Critical CO2 Concentration Research Articles

Tracing the Snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics

Abstract. The instability with respect to global glaciation is a fundamental property of the climate system caused by the positive ice-albedo feedback. The atmospheric concentration of carbon dioxide (CO2) at which this Snowball bifurcation occurs changes through Earth's history, most notably because of the slowly increasing solar luminosity. Quantifying this critical CO2 concentration is not only interesting from a climate dynamics perspective but also constitutes an important prerequisite for understanding past Snowball Earth episodes, as well as the conditions for habitability on Earth and other planets. Earlier studies are limited to investigations with very simple climate models for Earth's entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons and the identification of secular changes difficult. Here, we use a coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth's history in one consistent model framework. We find that the critical CO2 concentration decreased more or less logarithmically with increasing solar luminosity until about 1 billion years ago but dropped faster in more recent times. Furthermore, there was a fundamental shift in the dynamics of the critical state about 1.2 billion years ago (unrelated to the downturn in critical CO2 values), driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance: for critical states at low solar luminosities, the ice line lies in the Ferrel cell, stabilised by the poleward winds despite moderate meridional temperature gradients under strong greenhouse warming. For critical states at high solar luminosities, on the other hand, the ice line rests at the Hadley cell boundary, stabilised against the equatorward winds by steep meridional temperature gradients resulting from the increased solar energy input at lower latitudes and stronger Ekman transport in the ocean.

Crystal-Liquid Segregation in Silicocarbonatite Magma Leads to the Formation of Calcite Carbonatite

Abstract A suite of silicocarbonatite and lamprophyre rocks from SW Ireland, with mantle affinity and primitive composition, are used as a proxy for parental carbonated silicate magmas to model early magmatic evolution. Reconstruction of volatile ratios is validated using global occurrences. At 1200°C, the point at which melts transition from ionic liquids with exceptionally low viscosity (0.06 PaS) to covalently polymerised liquid (viscosity up to 1.3 PaS) is 33 mol% SiO2. Incremental and significant increase in magma density accompanies magma ponding, due to dehydration of magmas from model molar CO2/(CO2 + H2O) of 0.60 in plutonic settings to 0.75 for initial subvolcanic magmas. Magma-crystal density differences dictate that repeated influxes of magmas into an inflating magma chamber sustain a mechanical boundary layer between dense (silicate and oxide) mineral layers and a calcite ± phlogopite flotation assemblage. The range of critical CO2 concentration at which calcite floats (10–13 wt% CO2) may be extended by the presence of additional volatiles and fluid bubbles. The model accommodates a range of phenomena observed or inferred for alkaline/carbonatite complexes, including the following: 1, a growing calcite-dominated flotation assemblage with an apparently early magmatic mineralisation; 2, a residual liquid with high concentrations of incompatible metals; 3, variable carbonatite–pyroxenite–phoscorite rock relations; and 4, multiple phases of overprinting metasomatism.

Shock tube evaluation on C2H4 ignition delay differences among N2, Ar, He, CO2 diluent gases

To reveal the fuel ignition delay differences among diluent gases, non-reactive gas Ar, He, N2 and reactive gas CO2 four gases were selected to compare the ethylene ignition delay difference on a shock tube rig. The tested condition temperature and pressure range is 1074–1832 K and 2 atm. Comparison results show that the ethylene ignition delay discrepancy was not pronounced among Ar, He and N2 these non-reactive dilution gases. In terms of CO2 dilution, a critical CO2 concentration was observed. When the CO2 concentration was lower than this critical value, no distinguished ignition delay difference was found. Conversely, the ignition delay difference was pronounced once the CO2 concentration was above this critical value. Particularly, the difference was specially apparent in low temperature conditions. Reaction dynamic analysis shows that the heat effect is predominant in low temperature while the chemical effect is predominant in high temperature in the reaction of CO2 participation. Additionally, the CH* and OH* radical emission signal intensity turns smaller and profile curve turns irregular as the CO2 ratio increases. The CO2 shows a strong inhibition effect which is closely related with H radical consumption reaction CO2+HCO + OH.

Experimental measurement of CO2 diffusion in PMMA and its effect on microcellular foaming

The CO2 diffusion coefficient in polymethyl methacrylate (PMMA) was measured to investigate the relationship between the saturation time and cell nucleation in batch foaming. Measurements were conducted using a visualized high-pressure cell at various temperatures from 303 to 343 K and CO2 pressures of 6, 12, and 18 MPa. The CO2 diffusion coefficient depended strongly on the temperature but weakly on the pressure. Additionally, the CO2 diffusion was promoted by the glass transition behavior of PMMA but was suppressed by the hydrostatic pressure at high pressures.Based on the sorption isotherms of CO2 in PMMA, microcellular PMMA foams were prepared with saturation times from 1800 to 12600 s. Cell nucleation was initiated when the CO2 concentration, which depended upon the CO2 diffusion and saturation time, was sufficient to minimize the energy barrier. Furthermore, the critical CO2 concentration to initiate cell nucleation decreased with an increase in temperature.

Technical insight on the requirements for CO2-saturated growth of microalgae in photobioreactors

Microalgal cultures are usually sparged with CO2-enriched air to preclude CO2 limitation during photoautotrophic growth. However, the CO2 vol% specifically required at operating conditions to meet the carbon requirement of algal cells in photobioreactor is never determined and 1–10% v/v CO2-enriched air is arbitrarily used. A scheme is proposed and experimentally validated for Chlorella vulgaris that allows computing CO2-saturated growth feasible at given CO2 vol% and volumetric O2 mass-transfer coefficient (kLa)O. CO2 sufficiency in an experiment can be theoretically established to adjust conditions for CO2-saturated growth. The methodology completely eliminates the requirement of CO2 electrode for online estimation of dissolved CO2 to determine critical CO2 concentration (Ccrit), specific CO2 uptake rate (SCUR), and volumetric CO2 mass-transfer coefficient (kLa)C required for the governing CO2 mass-transfer equation. Ccrit was estimated from specific O2 production rate (SOPR) measurements at different dissolved CO2 concentrations. SCUR was calculated from SOPR and photosynthetic quotient (PQ) determined from the balanced stoichiometric equation of growth. Effect of light attenuation and nutrient depletion on biomass estimate is also discussed. Furthermore, a simple design of photosynthetic activity measurement system was used, which minimizes light attenuation by hanging a low depth (ca. 10 mm) culture over the light source.

Fabrication of High Temperature Polyphenylsulfone Nanofoams Using High Pressure Liquid Carbon Dioxide

In this paper, we describe fabrication of micro- and nano-structured foams in high temperature polyphenylsulfone (PPSU) with a Tgof 219°C using a solid-state carbon dioxide (CO2) foaming process. We have fabricated microcellular foams with cell size in 1–10 μm range, and for the first time, nanocellular foams with cell size in 20–40 nm range. We discovered a critical CO2concentration window 10.5%–11.8%, where a rapid 2–3 orders of increase in cell nucleation density is observed and cell size drops to below 100 nm. Two approaches are demonstrated to create PPSU nanofoams with a cell size of 20–40 nm: increasing saturation pressure to 7 MPa or decreasing saturation temperature to 10°C. Both approaches use high pressure liquid CO2and the CO2concentration in the polymer are above the critical concentration window, which result in the formation of nanocells. At high CO2concentration of 11.8% and 13%, as foaming temperature increases, the nanostructures transition from closed structure to an open porous structure.

Changes of carbon dioxide concentration in soils caused by forestry machine traffic

Abstract Forestry machine traffic causes a number of changes that are not immediately reflected in morphological changes of surface soil. These changes are physical and chemical in nature. The change in subsurface soil CO2 concentration was one of the parameters of interest. The critical CO2 concentration is thought to fluctuate around 0.6%. The primary objective of this paper was to determine the impact of forestry machine traffic on subsurface soil CO2 concentration. We measured CO2 concentration in the areas undisturbed by machinery and in the ruts in skid trails in eight forest stands. The measurements were performed using a Vaisala MI 70 meter. The results confirmed significant differences in gas concentrations between the individual measurement sites. In the ruts of the skid trails, CO2 concentrations fluctuated in a range of 0.5 to 2.81% and significantly exceeded the critical concentration. Moisture content and bulk density had a significant impact on the change in gas concentration beneath the surface, which was confirmed by multivariate analysis of variance that revealed that the values of the coefficient of correlation fluctuated in a range of 0.39 to 0.74.

Crystallization of polylactide during impregnation with liquid CO2

The evolution of the morphology and degree of crystallinity was investigated postmortem in initially amorphous specimens of a commercial poly(dl-lactide) with a relatively low d-lactide content, after different immersion times in liquid CO2 at 10 °C and 5 MPa. Relatively high concentrations of CO2 induced a crystalline phase that remained stable at room temperature after desorption of the CO2, but was distinct from those generally associated with melt crystallization of polylactides (PLA), as demonstrated by transmission electron microscopy and wide-angle X-ray diffraction, consistent with previous observations. Crystallinity developed at the surface of the specimens within relatively short times compared with those necessary for the overall CO2 content to reach saturation, resulting in a well-defined semicrystalline layer, whose thickness increased with immersion time. This behaviour was argued to be consistent with the existence of a well-defined diffusion front, associated with a step-like CO2 concentration gradient that reflected a strong increase in the diffusivity of the CO2 with the local CO2 content. Crystallization led to a reduction in both the rate of CO2 uptake and the CO2 concentration at saturation compared with that observed for a poly(dl-lactide) with a significantly higher d-lactide content and little tendency to crystallize in the presence of liquid CO2. Assuming the CO2 to be concentrated in the amorphous regions of semicrystalline PLA, a simple model for non-linear Fickian diffusion based on data from previous desorption measurements was used to show that diffusion through the semicrystalline surface layer should dominate impregnation kinetics in initially amorphous specimens that undergo rapid crystallization above a certain critical CO2 concentration, consistent with the observed rates of CO2 uptake.

Some thermodynamic and kinetic low-temperature properties of the PC-CO2 system and morphological characteristics of solid-state PC nanofoams produced with liquid CO2

In this paper, we describe a novel process for creating polycarbonate (PC) nanofoams with cells in the range of 20–30 nm that is based on saturating PC in liquid CO2. We investigated the effect of saturation temperature on the solid-state processing of PC foams in the range of −30 °C to 80 °C. Saturation temperature significantly affects the solubility and diffusivity, and the Arrhenius equation can describe the increase of solubility and decrease of diffusivity as the temperature decreases. We observed a drop in ΔHs, the heat of sorption, at the transition from vapor phase to liquid phase, leading to a weaker dependence of solubility on temperature in the liquid CO2. The dissolution of CO2 in PC dramatically reduces its glass transition temperature in proportion to the amount of CO2 absorbed: incorporation of 20.4% CO2 in PC decreased the Tg from 147 °C down to −7.5 °C. We have identified a critical CO2 concentration window between 15.9% and 18.9%, within which cell nucleation density rapidly increases and consequently foamed microstructure changes from microcellular to nanocellular. Nanofoams with cell nucleation densities exceeding 1015 cells/cm3 and void fraction of up to 60% were achieved. The low-temperature route to enhanced cell nucleation opens up new possibilities for creating nanofoams in thermoplastics. The ability to create cells of different length scales in PC provides a unique opportunity to study the effect of cell size on mechanical and other properties of interest over a cell size range that spans several orders of magnitude.

Experimental Study of Asphaltene Precipitation Behavior During Miscible Carbon Dioxide Injection

Many reservoir and production engineers face asphaltene precipitation as a major problem during miscible carbon dioxide flooding projects. Experimental studies regarding asphaltene precipitation are therefore employed to assist in selecting appropriate facilities and proper operation schemes. During this study, a series of high pressure, high temperature experiments are designed and performed to analyze asphaltene precipitation behavior of an Iranian light reservoir crude at reservoir conditions due to natural production and miscible CO2 gas injection. For both sets of experiments, two different temperature levels (including reservoir temperature) are selected to investigate the role of temperature on asphaltene precipitation as well. Results of natural production experiments indicate that the maximum amount of precipitation occurs at reservoir bubble point pressure, while for each specified pressure asphaltene precipitation increases as the temperature is raised for the whole range of pressures. Carbon dioxide injection experiments, however, have terminated in some remarkable findings: for small CO2 concentrations, CO2 behaves as a hindering agent and lowers the amount of precipitation; on the contrary, for higher fractions (values larger than critical CO2 concentration), the injection of CO2 results in more asphaltene precipitation. An increase in temperature during CO2 injection results in (1) the increase of asphaltene precipitation, (2) the shift of the critical CO2 concentration to lower values, and (3) the decrease of the rate of asphaltene precipitation with CO2 concentration.

Innovative IAQ Organic Sensor

An innovative organic sensor for the monitoring of indoor air quality is described. For office buildings and schools the main requirements are: temperature, RH %, O2 and CO2 concentrations. Moreover low O2 and high CO2 concentrations can be hazardous. There are a lot of sensors based on different principal transducers that are able to detect very low concentrations of CO2, O2, and RH%.The system is based on a resistive interdigital sensor based on an organic sensing material, anthocyanin. Anthocyanins are natural pigments widely distributed in nature: they are produced by plants as secondary metabolites responsible for the pigmentation of many flowers, fruits and vegetables. In this work authors show the possibility to use this innovative organic sensor to monitor indoor air quality by measuring O2 concentration shifts with respect to a standard of 20% (20.000ppm) and the critical CO2 concentration value of about 5% (5000ppm) which is comparable with OSHA (Occupational Safety & Health Administration) standard in an eight-hour time-weighted average (TWA).

Popper, panic and the Perhapsatron: arguments for small science

It is difficult to improve upon Karl Popper’s description of the pace and difficulty of technological progress, and its twin dependence on invention and discovery, when he said (Bondi 1992): ‘We advance like a person walking through a swamp, first painfully on one leg and advancing it, and then on the other. One leg is labelled ‘technology’ and the other ‘science’’. Popper’s words came to mind (with several other thoughts!) when, in the space of a few days, I read about the difficulties in international efforts to develop fusion energy generation (Brumfiel 2008a; Clery 2008a, 2008b; Editorial 2008), a call from a UK academic funding agency for suggested long-term (20–40 years) challenges (EPSRC 2008) and an article that appeared in the UK newspaper, The Guardian, on 1 August, (Simms 2008a) with the headline ‘The final countdown’. The Guardian article was promoted with the apocalyptic message that we have just ‘100 months to save the world’. The ‘100 months’ is the time the authors, a ‘group of global warming experts’, suggest it will take for the carbon dioxide content of the atmosphere [actually, CO2e, a calculated carbon dioxide equivalent (Simms 2008b)] to reach the ‘tipping point’, beyond which ‘potentially’ irreversible changes will occur in the climate system. I am not a climate scientist or even a global warming expert (with or without inverted commas). However, I wonder what the contributors to the 4th Assessment Report of the Intergovernmental Panel on Climate Change, whose data are the basis of the calculation, make of the precision of this estimate and the failure to provide measures of the associated uncertainty. Nor is there any discussion of the different probabilities of irreversible effects arising from exceeding the critical CO2 concentration for 5, 50 or 500 years, before bringing it back below this level. For a better argued pair of (different!) perspectives on the climate change debate, the reader could do much worse than read James Lovelock’s polemic, ‘Revenge of Gaia’ (Lovelock 2006) and Bjorn Lomborg’s ‘Cool It’ (Lomborg 2007). The Guardian article is typical of those that use science to underpin scary scenarios about climate change to catch public attention. From a reading of the 431 subsequent comments on the Guardian website (Guardian 2008) few minds have been changed. Indeed, the 100 month estimate seems to have been received with derision in some quarters and could deflect attention away from the more serious points the authors seek to make. The authors, from the New Economics Foundation, suggest that resource use should be cut, by ‘re-engineering’ the UK economy along the austerity and command lines of the Second World War. They believe that the UK government should unilaterally set an example by not permitting the building of the third runway at London’s Heathrow airport nor the new coal-fired power station in the county of Kent. They also believe that developing countries would then follow this example. Perhaps significantly, the article failed to make any mention at all of the availability of a developed, effective and readily deployable alternative technology, namely nuclear fission, that might aid the controlling of anthropogenic CO2 emissions as part of the transition to more sustainable energy-generating technologies. Nor, following the logic of the 100 month argument, was there any call to divert funding away from fusion research, whose development into a workable and deployed technology is only likely to appear in 3–400 months, if then, long after the supposed ‘tipping point’. This set me thinking about the N. Winterton (&) Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK e-mail: N.Winterton@liverpool.ac.uk

The induction of inorganic carbon transport and external carbonic anhydrase in Chlamydomonas reinhardtii is regulated by external CO2 concentration

ABSTRACTInduction of the carbon concentrating mechanism (CCM) has been investigated during the acclimation of 5% CO2‐grown Chlamydomonas reinhardtii 2137 mt + cells to well‐defined dissolved inorganic carbon (Ci) limited conditions. The CCM components investigated were active HCO3− transport, active CO2 transport and extracellular carbonic anhydrase (CAext) activity. The CAext activity increased 10‐fold within 6 h of acclimation to 0·035% CO2 and there was a further slight increase over the next 18 h. The CAext activity also increased substantially after an 8 h lag period during acclimation to air in darkness. Active CO2 and HCO3− uptake by C. reinhardtii cells were induced within 2 h of acclimation to air, but active CO2 transport was induced prior to active HCO3− transport. Similar results were obtained during acclimation to air in darkness. The critical Ci concentrations effecting the induction of active Ci transport and CAext activity were determined by allowing cells to acclimate to various inflow CO2 concentrations in the range 0·035–0·84% at constant pH. The total Ci concentration eliciting the induction and repression of active Ci transport was higher during acclimation at pH 7·5 than at pH 5·5, but the external CO2 concentration was the same at both pHs of acclimation. The concentration of external CO2 required for the full induction and repression of Ci transport and CAext activity were 10 and 100 μM, respectively. The induction of CAext and active Ci transport are not correlated temporally, but are regulated by the same critical CO2 concentration in the medium.

Effect of CO2 concentration on C:N:P ratio in marine phytoplankton: A species comparison

The effect of variable concentrations of dissolved molecular carbon dioxide, [CO2,aq], on C:N:P ratios in marine phytoplankton was studied in batch cultures under high light, nutrient‐replete conditions at different irradiance cycles. The elemental composition in six out of seven species tested was affected by variation in [CO2,aq]. Among these species, the magnitude of change in C:N:P was similar over the experimental CO2 range. Differences in both cell size and day length‐dependent growth rate had little effect on the critical CO2 concentration below which a further decrease in [CO2,aq] led to large changes in C:N:P ratios. Significant CO2‐related changes in elemental ratios were observed at [CO2,aq] ≪ 10 μmol kg-1 and correlated with a CO2‐dependent decrease in growth rate. At [CO2,aq] typical for ocean surface waters, variation in C:N:P was relatively small under our experimental conditions. No general pattern for CO2‐related changes in the elemental composition could be found with regard to the direction of trends. Either an increase or a decrease in C:N and C:P with increasing [CO2,aq] was observed, depending on the species tested. Diurnal variation in C:N and C:P, tested in Skeletonema costatum, was of a similar magnitude as CO2‐related variation. In this species, the CO2 effect was superimposed on diurnal variation, indicating that differences in elemental ratios at the end of the photoperiod were not caused by a transient buildup of carbon‐rich storage compounds due to a more rapid accumulation of carbohydrates at high CO2 concentrations. If our results obtained under high light, nutrient‐replete conditions are representative for natural phytoplankton populations, CO2‐related changes in plankton stoichiometry are unlikely to have a significant effect on the oceanic carbon cycle.

Induction of CO2 and Bicarbonate Transport in the Green Alga Chlorella ellipsoidea (II. Evidence for Induction in Response to External CO2 Concentration).

The critical species and concentrations of dissolved inorganic carbon (DIC) required for the induction of DIC transport during adaptation to low CO2 were determined for the green alga Chlorella ellipsoidea. The concentration of dissolved CO2 needed for the induction of both CO2 and HCO3- transport was independent of pH during adaptation, whereas the total DIC concentration required increased at alkaline pH. At pH 7.5, the minimum equilibrium DIC concentration at which high CO2 characteristics were maintained, i.e. transport was repressed, was 2100 [mu]M, whereas the maximum equilibrium DIC concentration below which DIC transport was fully induced (DICIND) was 500 [mu]M. Intracellular DIC concentration during adaptation to DICIND decreased temporarily after 2 h to 60% of the maximum level but recovered after 3 h of adaptation. After 3 h of adaptation to DICIND, cells exhibited maximum O2 evolution rate at DICIND. When cells partially adapted to DICIND were returned to high CO2, there was an immediate halt to the induction of transport and a gradual decrease in transport capacity over 23 h. The capacity for the induction of transport was unaffected by the absence of light. These results indicate that changes in the internal DIC pool during adaptation to low CO2 do not trigger the induction of DIC transport and that the induction is not light dependent. Induction of DIC transport in C. ellipsoidea appears to occur in response to the continuous exposure of cells to a critical CO2 concentration in the external medium.

The effects of O2 on net photosynthesis at low temperature (5°C)

Abstract. It has been shown that atmospheric O2 can either depress or stimulate the rate of apparent photosynthesis of white mustard depending on the environmental conditions: CO2 concentration, light intensity and temperature. Stimulation by O2 was observed only under high photon fluence rate and at high CO2 concentrations. The critical CO2 concentration below which O2 was inhibiting and above which it was stimulating was dependent on the temperature of the assay: for plants grown at 12°C the critical CO2 concentration was 13.35 mmol at 5° C and 21.92 mmol at 10° C. Stimulation by O2 depended also on the growth temperature: for measurements at 26.31 mmol m−3 CO2, O2 was stimulating at temperatures less than 12°C for plants grown at 12°C and less than 19°C for plants grown at 27°C. The efficiency of the O2‐dependent stimulation of net photosynthesis was maximum at 9.21 mol m−3 O2 at 26.31 mmol m−3 CO2.Oxygen‐stimulation of net photosynthesis was detected in Nicotiana tabacum L. var Samsun, Lycopersicum esculentum L. and Chenopodium album L. At 5°C and under high photon fluence rate, O2 increased the carboxylation capacity of the photosynthetic apparatus of mustard and decreased its affinity for CO2. The O2 inhibition of the net CO2 uptake observed at low CO2 concentrations was the result of a decrease in the affinity for carbon dioxide. The nature of the mechanism which causes the stimulation of photosynthesis is discussed.

CO2 Transport and photosynthetic productivity of a continuous culture of algae

AbstractThe photosynthetic activity of a continuous culture of the microalga Chlorella vulgaris as it is influenced by the CO2 concentration in the aerating air at different light levels is discussed. It is shown that the characteristic of this behavior is mainly determined by the CO2 transport from the air to the algal cell. Therefore the critical CO2 concentration necessary for optimal growth of a particular alga cannot be given in general, as it differs over a very wide range depending on the dispersion system used in the culture vessel. By analyzing experimental data by means of a mathematical model the overall transport coefficient in a well stirred system for the CO2 transport from the air bubble to the algal cell and the “actual” CO2 kinetics, can be calculated within reasonable limits of accuracy.