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981.
982.
Huimin Wang Nobuko Saigusa Susumu Yamamoto Hiroaki Kondo Takashi Hirano Atsushi Toriyama Yasumi Fujinuma 《Atmospheric environment (Oxford, England : 1994)》2004,38(40):7021-7032
Larch forests are distributed extensively in the east Eurasian continent and are expected to play a significant role in the terrestrial ecosystem carbon cycling process. In view of the fact that studies on carbon exchange for this important biome have been very limited, we have initiated a long-term flux observation in a larch forest ecosystem in Hokkaido in northern Japan since 2000. The net ecosystem CO2 exchange (NEE) showed large seasonal and diurnal variation. Generally, the larch forest ecosystem released CO2 in nighttime and assimilated CO2 in daytime during the growing season from May to October. The ecosystem started to become a net carbon sink in May, reaching a maximum carbon uptake as high as 186 g C m−2 month−1 in June. With the yellowing, senescing and leaf fall, the ecosystem turned into a carbon source in November. During the non-growing season, the larch forest ecosystem became a net source of CO2, releasing an average of 16.7 g C m−2 month−1. Overall, the ecosystem sequestered 141–240 g C m−2 yr−1 in 2001. The NEE was significantly influenced by environmental factors. Respiration of the ecosystem, for example, was exponentially dependent on air temperature, while photosynthesis was related to the incident PAR in a manner consistent with the Michaelis–Menten model. Although the vapor pressure deficit (VPD) was scarcely higher than 15 hPa, the CO2 uptake rate was also depressed when VPD surpassed 10 hPa. 相似文献
983.
984.
Chemical composition of fine particles from incense burning in a large environmental chamber 总被引:3,自引:0,他引:3
This study is aimed to characterize the major chemical compositions of PM2.5 from incense burning in a large environmental chamber. Chemical analyses, including X-ray fluorescence for elemental species, ion chromatography for water soluble inorganic species (chloride, nitrate, sulfate, sodium, potassium, ammonium) and thermal/optical reflectance analysis for carbon species were carried out for combustion of three incense categories (traditional, aromatic and church incense). The average concentrations from incense burning ranged from 139.8 to 4414.7 μg m−3 for organic carbon (OC), and from 22.8 to 74.0 μg m−3 for elemental carbon (EC), respectively. The average OC and EC concentrations in PM2.5 of three incense categories were in the order of church incense>traditional incense>aromatic incense. OC/EC ratios ranged from 7.0 to 39.1 for the traditional incense, with an average of 21.7; from 3.2 to 11.9 for the aromatic incense, with an average of 7.7. The concentrations of Cl−, SO42−, Na+ and K+ were highly variable. On average, the inorganic ion concentration sequence was traditional incense>church incense>aromatic incense. The profiles for elements were dominated by Na, Cl and K. In general, the major components in PM2.5 fraction from incense burning are OC (especially OC2, OC3 and OC4), EC and K. 相似文献
985.
986.
Carbon and hydrogen isotope effects during sorption of organic contaminants on carbonaceous materials 总被引:1,自引:0,他引:1
Stable carbon and hydrogen isotopes can be an efficient means to validate biodegradation of organic contaminants in groundwater since it results in an isotopic fractionation. A prerequisite in applying this method in the field is the proof that other processes decreasing the contaminant concentration are conservative with respect to isotope effects. In this paper we show for carbon isotopes of halogenated hydrocarbon compounds [trichloroethene (TCE), cis-dichloroethene (c-DCE), vinylchloride (VC)] and carbon and hydrogen isotopes of BTEX compounds (benzene, toluene, p-xylene) that no significant fractionation occurs during equilibrium sorption onto activated carbon, lignite coke and lignite. In general, effects were in the range of the reproducibility limit of the analytical instrument (0.5 per thousand for delta13C, and 8 per thousand for delta2H). This observation was made for fractions sorbed of less than 5% to more than 95%. Also for rate-limited sorption of TCE onto activated carbon, no significant fractionation in carbon isotopes could be observed. These findings support the assumption that for these classes of compounds, sorption processes in aquifer systems are conservative with respect to isotope effects. 相似文献
987.
V. Etyemezian M. Tesfaye A. Yimer J.C. Chow D. Mesfin T. Nega G. Nikolich J.G. Watson M. Wondmagegn 《Atmospheric environment (Oxford, England : 1994)》2005,39(40):7849-7860
Twenty-one samples were collected during the dry season (26 January–28 February 2004) at 12 sites in and around Addis Ababa, Ethiopia and analyzed for particulate matter with aerodynamic diameter <10 μm (PM10) mass and composition. Teflon-membrane filters were analyzed for PM10 mass and concentrations of 40 elements. Quartz-fiber filters were analyzed for chloride, sulfate, nitrate, and ammonium ions as well as elemental carbon (EC) and organic carbon (OC) content. Measured 24-h PM10 mass concentrations were <100 and 40 μg m−3 at urban and suburban sites, respectively. PM10 lead concentrations were <0.1 μg m−3 for all samples collected, an important finding because the government of Ethiopia had stopped the distribution of leaded gasoline a few months prior to this study. Mass concentrations reconstructed from chemical composition indicated that 34–66% of the PM10 mass was due to geologically derived material, probably owing to the widespread presence of unpaved roads and road shoulders. At urban sites, EC and OC compounds contributed between 31% and 60% of the measured PM10 while at suburban sites carbon compounds contributed between 24% and 26%. Secondary sulfate aerosols were responsible for <10% of the reconstructed mass in urban areas but as much as 15% in suburban sites, where PM10 mass concentrations were lower. Non-volatile particulate nitrate, a lower limit for atmospheric nitrate, constituted <5% and 7% of PM10 at the urban and suburban sites, respectively. At seven of the 12 sites, real-time PM10 mass, real-time carbon monoxide (CO), and instantaneous ozone (O3) concentrations were measured with portable nephelometers, electrochemical analyzers, and indicator test sticks, respectively. Both PM10 and CO concentrations exhibited daily maxima around 7:00 and secondary peaks in the late afternoon and evening, suggesting that those pollutants were emitted during periods associated with motor-vehicle traffic, food preparation, and heating of homes. The morning concentration maxima were likely accentuated by stable atmospheric conditions associated with overnight surface temperature inversions. Ozone concentrations were measured near mid-day on filter sample collection days and were in all cases <45 parts per billion. 相似文献
988.
Angela Dibenedetto Rosa Lo Noce Carlo Pastore Michele Aresta Carlo Fragale 《Environmental Chemistry Letters》2006,3(4):145-148
A new biotechnological synthetic approach to 4-hydroxybenzoic acid is reported. Thauera aromatica cells produce the phenylphosphate carboxylase enzyme that selectively carboxylates phenylphosphate in the para position, without any formation of the ortho isomer. Here we show that the enzyme also works in supercritical carbon dioxide, opening a new technological solution to the recovery of the products that is a key problem when aqueous media are used. The enzyme shows an activity comparable with that shown under CO2 pressure in aqueous media and does not require the presence of NaHCO3. 相似文献
989.
Christopher P. Williams 《Environmental Chemistry Letters》2007,5(4):197-202
Radiocarbon from nuclear fallout is a known health risk. However, corresponding risks from natural background radiocarbon
incorporated directly into human genetic material have not been fully appreciated. Here we show that the average person will
experience between 3.4 × 1010 and 3.4 × 1011 lifetime chromosomal damage events from natural background radiocarbon incorporated into DNA and histones, potentially leading
to cancer, birth defects, or accelerated aging. This human genetic damage can be significantly reduced using low radiocarbon
foods produced by growing plants in CO2 recycled from ordinary industrial greenhouse gas fossil fuel emissions, providing additional incentive for the carbon sequestration. 相似文献
990.
Anna Szynkiewicz Mariusz Orion Jędrysek Marta Kurasiewicz 《Environmental Chemistry Letters》2006,4(1):29-35
Here we demonstrate that precipitation of dissolved inorganic carbon (DIC) to at pH 10.26, 11.38 and 12.11 does not cause
measurable carbon isotope fractionation. However, NaOH solution prepared under standard laboratory procedure and used to increase
pH value for precipitation of BaCO3 can be contaminated by atmospheric CO2. In our experiment, δ13C value in the contaminant DIC was −24.30‰, which resulted in decrease in the δ13C(DIC) value by 0.03, 0.07 and 0.22 at pH 10.26, 11.38 and 12.11, respectively. 相似文献