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CO2 Density (co2 + density)

Distribution by Scientific Domains

Earth and Environmental Science	50%

Selected Abstracts

Large annual net ecosystem CO2 uptake of a Mojave Desert ecosystem

GLOBAL CHANGE BIOLOGY, Issue 7 2008
GEORG WOHLFAHRT
Abstract The net ecosystem CO2 exchange (NEE) between a Mojave Desert ecosystem and the atmosphere was measured over the course of 2 years at the Mojave Global Change Facility (MGCF, Nevada, USA) using the eddy covariance method. The investigated desert ecosystem was a sink for CO2, taking up 102±67 and 110±70 g C m,2 during 2005 and 2006, respectively. A comprehensive uncertainty analysis showed that most of the uncertainty of the inferred sink strength was due to the need to account for the effects of air density fluctuations on CO2 densities measured with an open-path infrared gas analyser. In order to keep this uncertainty within acceptable bounds, highest standards with regard to maintenance of instrumentation and flux measurement postprocessing have to be met. Most of the variability in half-hourly NEE was explained by the amount of incident photosynthetically active radiation (PAR). On a seasonal scale, PAR and soil water content were the most important determinants of NEE. Precipitation events resulted in an initial pulse of CO2 to the atmosphere, temporarily reducing NEE or even causing it to switch sign. During summer, when soil moisture was low, a lag of 3,4 days was observed before the correlation between NEE and precipitation switched from positive to negative, as opposed to conditions of high soil water availability in spring, when this transition occurred within the same day the rain took place. Our results indicate that desert ecosystem CO2 exchange may be playing a much larger role in global carbon cycling and in modulating atmospheric CO2 levels than previously assumed , especially since arid and semiarid biomes make up >30% of Earth's land surface. [source]

Primary carbonate/CO2 inclusions in sapphirine-bearing granulites from central Sri Lanka

JOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2000
Bolder-Schrijver
High-density CO2 -rich fluid inclusions from a sapphirine-bearing granulite (Hakurutale, Sri Lanka) have been studied by microthermometry, Raman spectrometry and SEM analysis. Based on textural evidence, two groups of inclusions can be identified: primary, negative crystal shaped inclusions (group I) and pseudo-secondary inclusions, which experienced a local, limited post-trapping modification (group II). Both groups contain magnesite as a daughter mineral, occurring in a relatively constant fluid/solid inclusion volume ratio (volsolid =0.15 total volume). CO2 densities for group I and II differ only slightly. Both groups contain a fluid, which was initially trapped at peak metamorphic conditions as a homogeneous (CO2+MgCO3) mixture. Thermodynamic calculations suggest that such a fluid (CO2+15 vol% MgCO3) is stable under granulite facies conditions. After trapping, magnesite separated upon cooling, while the remaining CO2 density suffered minor re-adjustments. A model isochore based on the integration of the magnesite molar volume in the CO2 fluid passes about 1.5,2 kbar below peak metamorphic conditions. This remaining discrepancy can be explained by the possible role of a small quantity of additional water. [source]

Supercritical carbon dioxide separation of bergamot essential oil by a countercurrent process

FLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2003
Marco Poiana
Abstract The ef,ciency of separation of bergamot essential oil, performed by a countercurrent column ,lled with Raschig rings and using supercritical carbon dioxide as partition solvent, is affected by various parameters. In the experiments explained in this work, the direct effect of CO2 density was shown and the ratio between the amount of oil loaded to on the column and the amount of CO2 used were discussed. The conditions that produced extracts with a similar volatile fraction composition of starting material and with a high yield (more than 80% of recovery) were those with a low feed:solvent ratio; the lowest bergaptene content was obtained at low CO2 density or at high feed:solvent ratio. A good result was observed at a CO2 density of 206 g/dm3 (8 MPa of pressure and a temperature gradient of 46,50,54 °C) and a feed:solvent ratio of 9.4,9.6; in this separation, a yield of 74,77% and a bergaptene content lower than 0.01% was measured. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Primary carbonate/CO2 inclusions in sapphirine-bearing granulites from central Sri Lanka

CO2 Density-Raman Shift Relation Derived from Synthetic Inclusions in Fused Silica Capillaries and Its Application

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009
Yucai SONG
Abstract: The densities of CO2 inclusions in minerals are commonly used to determine the crystallizing conditions of the host minerals. However, conventional microthermometry is difficult to apply for inclusions of small size (< 5,10 ,m) or low density. Raman analysis is an alternative method for determining CO2 density, provided that the CO2 density,Raman shift relation is known. This study aims to establish this CO2 density,Raman shift relation by using CO2 inclusions synthesized in fused silica capillaries. By using this newly-developed synthetic technique, we formed pure CO2 inclusions, and their densities were determined by microthermometry. The Raman analysis showed that the relation between CO2 density (D in g/cm3) and the separations (? in cm,1) between the two main bands (i.e. Fermi diad bands) in CO2 Raman spectra can be represented by a cubic equation: D (g/cm3)=0.74203(,0.019?3+5.90332?2,610.79472?+21050.30165),3.54278 (r2=0.99920). Our calculated D value for a given ? is between those obtained from two previously-reported equations, which were derived from different experimental methods. An example was given in this study to demonstrate that the densities of natural CO2 inclusions that could not be derived from microthermometry could be determined by using our method. [source]