Measurements of three chlorofluorocarbons (CFCs): trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) and trichlorotrifluoroethane (CFC-113), along with methyl chloroform (CH 3CCl 3) and carbon tetrachlo...Measurements of three chlorofluorocarbons (CFCs): trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) and trichlorotrifluoroethane (CFC-113), along with methyl chloroform (CH 3CCl 3) and carbon tetrachloride (CCl 4) were made in water samples from Lake Washington, using Electron Capture-Gas Chromatography (EC-GC). The samples were collected in mid-autumn, a period when the lake’s upper layer undergoes rapid cooling. At the time of sampling, a strong vertical temperature gradient was present in the lake, with surface temperatures of ～14℃, and near bottom (50 meters) temperatures of ～8℃. The concentrations of dissolved CFC-12 and CFC-11 increased with depth, as expected from the higher solubilities of these gases at lower temperatures. Atmospheric measurements made at the sampling site at the time of the cruise, showed that CFC-11 and CFC-12 saturations in the near surface samples were 100 % and 106%, respectively. For the deepest sample (52 meters) CFC-11 and CFC-12 saturations were 102 % and 126 %. Because the surface layer of the lake responds to changes in atmospheric CFCs on a time scale of several weeks, the higher than equilibrium concentrations of CFC-12 observed at the time of sampling may reflect earlier episodes of elevated levels of atmospheric CFC-12 in this urban area. High concentrations of dissolved CFCs in runoff or industrial effluent might also lead to elevated CFC levels in the lake. The cold, deep water of Lake Washington is relatively isolated from the effects of surface gas exchange except during winter, and the supersaturations observed in the deep layer may reflect periods of elevated atmospheric CFC-12 levels from the previous winter season. These results were compared to summertime profiles of CFC-11 and CFC-12 made in 1994.展开更多
CO_2 is one of the most important ＂renewable＂ carbon sources.To transform CO_2 to useful organic compounds,we examined the reactivity of two model silicon-based ＂waste＂ materials,disilanes and metallic Si powder,a...CO_2 is one of the most important ＂renewable＂ carbon sources.To transform CO_2 to useful organic compounds,we examined the reactivity of two model silicon-based ＂waste＂ materials,disilanes and metallic Si powder,as reducing agents.In these reactions,fluoride salts were found to be active catalysts：CO_2 was converted to formic acid at atmospheric pressure in the presence of H_2O as a proton source and the silicon-based reducing reagents.Based on in-situ NMR and kinetics analyses,a hydrosilane and penta-coordinate Si species are proposed as the reaction intermediate and active species,respectively.展开更多
文摘Measurements of three chlorofluorocarbons (CFCs): trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) and trichlorotrifluoroethane (CFC-113), along with methyl chloroform (CH 3CCl 3) and carbon tetrachloride (CCl 4) were made in water samples from Lake Washington, using Electron Capture-Gas Chromatography (EC-GC). The samples were collected in mid-autumn, a period when the lake’s upper layer undergoes rapid cooling. At the time of sampling, a strong vertical temperature gradient was present in the lake, with surface temperatures of ～14℃, and near bottom (50 meters) temperatures of ～8℃. The concentrations of dissolved CFC-12 and CFC-11 increased with depth, as expected from the higher solubilities of these gases at lower temperatures. Atmospheric measurements made at the sampling site at the time of the cruise, showed that CFC-11 and CFC-12 saturations in the near surface samples were 100 % and 106%, respectively. For the deepest sample (52 meters) CFC-11 and CFC-12 saturations were 102 % and 126 %. Because the surface layer of the lake responds to changes in atmospheric CFCs on a time scale of several weeks, the higher than equilibrium concentrations of CFC-12 observed at the time of sampling may reflect earlier episodes of elevated levels of atmospheric CFC-12 in this urban area. High concentrations of dissolved CFCs in runoff or industrial effluent might also lead to elevated CFC levels in the lake. The cold, deep water of Lake Washington is relatively isolated from the effects of surface gas exchange except during winter, and the supersaturations observed in the deep layer may reflect periods of elevated atmospheric CFC-12 levels from the previous winter season. These results were compared to summertime profiles of CFC-11 and CFC-12 made in 1994.
基金supported by JSPS KAKENHI(15H04182)JSPS Grant-in-Aid for Scientific Research on Innovative Areas "3D Active-Site Science(26105003)","Precisely Designed Catalysts with Customized Scaffolding(16H01010)"Grant for Challenging Research Award,Tokyo Institute of Technology
文摘CO_2 is one of the most important ＂renewable＂ carbon sources.To transform CO_2 to useful organic compounds,we examined the reactivity of two model silicon-based ＂waste＂ materials,disilanes and metallic Si powder,as reducing agents.In these reactions,fluoride salts were found to be active catalysts：CO_2 was converted to formic acid at atmospheric pressure in the presence of H_2O as a proton source and the silicon-based reducing reagents.Based on in-situ NMR and kinetics analyses,a hydrosilane and penta-coordinate Si species are proposed as the reaction intermediate and active species,respectively.
