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Prediction of CO leakage into biosphere is very important for risk assessment in geological carbon storage projects. Underground CO can be transported into biosphere through short term leakage due to fractures of wellbores or cap rocks, which has been extensively investigated, and long term leakage due to diffusion, which has few relevant studies. This paper presents a diffusive model for CO gradual leakage into biosphere during a long period after CO injection. First, the paper describes a general diffusive model with long term secondary trapping effects for CO fluxes from underground into biosphere. Secondly, a simplified one-dimensional model is presented and solved for the CO concentrations in groundwater. The results show that the groundwater CO concentration will reach the maximum value at about 50th year after CO injection and then slowly decrease due to secondary trapping effects. Moreover, the partition coefficient is the dominant parameter for predicting the groundwater CO concentration while the convective mass transfer coefficient plays an insignificant role. [ABSTRACT FROM AUTHOR]

In this paper, polyethyleneimine (PEI) and reduced graphene oxide (RGO) were selected as sensing materials for carbon dioxide detection. Two kinds of sensors with different sensitive film structures, i.e., RGO-PEI composite film and RGO-PEI bi-layer film were fabricated by airbrushing the sensitive films on interdigitated electrodes. Response performances of both sensors at room temperature were investigated. Results showed that sensors with bi-layer film exhibited smaller baseline drift and more stable sensing characteristics than the counterparts with composite film. Furthermore, bi-layer film sensors with different quantity of PEI solution deposited were studied. Performances of long-time stability, repeatability, low concentration of detection for carbon dioxide, and measurements of response time and recovery time were investigated. It was found that appropriate weight ratio of RGO and PEI was critical for sensing response. In addition, the sensor with bi-layer film exhibited a better repeatability but had longer response time and recovery time than RGO single-layer sensor, and both of them could detect as low as 20 parts per million carbon dioxide gas. Sensing responses of the prepared sensors to carbon dioxide under dry air or nitrogen were compared. The relevant sensing mechanisms were studied as well. [ABSTRACT FROM AUTHOR]

Injection of fuel containing CO2 has potential to reduce NOx and soot emissions in a diesel engine. This paper presents an experimental study on the spray characteristics of fuel containing CO2 as measured by phase doppler anemometry (PDA). Experiments were performed under atmospheric conditions on diesel hole-type nozzles at constant injection pressure. Effects of CO2 concentration in diesel fuel on the spray pattern, droplet size and velocity were measured. Experimental results show that fuel atomization will improve greatly when the concentration of dissolved CO2 in the fuel exceeds the critical value. The axial and radial velocity of the fuel spray containing CO2 is larger than that of conventional diesel fuel spray near the nozzle exit due to flash boiling phenomena. Downstream of the spray, the radial velocity and droplet size of fuel containing CO2 is much more uniform and smaller than that of pure diesel spray. It is attributed to the greatly enhanced liquid-gas mixing resulting from flash separation of CO2 from the liquid. New insight into the atomization of the fuel containing CO2 was obtained and a possible mechanism to explain the phenomena was proposed. The method may be developed into a new technique for controlling diesel combustion and exhaust emissions. [ABSTRACT FROM AUTHOR]

Observations of atmospheric carbon dioxide (CO) from satellites offer new data sources to understand global carbon cycling. The correlation structure of satellite-observed CO can be analyzed and modeled by geostatistical methods, and CO values at unsampled locations can be predicted with a correlation model. Conventional geostatistical analysis only investigates the spatial correlation of CO, and does not consider temporal variation in the satellite-observed CO data. In this paper, a spatiotemporal geostatistical method that incorporates temporal variability is implemented and assessed for analyzing the spatiotemporal correlation structure and prediction of monthly CO in China. The spatiotemporal correlation is estimated and modeled by a product-sum variogram model with a global nugget component. The variogram result indicates a significant degree of temporal correlation within satellite-observed CO data sets in China. Prediction of monthly CO using the spatiotemporal variogram model and space-time kriging procedure is implemented. The prediction is compared with a spatial-only geostatistical prediction approach using a cross-validation technique. The spatiotemporal approach gives better results, with higher correlation coefficient ( r), and less mean absolute prediction error and root mean square error. Moreover, the monthly mapping result generated from the spatiotemporal approach has less prediction uncertainty and more detailed spatial variation of CO than those from the spatial-only approach. [ABSTRACT FROM AUTHOR]

Carbon isotopic compositions of soil CO2 in rainy season (July) from two natural soil profiles (DHLS & DHS) in the monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir (DBR), South China, are presented. Turnover and origins of soil CO2 are preliminarily discussed in this paper. Results show that the content of soil CO2 varies between 6120 and 18718 ppmv, 13 and increases with increasing depth until 75 cm, and then it declines. In DHLS, soil CO2 δ 13C ranges from -24.71‰ to -24.03‰, 2 showing a significant inverse correlation (R =0.91) with the soil CO2 content in the same layer. According to a model related to soil CO2 δ 13C, the soil CO2 is mainly derived from the root respiration (>80%) in DHLS. While in DHS, where soil CO2 δ 13C ranges from -25.19‰ to -22.82‰, soil CO2 is primarily originated from the decomposition of organic matter (51%--94%), excluding the surface layer (20 cm, 90%). Radiocarbon data suggest that the carbon in soil CO2 is modern carbon in both DHLS xand DHS. Differences in 14C ages between the "oldest" and "youngest" soil CO2 in DHLS and DHS are 8 months and 14 months, respectively, indicating that soil CO2 in DHLS has a faster turnover rate than that in DHS. The Δ 14C values of soil CO2, which range between 100.0‰ and 107.2‰ and between 102.5‰ and 112.1‰ in DHLS and DHS, respectively, are obviously higher than those of current atmospheric CO2 and SOC in the same layer, suggesting that soil CO2 is likely an important reservoir for Bomb- 14C in the atmosphere. [ABSTRACT FROM AUTHOR]

Relationships on interannual and interdecadal timescales among global mean air temperature, CO2 concentrations and fossil-fuel carbon emissions in four major developed countries (the United States, the United Kingdom, France, and Germany) were analyzed. On an interannual timescale, the United States fossil-fuel carbon emissions tend to increase during cold winters and decrease during warm winters, which is opposite to the situation in summer. On an interdecadal timescale, cold (warm) periods both in the United States and globally agree with high (low) periods of fossil-fuel carbon emissions, with the temperature variability leading by 5-7 years. The leading correlation on the interdecadal timescale and the asymmetry in seasonal correlation on the interannual timescale indicate that temperature variability is a possible cause of changes in fossil-fuel carbon emissions. [ABSTRACT FROM AUTHOR]

Under an Ensemble Kalman Filter (EnKF) framework, Regional Atmospheric Modeling System and Models-3 Community Multi-scale Air Quality (RAMS-CMAQ) modeling system is developed to be a CO data assimilation system EnKF-CMAQ, and the EnKF-CMAQ system is then applied to East Asia for validation with real continuous surface CO concentration observations available in the study domain instead of using an observation simulation system experiment. Experiments with an experimental period of January 23 to February 7, 2007 are conducted, and the experimental results of the EnKF-CMAQ system and the RAMS-CMAQ model are compared against continuous surface CO observations from assimilation sites and independent reference sites. Distributions of daily mean CO concentration increments show that the EnKF-CMAQ system confines the update of daily mean CO within areas nearby and downwind of the assimilation sites. Both the CO concentration ensemble spreads and background error covariances show flow-dependent patterns. The results indicate the crucial role of wind transport in the CO data assimilation, which agrees with the previous studies. The average bias and the average root-mean-square error (RMSE) of daily mean CO concentration at the assimilation sites are reduced by 1.00 and 1.83 ppm, respectively, and those at the reference sites are reduced by 0.24 and 0.22 ppm, respectively. The results demonstrate the EnKF-CMAQ system is capable of assimilating the continuous surface CO concentration observations to improve the simulation accuracy of the atmospheric CO synoptic variation. Since growing CO observations over East Asia are being available nowadays, this work is our first step to generate consistent spatial and temporal atmospheric CO concentration fields over East Asia, particularly over China, using both in situ and satellite observations. [ABSTRACT FROM AUTHOR]

Soil respiration (Soil R) is one of the largest CO fluxes from terrestrial ecosystems to the atmosphere. The largely seasonal and daily patterns of Soil R in semiarid grassland ecosystems indicate that measurement time and frequency would have significant influences on the assessment of seasonal soil carbon release. Based on a three-year continuous measurement of Soil R in a semiarid grassland, we found that the Soil R value measured at around 10:00 o'clock local time was the closest to its daily mean, while the value at 14:00 o'clock was found to be the highest daily rate. A measurement frequency higher than every 10 days was necessary for estimating the seasonal Soil R and its temperature sensitivity ( Q) reasonably. Our study would be useful as guidelines for manual Soil R measurements and model data selection in semiarid temperate grasslands. [ABSTRACT FROM AUTHOR]

Two-dimensional metal oxide nanostructures, such as nanoplates, nanowalls, and nanosheets, have received further attentions in recent years, due to their outstanding properties resulted from the small thickness and quantum size effects. In this work, lanthanum oxide nanosheets with the thickness of 56 nm had been successfully prepared by an originally simple method of carbon dioxide carbonation; the preparation process was green without using surfactants and detergent. The X-ray diffraction, transmission electron microscopy, and scanning electron microscopy were used to characterize the products. Thermogravimetric-differential thermal analysis and FT-IR were introduced to prove that the lanthanum oxide precursor with lamellar morphology was La(CO)·3HO. The carbon dioxide carbonation method would provide significant benefits containing mild reaction conditions, high efficiency, low cost, and easy to realize large-scale production. [ABSTRACT FROM AUTHOR]

Climate change is expected to cause the alteration of litter production in forests, which may result in substantial changes in soil CO efflux (FCO) process as litter represents a major pathway of carbon from vegetation to the soils. In this study, we conducted an aboveground litter manipulation experiment to examine the influence of litter addition and exclusion on soil FCO in Camphor tree, Masson pine, and mixed Camphor tree and Masson pine forests in central south China. Litter input manipulation included three treatments: non-litter input (litter exclusion), double litter input (litter addition), and natural litter input (control). On average, litter exclusion significantly reduced soil FCO rate by approximately 39%, 24% and 22% in Camphor tree forests, the Mixed forests, and Masson pine forests, respectively. On a yearly basis, double litter addition significantly increased soil CO by 12% in the Mixed forests ( P=0.02) but not in both Camphor tree and Masson pine forests ( P>0.05), when compared with their corresponding control treatments. However, litter addition increased soil FCO rates in the months of June-August in Camphor tree and Masson pine forests, coinciding with high soil temperature of summer conditions. Litter exclusion reduced soil FCO more than litter addition increased it in the study sites. Responses of soil respiration to litter input treatments varied with forest types. Litter input treatments did not alter the seasonal patterns of soil temperature and soil water content. Our results indicated that changes in aboveground litter as a result of global climate change and/or forest management have a great potential to alter soil respiration and soil carbon balance in forest ecosystems. [ABSTRACT FROM AUTHOR]

The ignition delay of n-heptane homogeneous charge compression ignition (HCCI) combustion under high levels of carbon dioxide addition was quantitatively measured at elevated pressure from low to intermediate temperatures in a rapid compression machine. The experiments were conducted in the compressed temperature range 613-750 K. Both the compression ratio and fuel/air equivalence ratio were varied to investigate their effects on the ignition delay of n-heptane. Carbon dioxide was subsequently added to study the influence of the carbon dioxide level on the ignition delay of n-heptane under low-temperature conditions. It was found that carbon dioxide had different effects on the two -stages of ignition delay of n-heptane under low-temperature conditions: the concentration of carbon dioxide had little effect on the first-stage ignition time; a certain concentration of carbon dioxide accelerated the first-stage ignition but had a significantly larger impact on the second-stage ignition delay, thus increasing the overall ignition delay time. The results also showed that the first-stage ignition delay of n-heptane is only a function of temperature under low-temperature conditions. The mass of n-heptane in the combustible mixture, the equivalence ratio, and the pressure at the top dead center had little effect on the first-stage ignition time of n-heptane. [ABSTRACT FROM AUTHOR]

We used molecular dynamics simulation to demonstrate the microscopic wetting behavior of two solid model surfaces for the first time. Hydrophilic and hydrophobic features were modeled in a dense CO2 fluid environment under various densities. The water droplet loses contact with the surface under the influence of higher density CO2 fluids on the hydrophobic surface. For the hydrophilic surface, no separation between the water droplet and the surface was observed. However, the contact angle of the water droplet on the hydrophilic surface was found to increase with the fluid density. The effect of dense CO2 fluid on the surface wettability can be interpreted in terms of enhanced interactions from the surrounding CO2 molecules. [ABSTRACT FROM AUTHOR]

Fluid and melt inclusions in mantle xenoliths are thought as direct samples to study mantle liquids. Here we apply Raman microspectroscopy and microthermometry to fluid/melt inclusions in lherzolite xenoliths in Qiaoshan basalts, a Miocene volcano in Linqu, Shandong Province, eastern China. These inclusions include (1) early CO2 fluid inclusions, (2) early carbonate melt inclu- sions, (3) late CO2 fluid inclusions, and (4) late silicate melt inclusions. Among the early CO2 fluid inclusions, most consist of high-density pure CO2, while others have small amounts of other components besides of CO2, including graphite, magnesite, Mg-calcite, CO and N2. The lowest trapping pressures are estimated to be 1.42 GPa and 0.80 GPa for the early and the late fluid inclusions, respectively. Because orthopyroxene is the main host mineral for the early carbonate melt inclusions, we propose that the formation of these carbonate melts is genetically associated with the interactions between CO2 fluids and silicate minerals, e.g. olivine and clinopyroxene. The diversity of minor components in the early CO2 fluid inclusions indicates that mantle peridotites had undergone redox reactions with penetrating fluids/melts. These observations suggest that the compositions of the lithospheric mantle beneath the studied area had been changed by asthenosphere-derived CO2-rich fluids/melts. [ABSTRACT FROM AUTHOR]

The response of ENSO frequency to the increasing CO2 concentration and associated mechanism are examined with outputs of four coupled climate models (GFDL/CM2.0, CNRM/CM3, IPSL/CM4 and INM/CM3.0) submitted to the IPCC Fourth Assessment Report (IPCC AR4). Results reveal a significant change of ENSO frequency as response to the increasing CO2 concentration. However, such a change exhibits an evident model dependence. The ENSO frequency tends to increase in GFDL/CM2.0 and CNRM/CM3 models and decreases in IPSL/CM4 and INM/CM3.0 models. The model dependence is found to be determined by how the model climatological background state of the tropical Pacific responds to the increasing CO2 concentration. It is demonstrated that the change of zonally- and vertically-averaged climatological background upper ocean temperature gradient between the equator and off-equator is crucially responsible for the ENSO frequency change. As response to the increasing CO2 concentration, the climatological background temperature gradient is increased in GFDL/CM2.0 and CNRM/CM3 models and decreased in IPSL/CM4 and INM/CM3.0 models. In terms of the recharge-discharge oscillator theory for ENSO, the increased (decreased) climatological background temperature gradient between the equator and off-equator induces a faster (slower) exchange of oceanic heat content between the equator and off-equator, thus giving rise to a shorter (longer) ENSO timescale and a higher (lower) ENSO frequency. [ABSTRACT FROM AUTHOR]

With density functional theory, the mechanism of water-enhanced CO oxidation on oxygen pre-covered Au (111) surface is theoretically studied. First, water is activated by the pre-covered oxygen atom and dissociates to OH[subads] group. Then, OH[subads] reacts with CO[subads] to form chemisorbed HOCO[subads]. Finally, with the aid of water, HOCO[subads] dissociates to CO[sub2]. The whole process can be described as 1/2H[sub2]O[subads] + H[sub2]O[subads] + 1/2O[subads]+ CO[subads]→H[sub3]O[subads] + CO[sub2], gasP One CO[sub2] is formed with only 1/2 pre-covered oxygen atom. That is why more CO[sub2] is observed when water is present on oxygen pre-covered Au (111) surface. Activation energy of each elementary step is low enough to allow the reaction to proceed at low temperature. [ABSTRACT FROM AUTHOR]

To measure contact angle between CO2 and solid surface, in this study a visual high-pressure vessel has been developed, with a corresponding well-controlled constant temperature system. Pendant drop method is applied to the investigation of the contact angles of CO2 on a stainless steel surface in its own vapor. The image of the pendant drop is recorded by a camera, and a B-Snake method is used to analyze the contour and the contact angle of the droplet. The experimental results have provided a set of well tested data, which show that CO2 has good infiltration into stainless steel surface and the developed method can be used as a standard testing one for measuring the contact angle between high-pressure liquid and solid surface. [ABSTRACT FROM AUTHOR]

Using the eddy covariance method, from 1 July 2003 to 30 June 2004, we conducted the observation and analysis of ecosystem CO2 flux in 3 types of alpine meadow vegetation (Kobresia humilis, Potentilla fruticosa shrub and Kobresia tibetica swamp meadows) on the Qinghai-Tibetan Plateau. The results show that the Kobresia humilis meadow, the shrub meadow and the swamp meadow's highest CO2 uptake rates are 16.78, 10.42 and 16.57 µmol·m-2·s-1 respectively, while their highest CO2 release rates are 8.22, 7.73 and 18.67 µmol·m-2·s-1 respectively. The Kobresia humilis meadow and shrub meadow's annual atmospheric uptakes are 282 g CO2/m² and 53 g CO2/m², respectively, while swamp meadow's annual atmospheric release is 478 g CO2/m². This proves that the Kobresia humilis meadow and the shrub meadow on the Qinghai-Tibetan Plateau have relatively low potential for CO2 uptake and release compared to C4 grasslands, a number of lowland grasslands, and forests. Moreover, swamp meadow has relatively high release potential. This, in turn, reveals clear differences in carbon source/sink between different types of vegetation in the Qinghai-Tibetan Plateau alpine meadow ecosystem. These differences are mainly brought by differences in the vegetations' photosynthetic capacity and soil respiration. [ABSTRACT FROM AUTHOR]

Response of the Atlantic thermohaline circulation (THC) to global warming is examined by using the climate system model developed at IAP/LASG. The evidence indicates that the gradually warming climate associated with the increased atmospheric carbon dioxide leads to a warmer and fresher sea surface water at the high latitudes of the North Atlantic Ocean, which prevents the down-welling of the surface water. The succedent reduction of the pole-toequator meridional potential density gradient finally results in the decrease of the THC in intensity. When the atmospheric carbon dioxide is doubled, the maximum value of the Atlantic THC decreases approximately by 8%. The associated poleward oceanic heat transport also becomes weaker. This kind of THC weakening centralizes mainly in the northern part of the North Atlantic basin, indicating briefly a local scale adjustment rather than a loop oscillation with the whole Atlantic "conveyor belt" decelerating. [ABSTRACT FROM AUTHOR]

Presents a study which examined the reliability of using tree-ring isotope ratio to reconstruct the atmospheric carbon dioxide levels. Methodology; Results; Discussion.

Discusses the responses of plant rhizosphere to atmospheric carbon dioxide enrichment. Functions of chemicals to soil released during growth of plant root; Changes of microbials in the rhizosphere and their roles in trace greenhouse gases release; Conclusions.