Littérature scientifique sur le sujet « CO2 fluxe »
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Articles de revues sur le sujet "CO2 fluxe"
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Jamali, H., S. J. Livesley, L. B. Hutley, B. Fest et S. K. Arndt. « The relationships between termite mound CH<sub>4</sub>/CO<sub>2</sub> ; emissions and internal concentration ratios are species specific ». Biogeosciences 10, no 4 (5 avril 2013) : 2229–40. http://dx.doi.org/10.5194/bg-10-2229-2013.
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Abstract. We investigated the relative importance of CH4 and CO2 fluxes from soil and termite mounds at four different sites in the tropical savannas of northern Australia near Darwin and assessed different methods to indirectly predict CH4 fluxes based on CO2 fluxes and internal gas concentrations. The annual flux from termite mounds and surrounding soil was dominated by CO2 with large variations among sites. On a carbon dioxide equivalent (CO2-e) basis, annual CH4 flux estimates from termite mounds were 5- to 46-fold smaller than the concurrent annual CO2 flux estimates. Differences between annual soil CO2 and soil CH4 (CO2-e) fluxes were even greater, soil CO2 fluxes being almost three orders of magnitude greater than soil CH4 (CO2-e) fluxes at site. The contribution of CH4 and CO2 emissions from termite mounds to the total CH4 and CO2 emissions from termite mounds and soil in CO2-e was less than 1%. There were significant relationships between mound CH4 flux and mound CO2 flux, enabling the prediction of CH4 flux from measured CO2 flux; however, these relationships were clearly termite species specific. We also observed significant relationships between mound flux and gas concentration inside mound, for both CH4 and CO2, and for all termite species, thereby enabling the prediction of flux from measured mound internal gas concentration. However, these relationships were also termite species specific. Using the relationship between mound internal gas concentration and flux from one species to predict mound fluxes from other termite species (as has been done in the past) would result in errors of more than 5-fold for mound CH4 flux and 3-fold for mound CO2 flux. This study highlights that CO2 fluxes from termite mounds are generally more than one order of magnitude greater than CH4 fluxes. There are species-specific relationships between CH4 and CO2 fluxes from a mound, and between the inside mound concentration of a gas and the mound flux emission of the same gas, but these relationships vary greatly among termite species. Thus, there is no generic relationship that will allow for the accurate prediction of CH4 fluxes from termite mounds of all species, but given the data limitations, the above methods may still be used with caution.
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Jamali, H., S. J. Livesley, L. B. Hutley, B. Fest et S. K. Arndt. « The relationship between termite mound CH<sub>4</sub>/CO<sub>2</sub> ; emissions and internal concentration ratios are species specific ». Biogeosciences Discussions 9, no 12 (7 décembre 2012) : 17313–45. http://dx.doi.org/10.5194/bgd-9-17313-2012.
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Abstract. 1. We investigated the relative importance of CH4 and CO2 fluxes from soil and termite mounds at four different sites in the tropical savannas of Northern Australia near Darwin and assessed different methods to indirectly predict CH4 fluxes based on CO2 fluxes and internal gas concentrations. 2. The annual flux from termite mounds and surrounding soil was dominated by CO2 with large variations among sites. On a CO2-e basis, annual CH4 flux estimates from termite mounds were 5- to 46-fold smaller than the concurrent annual CO2 flux estimates. Differences between annual soil CO2 and soil CH4 (CO2-e) fluxes were even greater, soil CO2 fluxes being almost three orders of magnitude greater than soil CH4 (CO2-e) fluxes at site. 3. There were significant relationships between mound CH4 flux and mound CO2 flux, enabling the prediction of CH4 flux from measured CO2 flux, however, these relationships were clearly termite species specific. 4. We also observed significant relationships between mound flux and gas concentration inside mound, for both CH4 and CO2, and for all termite species, thereby enabling the prediction of flux from measured mound internal gas concentration. However, these relationships were also termite species specific. Using the relationship between mound internal gas concentration and flux from one species to predict mound fluxes from other termite species (as has been done in past) would result in errors of more than 5-fold for CH4 and 3-fold for CO2. 5. This study highlights that CO2 fluxes from termite mounds are generally more than one order of magnitude greater than CH4 fluxes. There are species-specific relationships between CH4 and CO2 fluxes from a~mound, and between the inside mound concentration of a gas and the mound flux emission of the same gas, but these relationships vary greatly among termite species. Consequently, there is no generic relationship that will allow for the prediction of CH4 fluxes from termite mounds of all species.
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Hirsch, A. I. « On using radon-222 and CO<sub>2</sub> ; to calculate regional-scale CO<sub>2</sub> ; fluxes ». Atmospheric Chemistry and Physics Discussions 6, no 6 (2 novembre 2006) : 10929–58. http://dx.doi.org/10.5194/acpd-6-10929-2006.
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Abstract. Because of its ubiquitous release on land and well-characterized atmospheric loss, radon-222 has been very useful for deducing fluxes of greenhouse gases such as CO2, CH4, and N2O. It is shown here that the radon-tracer method, used in previous studies to calculate regional-scale greenhouse gas fluxes, returns a weighted-average flux (the flux field F weighted by the sensitivity of the measurements to that flux field, f) rather than an evenly-weighted spatial average flux. A synthetic data study using a Lagrangian particle dispersion model and modeled CO2 fluxes suggests that the discrepancy between the sensitivity-weighted average flux and evenly-weighted spatial average flux can be significant in the case of CO2, due to covariance between F and f for biospheric CO2 fluxes during the growing season and also for anthropogenic CO2 fluxes in general. A technique is presented to correct the radon-tracer derived fluxes to yield an estimate of evenly-weighted spatial average CO2 fluxes. A new method is also introduced for correcting the CO2 flux estimates for the effects of radon-222 radioactive decay in the radon-tracer method.
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Hirsch, A. I. « On using radon-222 and CO<sub>2</sub> ; to calculate regional-scale CO<sub>2</sub> ; fluxes ». Atmospheric Chemistry and Physics 7, no 14 (17 juillet 2007) : 3737–47. http://dx.doi.org/10.5194/acp-7-3737-2007.
Texte intégralRésumé :
Abstract. Because of its ubiquitous release on land and well-characterized atmospheric loss, radon-222 has been very useful for deducing fluxes of greenhouse gases such as CO2, CH4, and N2O. It is shown here that the radon-tracer method, used in previous studies to calculate regional-scale greenhouse gas fluxes, returns a weighted-average flux (the flux field F weighted by the sensitivity of the measurements to that flux field, f) rather than an evenly-weighted spatial average flux. A synthetic data study using a Lagrangian particle dispersion model and modeled CO2 fluxes suggests that the discrepancy between the sensitivity-weighted average flux and evenly-weighted spatial average flux can be significant in the case of CO2, due to covariance between F and f for biospheric CO2 fluxes during the growing season and also for anthropogenic CO2 fluxes in general. A technique is presented to correct the radon-tracer derived fluxes to yield an estimate of evenly-weighted spatial average CO2 fluxes. A new method is also introduced for correcting the CO2 flux estimates for the effects of radon-222 radioactive decay in the radon-tracer method.
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Dong, Yuanxu, Mingxi Yang, Dorothee C. E. Bakker, Vassilis Kitidis et Thomas G. Bell. « Uncertainties in eddy covariance air–sea CO<sub>2</sub> ; flux measurements and implications for gas transfer velocity parameterisations ». Atmospheric Chemistry and Physics 21, no 10 (26 mai 2021) : 8089–110. http://dx.doi.org/10.5194/acp-21-8089-2021.
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Abstract. Air–sea carbon dioxide (CO2) flux is often indirectly estimated by the bulk method using the air–sea difference in CO2 fugacity (ΔfCO2) and a parameterisation of the gas transfer velocity (K). Direct flux measurements by eddy covariance (EC) provide an independent reference for bulk flux estimates and are often used to study processes that drive K. However, inherent uncertainties in EC air–sea CO2 flux measurements from ships have not been well quantified and may confound analyses of K. This paper evaluates the uncertainties in EC CO2 fluxes from four cruises. Fluxes were measured with two state-of-the-art closed-path CO2 analysers on two ships. The mean bias in the EC CO2 flux is low, but the random error is relatively large over short timescales. The uncertainty (1 standard deviation) in hourly averaged EC air–sea CO2 fluxes (cruise mean) ranges from 1.4 to 3.2 mmolm-2d-1. This corresponds to a relative uncertainty of ∼ 20 % during two Arctic cruises that observed large CO2 flux magnitude. The relative uncertainty was greater (∼ 50 %) when the CO2 flux magnitude was small during two Atlantic cruises. Random uncertainty in the EC CO2 flux is mostly caused by sampling error. Instrument noise is relatively unimportant. Random uncertainty in EC CO2 fluxes can be reduced by averaging for longer. However, averaging for too long will result in the inclusion of more natural variability. Auto-covariance analysis of CO2 fluxes suggests that the optimal timescale for averaging EC CO2 flux measurements ranges from 1 to 3 h, which increases the mean signal-to-noise ratio of the four cruises to higher than 3. Applying an appropriate averaging timescale and suitable ΔfCO2 threshold (20 µatm) to EC flux data enables an optimal analysis of K.
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Cui, Hang. « Greenhouse gas emission fluxes from peat bogs in the Arak Lake Basin in 2021 ». IOP Conference Series : Earth and Environmental Science 937, no 2 (1 décembre 2021) : 022035. http://dx.doi.org/10.1088/1755-1315/937/2/022035.
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Abstract Climate change has an important impact on greenhouse gas emissions from wetland ecosystems. The static box-meteorological chromatography method was used to determine the CO2 and CH4 emission fluxes of hummocky and hollow in the peat bogs in the Arak Lake Basin during the growing season in 2021. The results showed that the peaks of the CO2 and CH4 emission fluxes in the growing seasons of the hummocky and hollow appeared in July, and their value in May is the lowest. The average C02 emission flux (376.39±56.14 mg-m-2-h-1) during the growing season of hummocky is higher than that of hollow (167.36 mg-m-2-h-1), while the average emission flux of CH4 during the growing season of hummocky (2.00±0.31 mg-m-2-h-1) is lower than that of hollow (3.04 mg-m-2-h-1). The climatic fluctuations have caused differences in the CO2 and CH4 emission fluxes of the same micro-topography in the study area during the growing season between 2020 and 2021.
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Ishidoya, Shigeyuki, Hirofumi Sugawara, Yukio Terao, Naoki Kaneyasu, Nobuyuki Aoki, Kazuhiro Tsuboi et Hiroaki Kondo. « O<sub>2</sub> ; : CO<sub>2</sub> ; exchange ratio for net turbulent flux observed in an urban area of Tokyo, Japan, and its application to an evaluation of anthropogenic CO<sub>2</sub> ; emissions ». Atmospheric Chemistry and Physics 20, no 9 (15 mai 2020) : 5293–308. http://dx.doi.org/10.5194/acp-20-5293-2020.
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Abstract. In order to examine O2 consumption and CO2 emission in a megacity, continuous observations of atmospheric O2 and CO2 concentrations, along with CO2 flux, have been carried out simultaneously since March 2016 at the Yoyogi (YYG) site located in the middle of Tokyo, Japan. An average O2 : CO2 exchange ratio for net turbulent O2 and CO2 fluxes (ORF) between the urban area and the overlaying atmosphere was obtained based on an aerodynamic method using the observed O2 and CO2 concentrations. The yearly mean ORF was found to be 1.62, falling within the range of the average OR values of liquid and gas fuels, and the annual average daily mean O2 flux at YYG was estimated to be −16.3 µmol m−2 s−1 based on the ORF and CO2 flux. By using the observed ORF and CO2 flux, along with the inventory-based CO2 emission from human respiration, we estimated the average diurnal cycles of CO2 fluxes from gas and liquid fuel consumption separately for each season. Both the estimated and inventory-based CO2 fluxes from gas fuel consumption showed average diurnal cycles with two peaks, one in the morning and another one in the evening; however, the evening peak of the inventory-based gas consumption was much larger than that estimated from the CO2 flux. This can explain the discrepancy between the observed and inventory-based total CO2 fluxes at YYG. Therefore, simultaneous observations of ORF and CO2 flux are useful in validating CO2 emission inventories from statistical data.
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Itoh, Masayuki, Yoshiko Kosugi, Satoru Takanashi, Shuhei Kanemitsu, Ken'ichi Osaka, Yuki Hayashi, Makoto Tani et Abdul Rahim Nik. « Effects of soil water status on the spatial variation of carbon dioxide, methane and nitrous oxide fluxes in tropical rain-forest soils in Peninsular Malaysia ». Journal of Tropical Ecology 28, no 6 (novembre 2012) : 557–70. http://dx.doi.org/10.1017/s0266467412000569.
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Abstract:To assess the effects of soil water status on the spatial variation in soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes, we examined these gas fluxes and environmental factors in a tropical rain forest in Peninsular Malaysia. Measurements of soil CO2, CH4 and N2O fluxes were taken ten, nine, and seven times, respectively over 30 mo at 15 or 39 sampling point within 2-ha plot. Mean (± SE) value of spatially averaged CO2 flux was 4.70 ± 0.19 μmol CO2 m−2 s−1 and observed spatial variation in CO2 flux was negatively related to the volumetric soil water content (VSWC) during the dry period. Over the wet period, extremely high CO2 emissions were positively correlated with VSWC at some locations, suggesting that no spatial structure of CO2 flux was because of such hot-spot CO2 emissions. Flux of CH4 was usually negative with little variation, with a mean value of –0.49 ± 0.15 mg CH4 m−2 d−1, resulting in the soil at our study site functioning as a CH4 sink. Spatial variation in CH4 flux was positively related to the VSWC throughout the entire study period (dry and wet). Some CH4 hot spots were observed during dry periods, probably due to the presence of termites. Mean value of spatially averaged N2O flux was 98.9 ± 40.7 μg N m−2 h−1 and N2O flux increased markedly during the wet period. Spatially, N2O flux was positively related to both the VSWC and the soil N concentration and was higher in wet and anaerobic soils. These findings suggest that denitrification is a major contributor to high soil N2O fluxes. Additionally, analysis by adjusting confounding effects of time, location and interaction between time and location in mixed models, VSWC has a negative effect on CO2 flux and positive effects on CH4 and N2O fluxes. We found that soil water status was related temporally to rainfall and controlled greenhouse gas (GHG) fluxes from the soil at the study site via several biogeochemical processes, including gas diffusion and soil redox conditions. Our results also suggest that considering the biological effects such as decomposer activities may help to explain the complex temporal and spatial patterns in CO2 and CH4 fluxes.
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Erkkilä, Kukka-Maaria, Anne Ojala, David Bastviken, Tobias Biermann, Jouni J. Heiskanen, Anders Lindroth, Olli Peltola, Miitta Rantakari, Timo Vesala et Ivan Mammarella. « Methane and carbon dioxide fluxes over a lake : comparison between eddy covariance, floating chambers and boundary layer method ». Biogeosciences 15, no 2 (19 janvier 2018) : 429–45. http://dx.doi.org/10.5194/bg-15-429-2018.
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Abstract. Freshwaters bring a notable contribution to the global carbon budget by emitting both carbon dioxide (CO2) and methane (CH4) to the atmosphere. Global estimates of freshwater emissions traditionally use a wind-speed-based gas transfer velocity, kCC (introduced by Cole and Caraco, 1998), for calculating diffusive flux with the boundary layer method (BLM). We compared CH4 and CO2 fluxes from BLM with kCC and two other gas transfer velocities (kTE and kHE), which include the effects of water-side cooling to the gas transfer besides shear-induced turbulence, with simultaneous eddy covariance (EC) and floating chamber (FC) fluxes during a 16-day measurement campaign in September 2014 at Lake Kuivajärvi in Finland. The measurements included both lake stratification and water column mixing periods. Results show that BLM fluxes were mainly lower than EC, with the more recent model kTE giving the best fit with EC fluxes, whereas FC measurements resulted in higher fluxes than simultaneous EC measurements. We highly recommend using up-to-date gas transfer models, instead of kCC, for better flux estimates. BLM CO2 flux measurements had clear differences between daytime and night-time fluxes with all gas transfer models during both stratified and mixing periods, whereas EC measurements did not show a diurnal behaviour in CO2 flux. CH4 flux had higher values in daytime than night-time during lake mixing period according to EC measurements, with highest fluxes detected just before sunset. In addition, we found clear differences in daytime and night-time concentration difference between the air and surface water for both CH4 and CO2. This might lead to biased flux estimates, if only daytime values are used in BLM upscaling and flux measurements in general. FC measurements did not detect spatial variation in either CH4 or CO2 flux over Lake Kuivajärvi. EC measurements, on the other hand, did not show any spatial variation in CH4 fluxes but did show a clear difference between CO2 fluxes from shallower and deeper areas. We highlight that while all flux measurement methods have their pros and cons, it is important to carefully think about the chosen method and measurement interval, as well as their effects on the resulting flux.
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Peng, Z., M. Zhang, X. Kou, X. Tian et X. Ma. « A regional carbon flux data assimilation system and its preliminary evaluation in East Asia ». Atmospheric Chemistry and Physics Discussions 14, no 14 (8 août 2014) : 20345–81. http://dx.doi.org/10.5194/acpd-14-20345-2014.
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Abstract. In order to optimize surface CO2 fluxes at finer scales, a regional surface CO2 flux inversion system (Carbon Flux Inversion system and Community Multi-scale Air Quality, CFI-CMAQ) has been developed by simultaneously assimilating CO2 concentrations and surface CO2 fluxes into the regional modeling system, CMAQ. The smoothing operator is associated with the atmospheric transport model to constitute a persistence dynamical model to forecast the surface CO2 flux scaling factors. In this implementation, the "signal-to-noise" problem can be avoided; plus, any useful observed information achieved by the current assimilation cycle can be transferred into the next assimilation cycle. Thus, the surface CO2 fluxes can be optimized as a whole at the grid scale in CFI-CMAQ. The performance of CFI-CMAQ was quantitatively evaluated through a set of Observing System Simulation Experiments (OSSEs) by assimilating CO2 retrievals from GOSAT (Greenhouse Gases Observing Satellite). The results showed that the CO2 concentration assimilation using the ensemble Kalman filter (EnKF) could constrain the CO2 concentrations effectively, illustrating that the simultaneous assimilation of CO2 concentrations can provide convincing CO2 initial analysis fields for CO2 flux inversion. In addition, the CO2 flux optimization using the ensemble Kalman smoother (EnKS) demonstrated that CFI-CMAQ could in general reproduce true fluxes at finer scales with acceptable bias. Two further sets of numerical experiments were conducted to investigate the sensitivities of the inflation factor of scaling factors and the smoother window. The results showed that the ability of CFI-CMAQ to optimize CO2 fluxes greatly relied on the choice of the inflation factor. However, the smoother window had a slight influence on the optimized results. CFI-CMAQ performed very well even with a short lag-window (e.g. 3 days).
Thèses sur le sujet "CO2 fluxe"
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SILVA, Paulo Ferreira da. « Fluxos de CO2, água e energia em pastagens e caatinga no semiárido pernambucano ». Universidade Federal Rural de Pernambuco, 2015. http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/6574.
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The natural vegetation of Caatinga is relatively well adapted and tolerant to drought and to high temperatures. It is known that forest conversions to pasture and/or crop cultivation are human interventions, which affect energy exchanges, water and carbon between land surface and the atmosphere. However, up to the present moment, there is no study measuring these fluxes in the caatinga and pastures areas in the Brazilian semiarid lands. Thus, this paper aimed at determining the fluxes of energy, H2O and CO2 in areas of caatinga and pastures, as well as at analyzing the seasonal variability patterns of these fluxes. The land activities were carried out in two areas, one of them located on the Buenos Aires farm (7° 59’ 31’’ S and 38° 17’ 59’’ O), and the other located on the Lagoinha farm (07° 56’ 50,4’’ S and 38° 23’ 29’’ O), cultivated with pasture of grass chain (Urochloa mosambicensis), both properties located in the city of Serra Talhada, state of Pernambuco, Brazil. In order to determine the fluxes of energy, H2O and CO2, a methodology of correlation of swirls was adopted, by means of micrometeorological towers, installed in the center of each experimental area. Along with the index of foliar area, we have also measured the aboveground phytomass of both the pasture and the caatinga herbaceous vegetation, as well as water storage in the soil, by means of TDR sensors. On the basis of the results, it has been found that the maximum production of dry pasture mass was in the order of 2,208 kg ha-1 and annual average of 832 kg ha-1. On the other hand, the caatinga dry mass was in the order of 2,559 kg ha-1 and the annual average was 626 kg ha-1. Water storage in the soil (0-40 cm) of pasture was 29% greater than the one of the caatinga. This fact was possibly attributed to the interception of rain by the caatinga canopy. In relation the fluxes of energy, radiation balance (Rb) was used mainly as sensitive flow of heat (H), with 51% in the pasture and 47% in the caatinga. The fraction of Rb used as flow of latent heat (LE) was of 23% in the pasture and 32% in the caatinga. In relation to the evapotranspiration, the caatinga had total values (523 mm) and average values (1,4 mm d-1) greater than the pasture (389 mm and 1,1 mm d-1), possibly due to the greater depth of its radicular system. During the experimental period, the fluxes of daily average CO2 were ˗ 0,91 and ˗ 0,68 μmol m-2 s-1 for the caatinga and the pasture, respectively. Not only during the rainy season but also the dry season, the vegetation acted as atmospheric CO2 sink. The caatinga was more efficient than the pasture, sequestrating in average 14,6 kg of C ha-1 d-1, during the rainy season and 4,3 kg of C ha-1 d-1, in the dry season, while the pasture sequestrated 11,7 kg of C ha-1 d-1, in the rainy season and 2,5 kg of C ha-1 d-1, in the dry season. The caatinga has proved more efficient than the pasture in using soil water (greater ET) and in sequestrating atmospheric CO2.
A vegetação natural da Caatinga é relativamente bem adaptada e tolerante à seca e a altas temperaturas. Sabe-se que a conversão de florestas em pastagens e/ou cultivo de lavouras são intervenções humanas que afetam as trocas de energia, água e carbono entre a superfície da terra e a atmosfera. No entanto, até o momento não se tem nenhum estudo medindo esses fluxos em áreas de caatinga e de pastagens no semiárido brasileiro. Desse modo, este trabalho teve como objetivo determinar os fluxos de energia, H2O e CO2 em áreas de caatinga e de pastagens, além de analisar os padrões de variabilidade sazonal desses fluxos. A s atividades de campo foram realizadas em duas áreas, sendo uma localizada na Fazenda Buenos Aires (7º 59’ 31” S e 38º 17’ 59” O) e a outra localizada na Fazenda Lagoinha (07° 56’ 50,4”S e 38° 23’ 29” O), cultivada com a pastagem capim corrente (Urochloa mosambicensis), ambas propriedades localizadas no Município de Serra Talhada PE. Para a determinação dos fluxos de energia, H2O e CO2 foi usada a metodologia da correlação dos turbilhões, por meio de torres micrometeorológicas instaladas no centro de cada área experimental. Foram medidos o índice de área foliar e a biomassa áerea da pastagem e da vegetação herbácea da caatinga e o armazenamento de água no solo, por meio de sensores TDR. Dos resultados, verificou-se que a produção máxima de massa seca da pastagem foi de 2.208 kg ha-1 e média anual de 832 kg ha-1, já a massa seca máxima da caatinga foi de 2.559 kg ha-1 e a média anual de 626 kg ha-1. O armazenamento de água no solo (0-40 cm) da pastagem foi 29% maior que da caatinga, possivelmente devido a interceptação da chuva pelo dossel da caatinga. Com relação aos fluxos de energia, o saldo de radiação (Rn) foi utilizado principalmente como fluxo de calor sensível (H), com 51% na pastagem e 47% na caatinga. A fração do Rn usada como fluxo de calor latente (LE) foi de 23% na pastagem e 32% na caatinga. Com relação a evapotranspiração, a caatinga teve valores totais (523 mm) e médios (1,4 mm d-1) maiores que a pastagem (389 mm e 1,1 mm d-1), possivelmente, devido a maior profundidade de seu sistema radicular. Durante o período experimental os fluxos de CO2 médios diários foram de -0,91 e -0,68 mol m-2 s-1 para a caatinga e a pastagem, respectivamente. Tanto na estação chuvosa quanto na estação seca, ambas as vegetações atuaram como sumidouro de CO2 atmosférico. A caatinga foi mais eficiente que a pastagem, sequestrando em média 14,6 kg de C ha-1 d-1, na estação chuvosa e 4,3 kg de C ha-1 d-1, na estação seca; enquanto a pastagem sequestrou 11,7 kg de C ha-1 d-1, na estação chuvosa e 2,5 kg de C ha-1 d-1, na estação seca. A caatinga demonstrou ser mais eficiente em usar a água do solo (maior ET) e sequestrar CO2 atmosférico que a pastagem.
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RIBEIRO, Apolo Alves. « Fluxos de CO2 e de vapor d’água em feijão cultivado no agreste meridional pernambucano ». Universidade Federal Rural de Pernambuco, 2014. http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/6645.
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
Many important processes occurring in ecosystems, such as photosynthesis and productivity of vegetation, are associated with the exchange of CO2, water and energy. Accurate measurement of these fluxes are therefore fundamental to a broad understanding of the carbon cycle in terrestrial ecosystems. However, no such study was conducted under the conditions of the Agreste of Pernambuco, with the bean crop. Given the above, this study aimed to quantify the water, energy and CO2 fluxes in soil cultivated with bean under rainfed conditions. The study was conducted in a bean producing area of the city of São João, where were installed sensors to measure these fluxes, using the energy balance method - eddy covariance (energy and CO2 fluxes) and soil water balance method (water fluxes) in the period from 31/05/2013 to 08/20/2013. In addition to these measurements were also measured height, leaf area index (LAI) and the bean yield. Regarding the components of the water balance was found that the flow of water at a depth of 35 cm (deep drainage and/or capillarity rise) had very low values. It was also observed that the periods of high rainfall resulted in higher water storage in soil and increased evapotranspiration (ET). The ET obtained by water balance method had a total and average values of 146.0 mm and 1.78 mm d-1, respectively. The bean presented its highest water consumption during the reproductive period (29/06/2013 to 29/07/2013), with an average value of 2.55 mm d-1. Regarding the energy fluxes, it was found that the latent heat flux (LE) consumed on average 78.46% of the radiation (Rn). The ET, measured by the eddy covariance method, was total value of 179.3 mm, with a mean value of 2.2 mm d-1. Bean yield was 2,050 kg ha-1, with water use efficiency of 1.16 kg m-3. Regarding the CO2 fluxes, it was observed that the same varied from -11.21 to -0.75 mol m-2 s-1, indicating the occurrence of carbon sequestration by the crop. On average, bean sequestered 54 kg C ha-1 per day, the equivalent to 3.3 t C ha-1 during the trial period.
Muitos processos importantes que ocorrem nos ecossistemas, tais como, a fotossíntese e a produtividade da vegetação, estão associados com as trocas de CO2, água e energia. Medições precisas desses fluxos são, portanto, fundamentais para uma ampla compreensão do ciclo do carbono em ecossistemas terrestres. No entanto, nenhum estudo desse tipo foi realizado nas condições do agreste meridional de Pernambuco, com a cultura do feijão. Diante do exposto, o presente trabalho objetivou quantificar os fluxos de água, de energia e de CO2 em solo cultivado com feijão sob condições de sequeiro. O trabalho foi realizado em uma área produtora de feijão do município de São João, onde se instalou sensores para medir esses fluxos, usando as metodologias do balanço de energia - correlação dos turbilhões (fluxos de energia e de CO2) e do balanço hídrico no solo (fluxos de água) no período de 31/05/2013 a 20/08/2013. Também foram determinadas a altura, o índice de área foliar (IAF) e a produtividade do feijão. Em relação aos componentes do balanço hídrico verificou-se que o fluxo de água (drenagem profunda e/ou ascensão capilar) na profundidade de 35 cm teve valores muito baixos, como também que os períodos de elevada pluviosidade resultaram em maior armazenamento de água no solo e maior evapotranspiração (ET). A ET do feijão pelo método do balanço hídrico teve valor total e médio de 146,0 mm e 1,78 mm d-1, respectivamente. A cultura apresentou seu maior consumo de água no período reprodutivo (29/06/2013 a 29/07/2013), com valor médio de 2,55 mm d-1. Quanto aos fluxos de energia, verificou-se que o fluxo de calor latente (LE) consumiu em média 78,46% do saldo de radiação (Rn). A ET medida pela metodologia da correlação dos turbilhões obteve valor total durante o período experimental de 179,3 mm, com média de 2,2 mm d-1. A produtividade do feijão foi de 2.050 kg ha-1, com eficiência do uso de água de 1,16 kg m-3. Em relação aos fluxos de CO2, observou-se que os mesmos variaram de -0,75 a -11,21 mol m-2 s-1, indicando a ocorrência de sequestro de carbono pelo feijão. Em média, o feijão sequestrou 54 kg de C ha-1 por dia, o equivalente a 3,3 t de C ha-1 durante o período experimental.
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Bianchi, Alejandro. « Sea-air CO2 fluxes in the Patagonia sea ». Paris 6, 2010. http://www.theses.fr/2010PA066613.
Texte intégralRésumé :
Les plateaux continentaux sont des régions très productives et pourraient constituer de régions de puits significatif de CO2 pour l’atmosphère. De 2000 à 2006, vingt-deux sections océanographiques sur le plateau continental de la Mer de Patagonie (Projets ARGAU et GEF PATAGONIA) ont permis d'étudier la variabilité saisonnière des différences de pression partielle de CO2 (pCO2) et des flux de CO2 (FCO2) entre la mer et l'atmosphère. Ce travail présente une analyse de l'influence des différentes variables environnementales et des processus physiques et biologiques sur les flux de CO2 à l’interface Océan-Atmosphère en mer de Patagonie. Malgré une variabilité saisonnière importante de pCO2 dans les eaux de surface, la mer de Patagonie constitue un puits pendant toutes les saisons. Dans ce plateau continental, le puits de CO2 est dû à des processus dynamiques (stratification, mélange vertical et fronts) et est intensifié par la pompe biologique. Il est montré que les diatomées sont beaucoup plus efficaces pour le pompage du CO2 que les dinoflagellées. Le premier bilan du CO2 (naturel et anthropique) pour l’Argentine montre que la mer de Patagonie capture une quantité de CO2 similaire aux émissions dues à la consommation d’énergie domestique.
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Vandeburie, Emile. « CO2-emissions from rivers and streams : Seasonal variation of pCO2-levels and CO2-fluxes ». Thesis, Mittuniversitetet, Institutionen för ekoteknik- och hållbart byggande, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-40804.
Texte intégralRésumé :
Since the industrial evolution, the CO2-levels have been increasing in a way that’s never seen in the history of the earth. To mitigate and adapt to the happening climate change it is really important to understand the global carbon cycle and each component that plays a role in it. Some studies suggest that there has been an underestimation on the influence from inland waters in the total carbon budget.To address this issue, there has been Eddy Covariance measurements going on the boreal Indalsälven river in front of the Kattstrupeforsen water dam. In this study continuous data has been collected which includes air-river CO2-flux, pCO2-values in the air and the water and some more meteorological parameters such as the wind speed, relative humidity and the air and water temperature. The aim of this study is to look into the seasonal variation in pCO2-levels and the CO2-fluxes on the Indalsälven river.The data indicates that the CO2-fluxes are mainly positive from January till July (average flux = 0.2 μmol m-2s-1) and mainly negative from September till November (average flux = -0.59 μmol m-2s-1) with an average flux of 0.212 μmol m-2s-1 during 2019. The main range of CO2-fluxes per month lies between -2 and 2 μmol m-2s-1, with the exception of March and December where there is a bigger range of fluxes. The pCO2-levels in the water mainly range between 400 and 1000 ppm. With the exception of 2 periods, one in the end of May where there is a peak to 4000ppm and more which can be explained by the spring flood and in the end of July and beginning of August where there is a peak to 3000 ppm.2020-06-17
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Molina, Carpio Luis. « Modélisation inverse des flux de CO2 en Amazonie ». Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLV040/document.
Texte intégralRésumé :
Une meilleure connaissance des variations saisonnières et interannuelles du cycle du carbone dans en Amazonie est essentielle afin de comprendre le rôle de cet écosystème dans le changement climatique. La modélisation atmosphérique inverse est un outil puissant pour estimer ces variations, en exploitant l'information sur la distribution spatiale et temporelle des flux de CO2 en surface contenue dans des observations de CO2 atmosphériques. Néanmoins, la confiance en les estimations des flux en Amazonie obtenues à partir des systèmes d'inversion mondiale est faible du fait du manque d'observations dans cette région.Dans ce contexte, j'ai d'abord analysé en détail les estimations de l'échange net de CO2 entre la biosphère et l'atmosphère (NEE) générées par deux inversions mondiales pour la période 2002 — 2010. Ces deux inversions ont assimilé des données provenant du réseau mondial d'observation du CO2 atmosphérique hors de l’Amérique du Sud, et une d'elles a assimilé des observations de quatre stations de surface en Amazonie, qui n'ont jamais été exploitées dans les études d'inversion précédentes. J'ai montré que dans une inversion mondiale les observations de stations loin d'Amazonie et les observations locales contrôlaient la NEE. Pourtant, les résultats ont révélé des structures à très grande échelle peu réalistes. L'analyse a confirmé le manque de stations en Amazonie pour fournir des estimations fiables, et les limites des systèmes d’inversion mondiale avec des modèles à très basse résolution.J'ai donc ensuite évalué l'apport de l'utilisation du modèle atmosphérique régional BRAMS, par rapport à celle du système mondial de prévision météorologique ECMWF, pour le forçage météorologique du modèle de transport atmosphérique CHIMERE simulant le CO2 en Amérique du Sud à haute résolution (~35 km). J'ai simulé le CO2 avec les deux modèles de transport―CHIMERE-BRAMS et CHIMERE-ECMWF. J'ai évalué ces simulations avec les profils verticaux de mesures aéroportées, en analysant les mesures individuelles et les gradients horizontaux de CO2 calculés entre paires de stations dans le sens du vent, à différentes altitudes ou intégrés sur la verticale. Les deux modèles de transport ont simulé les observations de CO2 avec une performance similaire, mais j'ai trouvé une importante incertitude sur les modèles de transport. Les mesures individuelles et les gradients horizontaux ont été surtout sensibles à la NEE, mais aussi, pendant la saison sèche, aux émissions des feux de biomasse (EFIRE). J'ai trouvé que l'assimilation des gradients horizontaux était plus approprié pour les inversions que celle des mesures individuelles, étant donné que les premiers ont été moins sensibles au signal associé aux flux hors de l'Amérique du Sud et à l'incertitude sur le modèle de transport en altitude.Finalement, j'ai développé deux systèmes d'inversion régionale pour l'Amérique du Sud tropicale avec les deux modèles de transport, et j'ai lancé des inversions avec quatre types de vecteurs d'observation: de mesures individuelles et gradients horizontaux sur cinq niveaux verticaux, à la surface, ou de gradients horizontaux intégrés sur la verticale. J'ai trouvé une forte dépendance des estimations des bilans régionaux et sub-régionaux de NEE et EFIRE au modèle de transport, ainsi qu'au vecteur d'observation. Les inversions assimilant des gradients horizontaux ont séparé mieux les signaux de NEE et EFIRE. Cependant, les grandes incertitudes sur les flux inversés ont réduit la confiance en ces estimations. Par conséquent, si mon étude n'a pas amélioré la connaissance des variations saisonnières et interannuelles de la NEE en Amazonie, elle a montré les besoins d'amélioration de la modélisation du transport dans la région et de la stratégie de modélisation inverse, du moins à travers une définition du vecteur d'observation appropriée qui prenne en compte les caractéristiques des données disponibles, et les limitations des modèles de transport actuelsA better knowledge of the seasonal and inter-annual variations of the Amazon carbon cycle is critical to understand the influence of this terrestrial ecosystem on climate change. Atmospheric inverse modeling is a powerful tool to estimate these variations by extracting the information on the spatio-temporal patterns of surface CO2 fluxes contained in observations of atmospheric CO2. However, the confidence in the Amazon flux estimates obtained from global inversion frameworks is low, given the scarcity of observations in this region.In this context, I started by analyzing in detail the Amazon net ecosystem exchange (NEE) inferred with two global inversions over the period 2002 — 2010. Both inversions assimilated data from the global observation network outside Amazonia, and one of them also assimilated data from four stations in Amazonia that had not been used in previous inversion efforts. I demonstrated that in a global inversion the observations from sites distant from Amazonia, as well as local observations, controlled the NEE inferred through the inversion. The inferred fluxes revealed large-scale structures likely not consistent with the actual NEE in Amazonia. This analysis confirmed the lack of observation sites in Amazonia to provide reliable flux estimates, and exposed the limitations of global frameworks, using low-resolution models to quantify regional fluxes. This limitations justified developing a regional approach.Then I evaluated the benefit of the regional atmospheric model BRAMS, relative to the global forecast system ECMWF, when both models provided the meteorological fields to drive the atmospheric transport model CHIMERE to simulate CO2 transport in tropical South America at high resolution (~35 km). I simulated the CO2 distribution with both transport models―CHIMERE-BRAMS and CHIMERE-ECMWF. I evaluated the model simulations with aircraft measurements in vertical profiles, analyzing the concentrations associated to the individual measurements, but also with horizontal gradients along wind direction between pairs of sites at different altitudes, or vertically integrated. Both transport models simulated the CO2 observations with similar performance, but I found a strong impact of the uncertainty in the transport models. Both individual measurements and horizontal gradients were most sensitive to NEE, but also to biomass burning CO2 emissions (EFIRE) in the dry season. I found that horizontal gradients were more suitable for inversions than individual measurements, since the former were less sensitive fluxes outside South America and further decreased the impact of the transport model uncertainty in altitude.Finally, I developed two analytical regional inversion systems for tropical South America, driven with CHIMERE-BRAMS and CHIMERE-ECMWF, and made inversions with four observation vectors: individual concentration measurements and horizontal gradients at five vertical levels, close to the surface, or horizontal gradients vertically integrated. I found a strong dependency of the inverted regional and sub-regional NEE and EFIRE emissions budgets on both the transport model and the observation vector. Inversions with gradients yielded a better separation of NEE and EFIRE signals. However, the large uncertainties in the inverted fluxes, did not yield high confidence in the estimates. Therefore, even though my study did not improve the knowledge of seasonal and year-to-year variations of the NEE in Amazonia, it demonstrated need of further efforts to improve transport modeling in the region and the inverse modeling strategy, at least through a careful definition of the observation vector that accounts for the characteristics of the available data, and the limitations of the current transport models
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Schneider, Julia [Verfasser]. « Dynamics of CO2 fluxes from boreal peatlands / Julia Schneider ». Greifswald : Universitätsbibliothek Greifswald, 2011. http://d-nb.info/1016213255/34.
Texte intégral
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Goret, Marine. « Etude des interactions entre le climat urbain et le CO2 : modélisation des flux de CO2 et application à l'échelle d'une ville ». Thesis, Toulouse, INPT, 2019. http://www.theses.fr/2019INPT0119.
Texte intégralRésumé :
Climat et CO2 sont intimement liés. Le lien entre les deux et si bien établi que les objectifs de limitation du réchauffement climatique s’expriment en quantité maximale d’équivalent CO2 que l’on s’autorise à émettre. La quantité de CO2 présente dans l’atmosphère à un instant donné est le résultat d’échanges et d’équilibres complexes entre l’atmosphère et la surface terrestre. Cette dernière est composée non seulement des océans, de la végétation et des sols naturels mais également des villes. Les échanges entre l’atmosphère et les surfaces urbaines proviennent majoritairement de quatre contributeurs : les émissions des bâtiments, le trafic routier, la respiration humaine et la végétation urbaine. Deux de ces contributeurs dépendent du climat : les bâtiments et la végétation. En effet, aux hautes et aux moyennes latitudes, les émissions des bâtiments sont fortement liées au chauffage, et fluctuent donc avec la température extérieure. La végétation quant à elle croît et s’épanouit plus ou moins vite en fonction des conditions météo-climatiques et plus particulièrement de la température, des précipitations et de l’ensoleillement. Le CO2 émit par la ville est ensuite transporté à travers l’atmosphère suivant la circulation atmosphérique locale qui est le résultat de la situation synoptique modifiée par la présence de la ville. Il existe donc, à l’échelle de la ville, des interactions fortes entre climat et CO2 : le bilan carbone de la ville dépend du climat local, et le transport du CO2 à travers l’atmosphère est influencé par la circulation atmosphérique induite par la ville. Cette thèse vise à étudier ces interactions. Pour cela, on a ajouté la modélisation des échanges de CO2 entre les surfaces urbaines et l’atmosphère dans le modèle de micro-climat urbain TEB. Cela a permis de vérifier que les processus physiques qui relient les émissions/captations de CO2 en ville et le climat urbain étaient bien identifiés et compris. Le modèle a été évalué sur deux cas d’étude permettant chacun d’évaluer plus spécifiquement l’un des contributeurs aux échanges de CO2 ville/atmosphère qui soit météosensible : les bâtiments sur le site de Toulouse, et la végétation sur le site de Kumpula (Finlande). Ces deux sites ont prouvé la capacité du modèle à reproduire les échanges de CO2 entre les surfaces urbaines et l’atmosphère ainsi que leurs cycles journaliers et saisonniers. Le site de Toulouse a souligné l’importance de connaître finement le comportement énergétique des habitants pour simuler les émissions de CO2 des bâtiments. Celui de Kumpula a démontré la capacité du modèle ISBA, conçu pour décrire les interactions entre la végétation en milieu non urbain et l’atmosphère, à décrire les échanges de CO2 entre la végétation urbaine et l’atmosphère. Le modèle, ainsi validé, a été utilisé pour réaliser des simulations d’émissions de CO2 par les bâtiments à l’échelle de l’ensemble de l’agglomération urbaine de Toulouse. Ces simulations ont mis à nouveau en évidence l’intérêt de la bonne connaissance des comportements énergétique des habitants : sur notre cas d’étude (quatre jours en hiver), l’abaissement de 2°C de la température de consigne du chauffage la nuit réduit de 33% les émissions de CO2. Lors de ces simulations, le transport du CO2 émis par la ville à travers l’atmosphère a également été suivi. On a ainsi mis en évidence que, malgré une situation météorologique de vent calme, le panache de CO2 créé par la ville se dissipe rapidement (moins d’une journée), ce qui limite l’augmentation de la concentration en CO2 au-dessus de la ville. Des simulations sur d’autres villes sont nécessaires pour savoir si ce résultat se généralise. Lors de cette thèse, on a étudié les interactions climat/CO2 à l’échelle d’une ville. Par la suite, il serait intéressant de réaliser des simulations en climat futur ou bien en mode couplé avec des modèles de climat afin d’étudier les rétroactions entre les liens climat/CO2 aux échelles locale et globaleClimate and CO2 are closely tied. The link between them is so well established that the objectives for global warming mitigation are expressed in terms of the maximum amount of CO2 equivalent that can be emitted. The amount of CO2 present in the atmosphere at a given time is the result of complex exchanges and equilibriums between the atmosphere and the earth's surface. The latter is composed not only of oceans, vegetation and natural soils, but also cities. Exchanges between the atmosphere and urban surfaces come mainly from four contributors: building emissions, road traffic, human respiration and urban vegetation. Two of these contributors depend on climate: buildings and vegetation. Buildings emissions, at least at high and medium latitudes, are strongly related to space heating, and therefore fluctuate with the outside temperature. As for the vegetation, its growth and open-up speed depends on the weather and climate conditions and more particularly on temperature, precipitation and solar radiation. The CO2 emitted by the city is then transported through the atmosphere by the local atmospheric circulation which is the result of the synoptic situation modified by the city's influence. Therefore there are strong interactions between climate and CO2 at the city scale: the city's carbon footprint depends on the local climate, and the transport of CO2 through the atmosphere is influenced by the atmospheric circulation induced by the city. The aim of this thesis is to study these interactions. That's why, the modeling of CO2 exchanges between urban surfaces and the atmosphere has been added to the urban micro-climate model TEB. This allows to verify that the physical processes that link CO2 emissions/uptakes in the city and the urban climate are well identified and understood. The model is evaluated on two case studies each of which specifically assessed one of the contributors to city/atmosphere CO2 exchanges that is weather-sensitive: the buildings on the Toulouse site (France), and the vegetation on the Kumpula site (Finland). These two sites demonstrate the model's ability to reproduce CO2 exchanges between urban surfaces and the atmosphere as well as their daily and seasonal cycles. The Toulouse site underlines the importance of a detailed knowledge of the inhabitants' energy behaviour in order to simulate the CO2 emissions of buildings. Kumpula site demonstrates the ability of the ISBA model, designed to describe the interactions between non-urban vegetation and the atmosphere, to describe the CO2 exchanges between urban vegetation and the atmosphere. The model, thus validated, is used to carry our simulations of CO2 emissions from buildings on the scale of the entire urban agglomeration of Toulouse. These simulations once again highlighted the necessity of a good knowledge of the inhabitant's energy behaviors: on our case study (four days in winter), the 2°C reduction of the nigth-time space heating setpoint temperature reduces CO2 emissions by 33%. During these simulations, the transport of CO2 emitted by the city through the atmosphere is also monitored. This shows that, despite a calm wind situation, the CO2 plume created by the city dissipates rapidly (less than a day), limiting the increase in CO2 concentration over the city. Simulations on other cities are neeeded to determine if this result can be generalized. During this thesis, we studied climate/CO2 interactions at the city scale. In the future, it would be interesting to carry out simulations in future climate or in coupled mode with climate models in order to study the feedback between local and global climate/CO2 links
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Fonseca, Fábio Luís Alves da. « Variação diurna do fluxo de CO2 na interface ar-mar do Oceano Atlântico Equatorial ». Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/14/14133/tde-27062013-114814/.
Texte intégralRésumé :
O ciclo diurno do fluxo de CO2 no oceano Atlântico equatorial para o mês de agosto é estimado utilizando um algoritmo de transferência de gases. O algoritmo é baseado na teoria de similaridade de Monin-Obukhov para fluxos turbulentos na interface ar-mar e na física da transferência de CO2 na camada molecular oceânica. O ciclo diurno do fluxo de CO2, obtido na região, caracteriza o oceano Atlântico equatorial, durante o período, como fonte de CO2 para a atmosfera e seus valores estão entre 0,71 e 0,85 mol CO2 m^-2 ano^-1.The diurnal cycle of CO2 is estimated for the month of August on the Atlantic Ocean using a gas transfer algorithm. The algorithm is based on the Monin-Obukhov similarity theory for turbulent transfer at the air-sea interface and the physics of the CO2 transfer at the oceanic molecular layer.
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Carvalho, Felipe Rust de. « Fluxo de CO2 e CH4 em uma lagoa tropical (Pantanal, Brasil) com gradiente de turbidez ». Universidade Federal de Juiz de Fora, 2015. https://repositorio.ufjf.br/jspui/handle/ufjf/413.
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Ecossistemas de água doce (rios, lagos e reservatórios) desempenham um papel essencial na ciclagem de carbono nos continentes. Esses ambientes são fontes significantes de gases de efeito estufa (GEE) para a atmosfera, principalmente de gás carbônico (CO2) e metano (CH4). Apesar do aumento do número de estimativas, a dinâmica e o controle das emissões naturais de GEE em ambientes aquáticos ainda é pouco estudada, especialmente nos trópicos. O objetivo geral da dissertação foi estimar os fluxos de CO2 e CH4 em uma lagoa tropical rasa com gradiente de turbidez. O trabalho foi realizado na lagoa Sinhá Mariana (MT), uma lagoa pantaneira com a ocorrência de duas regiões hidrológicas distintas; a lagoa é ligada ao rio Mutum de águas claras, pobre em material em suspensão, e baixa turbidez e ao rio Cuiabá de águas túrbidas, que apresenta alta taxa de material em suspensão. Duas coletas foram realizadas no ambiente, caracterizando os períodos hidrológicos de águas altas e águas baixas. A variação temporal, espacial e o pulso de inundação mostraram serem fatores importantes no fluxo de CO2, que variou de -4,95 mmol m-2 d-1 a 282 mmol m-2 d-1 nos períodos amostrados e diferenças significativas foram observadas entre um período e outro, com maiores emissões no período de águas altas (142 ± 40 mmol m-2 d-1) e menores nas águas baixas (2,3 ± 11,5 mmol m-2 d-1). Além disso, os fluxos de CO2 foram significantemente m/aiores nas proximidades do rio Mutum e menores na região túrbida e intermediária da lagoa, em ambos os períodos. Diferentemente, o fluxo total de CH4, embora estimado apenas nas águas altas, registrou os maiores valores médios na região de maior turbidez da lagoa (10,9 ± 6,9 mmol m-2 d-1), seguido pela região intermediária (5,1 ± 3,9 mmol m-2 d-1) e pela região influenciada pela água clara (2,5 ± 1,4 mmol m-2 d-1). A ebulição foi o principal processo de emissão de CH4, responsável por 78% do fluxo total. O gradiente de turbidez registrado ao longo da lagoa pareceu ter sido um fator determinante na dinâmica do fluxo tanto de CO2 quanto do CH4. Os dados deste trabalho reforçam a necessidade da amostragem espacial dos fluxos de CH4 e CO2 em lagos tropical, além de reforçar que estes fluxos podem ser controlados principalmente pela turbidez e pelo pulso de inundação (CO2).
Freshwater ecosystems (lakes, rivers and reservoirs) play an essential role in carbon cycling in the continents. These environments are significant sources of greenhouse gases (GHG), especially carbon dioxide (CO2) and methane (CH4), to the atmosphere. Despite the increase in the number of estimates, the natural GHG emissions dynamics in aquatic environments is still poorly studied, especially in the tropics. The general aim of this work was to estimate the CO2 and CH4 fluxes in a shallow tropical lake with turbidity gradient. The work was conducted in the Sinhá Mariana lake (MT), a wetland lake with the occurrence of two distinct hydrological regions; the lake is connected to the Mutum river (clear water), poor in suspended material with low turbidity, and connected to the Cuiabá River (turbid waters), which features high rate of suspension material. Samples were taken for characterizing the hydrological periods of high and low water. The temporal, spatial variation and the flood pulse shoed to be important factors affecting the CO2 flux, which ranged from -4.95 mmol m-2 d-1 to 282 mmol m-2 d-1. Significant differences were observed from one period to another, with higher emissions during high waters (142 ± 40 mmol m-2 d-1) and lower in the low water (2.3 ± 11.5 mmol m-2 d-1). In addition, the CO2 flux was significantly higher near the Mutum river and lower in the turbid region, in both periods. The total CH4 flux, although estimated only in high waters, showed the highest mean rates in the higher turbidity region of the lake (10.9 ± 6.9 mmol m-2 d-1), followed by the intermediate region (5.1 ± 3.9 mmol m-2 d-1) and the area influenced by clear water (2.5 ± 1.4 mmol m-2 d-1). The ebullition flux was the main CH4 emission pathway, responsible for 78% of the total flux. The turbidity gradient observed along the lake appeared to have been a determining factor in the flux dynamics of both CO2 and CH4. This study data reinforce the need for spatial sampling of CH4 and CO2 fluxes in tropical lakes, in addition to reinforcing that these fluxes can be controlled by turbidity and by the flood pulse (CO2).
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Boiron, Olivier. « Caractérisation aérothermique d'un laser CO2 de puissance à flux axial rapide ». Aix-Marseille 2, 1992. http://www.theses.fr/1992AIX22093.
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Le fonctionnement des lasers continus a gaz requiert un procede de refroidissement d'une grande efficacite pour evacuer l'energie deposee par effet joule dans le milieu amplificateur. Les lasers a flux axial rapide utilisent a cet effet un transport du milieu gazeux permettant son refroidissement par des echangeurs thermiques dans les systemes a circuit ferme. Les proprietes intrinseques de cet ecoulement, turbulence et compressibilite notamment, induisent sur la decharge electrique et sur le depot d'energie dans le gaz, des phenomenes qu'il convient de mieux apprehender afin d'optimiser le rendement et le dimensionnement de ce type de laser. Cette etude a eu pour objet d'etudier experimentalement les proprietes aerothermiques du milieu amplificateur s'ecoulant dans un tube a decharge d'un laser co2 continu, a flux axial turbulent. Les techniques de mesures mises en place a cet effet, anemometrie laser a effet doppler et thermometrie par fluorescence induite, ont permis de mettre en evidence le recollement tres rapide de l'ecoulement a l'aval du dispositif d'injection et de quantifier plus precisement l'evolution du depot d'energie dans le gaz, le long du tube a decharge
Livres sur le sujet "CO2 fluxe"
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Fagnocchi, Giuseppe. Lineamenti di storia della letteratura flautistica : Con un sommario di storia dello strumento. Faenza : Mobydick, 1999.
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Fagnocchi, Giuseppe. Lineamenti di storia della letteratura flautistica : Con un sommario di storia dello strumento. Faenza [Ravenna] : Mobydick, 1999.
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Sugimoto, Hiroyuki. A method forestimating the sea-air CO2 flux in the Pacific Ocean. Tsukuba-shi : Meteorological Research Institute, 2012.
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Koring, Kristina. CO2-Emissionsminderungspotential und technologische Auswirkungen der Oxyfuel-Technologie im Zementklinkerbrennprozess. Düsseldorf : Verlag Bau + Technik GmbH, 2013.
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Oxy-fuel combustion for power generation and carbon dioxide (CO2) capture. Oxford : Woodhead Pub., 2011.
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Savage, Kathleen. BOREAS TGB-1 [i.e. TGB-3] CH4 and CO2 chamber flux data over NSA upland sites. Greenbelt, Md : NASA Goddard Space Flight Center, 2000.
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R, Moore Tim, et Goddard Space Flight Center, dir. BOREAS TGB-1 [i.e. TGB-3] CH4 and CO2 chamber flux data over NSA upland sites. Greenbelt, Md : NASA Goddard Space Flight Center, 2000.
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Savage, Kathleen. BOREAS TGB-1 [i.e. TGB-3] CH4 and CO2 chamber flux data over NSA upland sites. Greenbelt, Md : NASA Goddard Space Flight Center, 2000.
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Meg, Lundstrom, dir. O poder do fluxo : Formas práticas de transformar sua vida com coincidências significativas. Rio de Janeiro : Rocco, 2000.
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United States. National Oceanic and Atmospheric Administration, dir. LONG-TERM STUDIES OF PARTICULATE FLUX ON AND NEAR THE JUAN DE FUCA RIDGE... NOAA TECHNICAL MEMORANDUM OAR PMEL-118... U.S. DEPARTMENT OF COM. [S.l : s.n., 2001.
Trouver le texte intégralChapitres de livres sur le sujet "CO2 fluxe"
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Kürsten, E., et P. Burschel. « Co2-Mitigation By Agroforestry ». Dans Terrestrial Biospheric Carbon Fluxes :, 533–44. Dordrecht : Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1982-5_36.
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Lenz-Wiedemann, Victoria I. S., Tim G. Reichenau, Christian W. Klar et Karl Schneider. « CO2 Fluxes and Transpiration ». Dans Regional Assessment of Global Change Impacts, 287–93. Cham : Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-16751-0_36.
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Overdieck, D. « Effects of Atmospheric CO2 Enrichment on CO2 Exchange Rates of Beech Stands in Small Model Ecosystems ». Dans Terrestrial Biospheric Carbon Fluxes :, 259–77. Dordrecht : Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1982-5_17.
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Akhand, Anirban, Abhra Chanda, Sourav Das, Sugata Hazra et Tomohiro Kuwae. « CO2 Fluxes in Mangrove Ecosystems ». Dans Blue Carbon in Shallow Coastal Ecosystems, 185–221. Singapore : Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-1295-3_7.
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Luxmoore, R. J., S. D. Wullschleger et P. J. Hanson. « Forest Responses to Co2 Enrichment and Climate Warming ». Dans Terrestrial Biospheric Carbon Fluxes :, 309–23. Dordrecht : Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1982-5_20.
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Sauerbeck, D. R. « Co2-Emissions From Agriculture : Sources and Mitigation Potentials ». Dans Terrestrial Biospheric Carbon Fluxes :, 381–88. Dordrecht : Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1982-5_25.
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Orr, James C. « Accord Between Ocean Models Predicting Uptake of Anthropogenic CO2 ». Dans Terrestrial Biospheric Carbon Fluxes :, 465–81. Dordrecht : Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1982-5_32.
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Teskey, Robert O., Mary Anne McGuire, Jasper Bloemen, Doug P. Aubrey et Kathy Steppe. « Respiration and CO2 Fluxes in Trees ». Dans Advances in Photosynthesis and Respiration, 181–207. Cham : Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-68703-2_9.
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Blanke, Michael M. « CO2 Fluctuations and CO2 Fluxes in a Fruit Tree Orchard ». Dans Impacts of Global Change on Tree Physiology and Forest Ecosystems, 173–77. Dordrecht : Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-015-8949-9_23.
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Dale, Virginia H., Sandra Brown, Elizabeth P. Flint, Charles A. S. Hall, Richard A. Houghton, Louis R. Iverson, John F. Richards et James Uhlig. « Estimating CO2 Flux from Tropical Forests ». Dans Effects of Land-Use Change on Atmospheric CO2 Concentrations, 365–78. New York, NY : Springer New York, 1994. http://dx.doi.org/10.1007/978-1-4613-8363-5_9.
Texte intégralActes de conférences sur le sujet "CO2 fluxe"
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Zhao, Yuan, Majid Molki et Michael M. Ohadi. « Heat Transfer and Pressure Drop of CO2 Flow Boiling in Microchannels ». Dans ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1433.
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Abstract An experimental investigation was performed to study the flow boiling heat transfer of CO2 in microchannels. Tests were conducted in a horizontal triangular microchannel with the hydraulic diameter of 0.86 mm. Heat to the test section was provided by direct electrical heating. Experiments were conducted with CO2 at saturation temperatures of 273 to 293 K, mass fluxes of 100 to 820 kg/m2s, heat fluxes of 3 to 23 kW/m2, and qualities of 20% to 85%. It was demonstrated that heat flux had an enhancing effect on the heat transfer coefficient, while mass flux had a negligible effect. Nucleate boiling mechanism is found to be the dominant factor for CO2 flow boiling in microchannels. Heat transfer coefficient degraded quickly at high vapor quality region (0.6–0.7), which is possibly due to flow mal-distribution. Pressure drop increases slightly with vapor quality and/or heat flux. Mass flux has a strong increasing effect on pressure drop.
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Jeong, Siyoung, Eunsang Cho et Hark-koo Kim. « Evaporative Heat Transfer and Pressure Drop of CO2 in a Microchannel Tube ». Dans ASME 3rd International Conference on Microchannels and Minichannels. ASMEDC, 2005. http://dx.doi.org/10.1115/icmm2005-75180.
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Evaporation heat transfer and pressure drop characteristics of carbon dioxide were investigated in a multi-channel micro tube. The aluminum tube has 3 square channels with a hydraulic diameter of 2mm, a wall thickness of 1.5mm, and a length of 5m. The tube was heated directly by electric current. Experiments were conducted at heat fluxes ranging 4–16 kW/m2, mass fluxes from 150 to 750 kg/m2s, evaporative temperature from 0 to 10°C, and qualities from 0 to superheated state. The heat transfer coefficient measured was in the range of 6–15kW/m2K, and the pressure drop was 3–23kPa/m. For the qualities lower than 0.5, the heat transfer coefficient was found to increase with the quality, which is assumed to be the effect of convective boiling. For the qualities higher than 0.6, sudden drop in heat transfer coefficients was sometimes observed due to local dry-out. It was found that dry-out occurred at lower quality if mass flux was smaller. The average heat transfer coefficient was found to increase with increasing heat flux, mass flux, and evaporation temperature, of which the effect of heat flux was the greatest. At given experimental conditions the pressure drop increased almost linearly with increasing quality. The total pressure drop was found to increase with increasing heat flux, mass flux, and evaporation temperature, of which the effect of mass flux was the greatest. From the experimental results simple correlations for heat transfer coefficients and pressure drop were developed.
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Gulev, S. K., S. A. Josey, M. Bourassa, Lars-Anders Breivik, M. F. Cronin, Chris Fairall, Sarah Gille et al. « Surface Energy, CO2 Fluxes and Sea Ice ». Dans OceanObs'09 : Sustained Ocean Observations and Information for Society. European Space Agency, 2010. http://dx.doi.org/10.5270/oceanobs09.pp.19.
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Park, C. Y., et P. S. Hrnjak. « CO2 Flow Boiling Heat Transfer and Flow Pattern at Low Temperatures in Horizontal Smooth Tubes ». Dans ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-15184.
Texte intégralRésumé :
In this study, flow boiling heat transfer coefficients and flow patterns CO2 are examined in horizontal smooth tubes with inner diameter 6.1 and 3.5 mm at low temperatures. In order to measure the heat transfer coefficients, the test tube was heated by two brass pieces maintained a higher temperature than CO2 by a secondary fluid. Flow visualization was carried out at adiabatic conditions. This research was performed at evaporation temperatures of -15 and -30 °C, mass flux from 100 to 400 kg/m2 s, and heat flux from 5 to 15 kW/m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients for the 6.1 and 3.5 mm tubes had nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes. However, enhanced convective boiling contribution was presented for the 3.5 mm tube at 400 kg/m2 s. The presented heat transfer coefficients indicated the reduction of heat transfer coefficient as mass flux increased at low quality regions and also showed that dryout did not occur until the high quality region of 0.8, for mass fluxes of 200 and 400 kg/m2 s. The measured heat transfer coefficients were compared with predicted values with some general correlations to predict flow boiling heat transfer coefficients. The pictures of visualized flow patterns were presented and the flow patterns were compared with a flow pattern map. They were used to explain the relation between the flow boiling heat transfer coefficient and vapor quality at the mass flux of 100 kg/m2 s.
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F. Mazadiego, L., F. Grandia, J. Elio, B. Nissi, O. Vaselli, M. Ortega, J. Caballero, E. Vilanova, E. Chacón et J. Llamas. « Baseline of Soil-Atmosphere CO2 Flux in the Hontomin Site (Burgos, Spain) ». Dans Third EAGE CO2 Geological Storage Workshop. Netherlands : EAGE Publications BV, 2012. http://dx.doi.org/10.3997/2214-4609.20143803.
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Kozlov, Boris, Dmitry Makhan'ko et Mai The Nguyen. « Volume Discharges in CO2-Laser Mixtures at Atmospheric Pressures With High Energy Density ». Dans 2020 7th International Congress on Energy Fluxes and Radiation Effects (EFRE). IEEE, 2020. http://dx.doi.org/10.1109/efre47760.2020.9242065.
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GARCIA, C., C. A. HABERT et C. P. BORGES. « CO2 CAPTURE FROM FLUE GAS USING MEMBRANE CONTACTORS ». Dans XXII Congresso Brasileiro de Engenharia Química. São Paulo : Editora Blucher, 2018. http://dx.doi.org/10.5151/cobeq2018-co.067.
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Jiang, Pei-Xue, Zhi-Hui Li et Chen-Ru Zhao. « Convection Heat Transfer of CO2 at Supercritical Pressures in a Vertical Mini Tube ». Dans ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer. ASMEDC, 2009. http://dx.doi.org/10.1115/mnhmt2009-18343.
Texte intégralRésumé :
This paper presents the experimental and numerical investigation results of the convection heat transfer of CO2 at supercritical pressures in a 0.0992 mm diameter vertical tube at various inlet Reynolds numbers, heat fluxes and flow directions. The effects of buoyancy and flow acceleration resulted from the dramatic properties variation were investigated. Results showed that the local wall temperature varied non-linearly for both upward and downward flow when the heat flux was high. The difference of the local wall temperature between upward flow and downward flow was very small when other test conditions were held the same, which indicates that for supercritical CO2 flowing in a mini tube as employed in this study, the buoyancy effect on the convection heat transfer was quite insignificant, and the flow acceleration induced by the axial density variation with temperature was the main factor that lead to the abnormal local wall temperature distribution at high heat fluxes. The predicted values using the LB low Reynolds number turbulence model correspond well with the measured data. Velocity profiles and turbulence kinetic energy near the wall varying along the tube generated by the numerical simulations were presented to develop a better understanding.
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Zhu, Min, Fangfang Wu, Heng Ma, Shuqun Wu et Chaohai Zhang. « Introduction of Al2O3 Rods into DBD for CO2 Conversion : Understanding the Synergistic Effect of Plasma-Catalysis ». Dans 2020 7th International Congress on Energy Fluxes and Radiation Effects (EFRE). IEEE, 2020. http://dx.doi.org/10.1109/efre47760.2020.9241992.
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Zada, Kyle R., M. Kevin Drost et Brian M. Fronk. « Application of Microscale Devices for Megawatt Scale Concentrating Solar Power Plants ». Dans ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-52529.
Texte intégralRésumé :
Concentrated solar power (CSP) plants have the potential to reduce the consumption of non-renewable resources and greenhouse gas emissions in electricity production. In CSP systems, a field of heliostats focuses solar radiation on a central receiver, which is ultimately transferred to thermal electrical power plant at high temperature. However, the maximum receiver surface fluxes are low (30–100 W cm−2) with high thermal losses, which has limited the market penetration of CSP systems. Recently, small (∼ 4 cm2), laminated micro-channel devices have shown potential to achieve concentrated surface fluxes over 100 W cm−2 using supercritical CO2 as the working fluid. The present study explores the feasibility of using these microscale devices as building blocks for a megawatt scale (250 MW thermal) open solar receiver. This allows for a modular design of the central receiver with non-standard shapes customized to the heliostat field. The results show that the microscale unit-cells have the potential to be scaled to megawatt applications while providing high heat flux and thermal efficiency. At the design incident flux and surface emissivity, a global receiver thermal efficiency of > 90% can be achieved.
Rapports d'organisations sur le sujet "CO2 fluxe"
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Lisa L. Robbins et Kimberly K. Yates. Direct Measurement of CO2 Fluxes in Marine Whitings. Office of Scientific and Technical Information (OSTI), juillet 2001. http://dx.doi.org/10.2172/859282.
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Michael C. Trachtenberg. Biomimetic Membrane for CO2 Capture from Flue Gas. Office of Scientific and Technical Information (OSTI), mai 2007. http://dx.doi.org/10.2172/926669.
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Liang Hu. CO2 Capture from Flue Gas by Phase Transitional Absorption. Office of Scientific and Technical Information (OSTI), juin 2009. http://dx.doi.org/10.2172/975092.
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Tanny, Josef, Gabriel Katul, Shabtai Cohen et Meir Teitel. Application of Turbulent Transport Techniques for Quantifying Whole Canopy Evapotranspiration in Large Agricultural Structures : Measurement and Theory. United States Department of Agriculture, janvier 2011. http://dx.doi.org/10.32747/2011.7592121.bard.
Texte intégralRésumé :
Original objectives and revisions The original objectives of this research, as stated in the approved proposal were: 1. To establish guidelines for the use of turbulent transport techniques as accurate and reliable tool for continuous measurements of whole canopy ET and other scalar fluxes (e.g. heat and CO2) in large agricultural structures. 2. To conduct a detailed experimental study of flow patterns and turbulence characteristics in agricultural structures. 3. To derive theoretical models of air flow and scalar fluxes in agricultural structures that can guide the interpretation of TT measurements for a wide range of conditions. All the objectives have been successfully addressed within the project. The only modification was that the study focused on screenhouses only, while it was originally planned to study large greenhouses as well. This was decided due to the large amount of field and theoretical work required to meet the objectives within screenhouses. Background In agricultural structures such as screenhouses and greenhouses, evapotranspiration (ET) is currently measured using lysimeters or sap flow gauges. These measurements provide ET estimates at the single-plant scale that must then be extrapolated, often statistically or empirically, to the whole canopy for irrigation scheduling purposes. On the other hand, turbulent transport techniques, like the eddy covariance, have become the standard for measuring whole canopy evapotranspiration in the open, but their applicability to agricultural structures has not yet been established. The subject of this project is the application of turbulent transport techniques to estimate ET for irrigation scheduling within large agricultural structures. Major conclusions and achievements The major conclusions of this project are: (i) the eddy covariance technique is suitable for reliable measurements of scalar fluxes (e.g., evapotranspiration, sensible heat, CO2) in most types of large screenhouses under all climatic conditions tested. All studies resulted with fair energy balance closures; (ii) comparison between measurements and theory show that the model is capable in reliably predicting the turbulent flow characteristics and surface fluxes within screenhouses; (iii) flow characteristics within the screenhouse, like flux-variance similarity and turbulence intensity were valid for the application of the eddy covariance technique in screenhouses of relatively dilute screens used for moderate shading and wind breaking. In more dense screens, usually used for insect exclusions, development of turbulent conditions was marginal; (iv) installation of the sensors requires that the system’s footprint will be within the limits of the screenhouse under study, as is the case in the open. A footprint model available in the literature was found to be reliable in assessing the footprint under screenhouse conditions. Implications, both scientific and agricultural The study established for the first time, both experimentally and theoretically, the use of the eddy covariance technique for flux measurements within agricultural screenhouses. Such measurements, along with reliable theoretical models, will enable more accurate assessments of crop water use which may lead to improved crop water management and increased water use efficiency of screenhouse crops.
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Tim Merkel, Karl Amo, Richard Baker, Ramin Daniels, Bilgen Friat, Zhenjie He, Haiqing Lin et Adrian Serbanescu. MEMBRANE PROCESS TO SEQUESTER CO2 FROM POWER PLANT FLUE GAS. Office of Scientific and Technical Information (OSTI), mars 2009. http://dx.doi.org/10.2172/1015458.
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Tsouris, Costas, Gerilynn Moline et Douglas Aaron. Separation of CO2 from Flue Gas and Potential for Geologic Sequestration. Office of Scientific and Technical Information (OSTI), décembre 2022. http://dx.doi.org/10.2172/1902800.
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Fung, Inez. Final report on "Modeling Diurnal Variations of California Land Biosphere CO2 Fluxes". Office of Scientific and Technical Information (OSTI), juillet 2014. http://dx.doi.org/10.2172/1147169.
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Keller, Jason, Scott Bridgham et Qianlai Zhuang. UNDERSTANDING MECHANISTIC CONTROLS OF HETEROTROPHIC CO2 AND CH4 FLUXES IN A PEATLAND WITH DEEP SOIL WARMING AND ATMOSPHERIC CO2 ENRICHMENT. Office of Scientific and Technical Information (OSTI), avril 2021. http://dx.doi.org/10.2172/1778095.
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Andrews, Rodney. SEPARATION OF CO2 FROM FLUE GASES BY CARBON-MULTIWALL CARBON NANOTUBE MEMBRANES. Office of Scientific and Technical Information (OSTI), mars 2001. http://dx.doi.org/10.2172/788129.
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Andrews, Rodney. SEPARATION OF CO2 FROM FLUE GASES BY CARBON-MULTIWALL CARBON NANOTUBE MEMBRANES. Office of Scientific and Technical Information (OSTI), novembre 2001. http://dx.doi.org/10.2172/792162.
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