Journal of Microbiology and Biotechnology
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• 제25권4호
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• pp.423-430
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• 2015

Aerobic CH₄ oxidation is an important CH₄ sink in landfills. To investigate the distribution and community diversity of methanotrophs and link with soil characteristics and operational parameters (e.g., concentrations of O₂, CH₄), cover soil samples were collected at different locations and depths from the Mengzi semi-aerobic landfill (SAL) in Yunnan Province of southern China. Specific PCR followed by denaturing gradient gel electrophoresis and realtime PCR were used to examine methanotrophs in the landfill cover soils. The results showed that different locations did harbor distinct methanotroph communities. Methanotrophs were more abundant in areas near the venting pipes because of the higher O₂ concentrations. The depth of 20-25 cm, where the ratio of the CH₄ to O₂ was within the range from 1.3 to 8.6, was more conducive to the growth of CH₄-oxidizing bacteria. Type II methanotrophs dominated in all samples compared with Type I methanotrophs, as evidenced by the high ratio of Type II to Type I methanotrophic copy numbers (from 1.76 to 11.60). The total copy numbers of methanotrophs detected were similar to other ecosystems, although the CH₄ concentration was much higher in SAL cover soil. Methylobacter and Methylocystis were the most abundant Type I and Type II methanotrophs genera, respectively, in the Mengzi SAL. The results suggested that SALs could provide a special environment with both high concentrations of CH₄ and O₂ for methanotrophs, especially around the vertical venting pipes.