Density Of Air At Stp Is 0 0013

We study a firn and ice core drilled at the new "Lock-In" site in East Antarctica, located 136 km away from Concordia station towards Durmont d'Urville. High resolution chemical and physical measurements were performed on the core, with a particular focus on the trapping zone of the firn where air bubbles are formed. We measured the air content in the ice, closed and open porous volumes in the firn, firn density, firn liquid conductivity and major ion concentrations, as well as methane concentrations in the ice. The closed and open porosity volumes of firn samples were obtained by the two independent methods of pycnometry and tomography, that yield similar results. The measured increase of the closed porosity with density is used to estimate the air content trapped in the ice with the aid of a simple gas trapping model. Experimental errors have been considered but do not explain the discrepancy between the model and the observations.

The model and data can be reconciled with the introduction of a reduced compression of the closed porosity compared to the open porosity. Yet, it is not clear if this limited compression of closed pores is the actual mechanism responsible for the low amount of air in the ice. High resolution density measurements reveal the presence of a strong layering, manifesting itself as centimeter scale variations. Despite this heterogeneous stratification, all layers, including the ones that are especially dense or less dense compared to their surroundings, display similar pore morphology and closed porosity as function of density. This implies that all layers close in a similar way, even though some close in advance or later compared to the bulk firn. Investigation of the chemistry data suggests that in the trapping zone, the observed stratification is partly related to the presence of chemical impurities.

We study a firn and ice core drilled at the new "Lock-In" site in East Antarctica, located 136 km away from Concordia station towards Dumont d'Urville. High-resolution chemical and physical measurements were performed on the core, with a particular focus on the trapping zone of the firn where air bubbles are formed. We measured the air content in the ice, closed and open porous volumes in the firn, firn density, firn liquid conductivity, major ion concentrations, and methane concentrations in the ice. The closed and open porosity volumes of firn samples were obtained using the two independent methods of pycnometry and tomography, which yield similar results.

The measured increase in the closed porosity with density is used to estimate the air content trapped in the ice with the aid of a simple gas-trapping model. High-resolution density measurements reveal the presence of strong layering, manifesting itself as centimeter-scale variations. Despite this heterogeneous stratification, all layers, including the ones that are especially dense or less dense compared to their surroundings, display similar pore morphology and closed porosity as a function of density. The smoothing is due to the combined effects of diffusive mixing in the firn and the progressive closure of bubbles at the bottom of the firn.

Consequently, the gases trapped in a given ice layer span a distribution of ages. Concentration measurements thus only measure the average value in the ice layer, which removes the fast variability from the record. We focus on the study of East Antarctic plateau ice cores, as these low accumulation ice cores are particularly affected by both layering and smoothing. Our results suggest that the presence of layering artifacts in deep ice cores is linked with the chemical content of the ice. We use high-resolution methane data to parametrize a simple model reproducing the layered gas trapping artifacts for different accumulation conditions typical of the East Antarctic plateau.

We also use the high-resolution methane measurements to estimate the gas age distributions of the enclosed air in the five newly measured ice core sections. It appears that for accumulations below 2 cm ie yr−1 the gas records experience nearly the same degree of smoothing. We therefore propose to use a single gas age distribution to represent the firn smoothing observed in the glacial ice cores of the East Antarctic plateau. Finally, we used the layered gas trapping model and the estimation of glacial firn smoothing to estimate their potential impacts on a million-and-a-half years old ice core from the East Antarctic plateau.

Our results indicate that layering artifacts are no longer individually resolved in the case of very thinned ice near the bedrock. They nonetheless contribute to slight biases of the measured signal (less than 10 ppbv and 0.5 ppmv in the case of methane and carbon dioxide). However, these biases are small compared to the dampening experienced by the record due to firn smoothing.

This means that the gas concentration in an ice layer is the average value over a certain period of time, which removes the fast variability from the record. Here, we focus on the study of East Antarctic Plateau ice cores, as these low-accumulation ice cores are particularly affected by both layering and smoothing. We use high-resolution methane data to test a simple trapping model reproducing the layered gas trapping artifacts for different accumulation conditions typical of the East Antarctic Plateau. It appears that for accumulations below 2 cm ice equivalent yr−1 the gas records experience nearly the same degree of smoothing. We therefore propose to use a single gas age distribution to represent the firn smoothing observed in the glacial ice cores of the East Antarctic Plateau. Finally, we used the layered gas trapping model and the estimation of glacial firn smoothing to quantify their potential impacts on a hypothetical 1.5-million-year-old ice core from the East Antarctic Plateau.

They nonetheless contribute to slight biases of the measured signal (less than 10 ppbv and 0.5 ppmv in the case of methane using our currently established continuous CH4 analysis and carbon dioxide, respectively). Firn, firn density, firn liquid conductivity and major ion concentrations, as well as methane concentrations in the ice. Firn, the interstitial porous network shrinks until it eventually pinches and traps gases in the ice. However, the very process of gas trapping has impacts on the gas signals recorded in ice cores. The interpretation of gas records requires to characterize how ice core and atmospheric signals differ.

The aim of this PhD is to study two effects altering ice core gas records, namely gas layered trapping that creates stratigraphic irregularities and firn smoothing that removes fast variability from the record. A specific focus is put on low-accumulation East Antarctic ice cores.This inquiry starts with the multi-tracer study of a firn core drilled at the Lock-In site, East Antarctica. The results show that the bottom of the firn can be seen as a stack of heterogeneous strata that densify following the same porous network evolution with density. In this vision, the stratification simply reflects the fact that some strata are in advance in their densification, but that pore closure happens in a similar fashion in all strata. This notably means that all strata contain nearly similar amounts of gases, as supported by direct measurements. For this PhD we rely on 6 new high-resolution methane records, measured in several East Antarctic ice cores at IGE.

We show that the abrupt variations are layering artifacts due to stratigraphic irregularities caused by dense firn strata closing in advance. A simple model is developed to simulate the irregular occurrence of layering artifacts.A novel technique is proposed to estimate the age distributions of gases in ice cores, that are responsible for the smoothing of fast atmospheric variations. It can notably be applied to glacial records, and for the first time provides quantitative insights on the smoothing of very low-accumulation records.

Our results show that in East Antarctica, the firn smoothing is weakly sensitive to the accumulation rate, meaning that more information than previously thought is preserved.Finally, we present the development of a new type of micro-mechanical firn model. Its ambition is to simulate the evolution of the porous network of a firn stratum. Such a model could be used to better constrain the enclosure of gases in polar ice under glacial conditions. In order to interpret the paleoclimatic record stored in the air enclosed in polar ice cores, it is crucial to understand the fundamental lock-in process. Within the porous firn, bubbles are sealed continuously until the respective horizontal layer reaches a critical porosity.

Present-day firn air models use a postulated temperature dependence of this value as the only parameter to adjust to the surrounding conditions of individual sites. However, no direct measurements of the firn microstructure could confirm these assumptions. Here we show that the critical porosity is a climate-independent constant by providing an extensive data set of micrometer-resolution 3-D X-ray computer tomographic measurements for ice cores representing different extremes of the temperature and accumulation ranges.

We demonstrate why indirect measurements suggest a climatic dependence and substantiate our observations by applying percolation theory as a theoretical framework for bubble trapping. The incorporation of our results significantly influences the dating of trace gas records, changing gas-age–ice-age differences by up to more than 1000 years. This may further help resolve inconsistencies, such as differences between East Antarctic δ15N records and model results. We expect our findings to be the basis for improved firn air and densification models, leading to lower dating uncertainties. Understanding the slow densification process of polar firn into ice is essential in order to constrain the age difference between the ice matrix and entrapped gases.

The progressive microstructure evolution of the firn column with depth leads to pore closure and gas entrapment. Air transport models in the firn usually include a closed porosity profile based on available data. Pycnometry or melting–refreezing techniques have been used to obtain the ratio of closed to total porosity and air content in closed pores, respectively. X-ray-computed tomography is complementary to these methods, as it enables one to obtain the full pore network in 3-D. This study takes advantage of this nondestructive technique to discuss the morphological evolution of pores on four different Antarctic sites. The computation of refined geometrical parameters for the very cold polar sites Dome C and Lock In provides new information that could be used in further studies.

The comparison of these two sites shows a more tortuous pore network at Lock In than at Dome C, which should result in older gas ages in deep firn at Lock In. A comprehensive estimation of the different errors related to X-ray tomography and to the sample variability has been performed. The procedure described here may be used as a guideline for further experimental characterization of firn samples. We show that the closed-to-total porosity ratio, which is classically used for the detection of pore closure, is strongly affected by the sample size, the image reconstruction, and spatial heterogeneities. In this work, we introduce an alternative parameter, the connectivity index, which is practically independent of sample size and image acquisition conditions, and that accurately predicts the close-off depth and density. Its strength also lies in its simple computation, without any assumption of the pore status .

The close-off prediction is obtained for Dome C and Lock In, without any further numerical simulations on images (e.g., by permeability or diffusivity calculations). Current processes for the capture of CO2 are dependent on amine solutions or chilled ammonia for which the issues of degrading equipment, toxicity, and the high energy cost of amine regeneration are problems (Lu et al., 2015). Inquiries into the gas storage applications of porous materials arose from their low density accompanied by a high internal surface area (Lu and Hao, 2013; Estevez et al., 2018). Inorganic zeolites were the first porous materials to be investigated for the ability to sequester CO2 (Siriwardane et al., 2005; James et al., 2011). Zeolites main attribute however is their use in catalytic cracking of hydrocarbons; an ability that is derived from the high acidity of zeolite frameworks . Compared to COF materials however zeolites will have a smaller pore size and a greater affinity to water, limiting the CO2 capture performance compared to COFs.

Other candidates for mitigating the greenhouse effect via CO2 capture include non-crystalline polymers such as covalent microporous polymers (Dawson et al., 2011a; Sun et al., 2015). CMPs have been used successfully in the fixation of CO2 to epoxides and like COFs can also be co-ordinated to metal atoms (Xiong et al., 2017). CMPs though lack crystallinity making their pore size less uniform than COF materials. Due to the amorphous nature of CMPs there is a lack of precise atomic control of the structure and spacing between the molecular building blocks of the polymer, which is something that has been achieved in COFs (Feng et al., 2012a). Polymeric graphitic carbon nitride (g-C3N4) is promising heterogenous catalyst for the metal-free photocatalytic conversion of CO2 to value added products (Shi et al., 2014; Sun and Liang, 2017). Unlike COFs the porosity of g-C3N4 is derived through the use of templating agents and in bulk application g-C3N4 often suffers low solar light absorption.

COFs are one of the most recently discovered families of porous materials (Dinga and Wang, 2013; Huang et al., 2016; Lohse and Bein, 2018; Zhao F. et al., 2018). COFs are crystalline polymers synthesized from the covalent linkages of building blocks . COF materials can consist of 2D sheets of linked building blocks held together by π-stacking, or also 3D frameworks.

The high porosity and low volumetric density of COFs inspired the thorough investigation into the rational design of COF for CO2 sequestration (Jiang et al., 2019). The pore size of COFs can be varied from small to large by the selection of different sized building blocks. COFs with large pores are better suited for CO2 capture at high pressures wherein the interactions between gas molecules plays a larger role in storage than the interactions between CO2 and the pore walls (Jiang et al., 2019). Meanwhile the chemical makeup of the internal pores in small channeled COFs can be tuned to enhance CO2 affinity thus maximizing the ability for low pressure CO2 adsorption in these materials (Morris and Wheatley, 2008; Li B. et al., 2014). Moreover the porosity of COF materials endows a low density; for instance COF-108, which is a 3D COF, achieved a density of 0.17 g/cm3 which at the time was the lowest density of any COF synthesized (El-Kaderi et al., 2007).

In real firn, the increased pressure in the already closed bubbles might slow their compression compared to open pores. A recent study by Fourteau et al. has shown that reducing the compressibility of closed pores by an amount of 50% in gas trapping models could explain a discrepancy between model results and direct measurements of air content in ice cores. It is however not clear if this reduced compressibility of 50% is physically sound or not.

The results highlight many anomalous layers at the centimeter scale that are unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values that aims at minimizing the bias in the overall signal. Once the layered-trapping-induced anomalies are removed from the record, DO-17 appears to be smoother than its equivalent record from the high-accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation.

However, the degree of smoothing appears surprisingly similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low-accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than previously expected. We also developed a numerical method to extract the gas age distributions in ice layers after the removal of the anomalous layers based on comparison with a weakly smoothed record. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low-temperature and low-accumulation conditions.

We measured the air content in the ice, closed and open porous volumes in the ... Air data provide evidence for presence of modern air entrapped in shallow ice core samples. We propose that this is due to closure of open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios.

Our measurements reveal the presence of open porosity below the depth at which firn air samples can be collected and demonstrate how the composition of bubble air in shallow ice cores can be altered during the post-drilling period through purely physical processes. These results have implications for investigations involving trace gas composition of bubbles in shallow ice cores. Covalent organic frameworks are porous crystalline organic polymers which have been the subject of immense research interest in the past 10 years. COF materials are synthesized by the covalent linkage of organic molecules bonded in a repeating fashion to form a porous crystal that is ideal for gas adsorption and storage. Chemists have strategically designed COFs for the purpose of heterogeneous catalysis of gaseous reactants.

Presented in this critical review are efforts toward developing COFs for the sequestration of CO2 from the atmosphere. Researchers have determined the CO2 adsorption capabilities of several COFs is competitive with the highest surface area materials. Engineering the pore environment of COFs with chemical moieties that interact with CO2 have increased the CO2 adsorption performance. The installation of CO2 binding moieties in the COF has made possible the selective adsorption of CO2 over other gases such as N2.

The high degree of control of internal pore composition in COFs is coupled with high CO2 adsorption to develop heterogeneous catalysts for the conversion of CO2 to value added products. Two notable examples of this catalysis are the fixation of CO2 to epoxides for the synthesis of cyclic carbonates and the reduction of CO2 to CO. Recent examples of COFs for the capture of CO2 will be discussed followed by COF catalysts which use CO2 as a feedstock for the production of value-added products. Progress in the development of CTFs for CO2 fixation continued to 2018 when Yu et al. devised a bottom-up approach entailing deliberate linker selection for the synthesis of function-specific CTFs capable of cycloaddition of CO2 to epoxides (Yu et al., 2018). Using precisely selected polymerization conditions, porous crystalline frameworks CTF-CSU1 and CTF-CSU19 with long-range structure were attained.

To synthesize the CTFs, Yu et al. heated 3,6-dicyano-9H-carbazole and 3,6-dicyano-9-methylcarbazole in ZnCl2 at 400°C for 48 h with the former producing CTF-CSU1 in 93% yield and the latter producing CTF-CSU19 in 91% yield. These CTFs have an exceptionally high nitrogen content due to the presence of both carbazole and triazine moieties. The high nitrogen content of the of extended polymers is known to be beneficial for the capture and catalytic chemical fixation of CO2 (Talapaneni et al., 2015).

Their results showed that in the CO2 cycloaddition, CTF-CSU19 had higher contribution under atmospheric pressure and room temperature (0.1 MPa, 25°C, 48 h) with a TBAB co-catalyst. The elevation in catalytic efficiency was prescribed to the large surface area, pore volume and high nitrogen content. The cycloaddition reaction of CO2 and epoxides having small-sized substituents can be catalyzed using CTF-CSU19 under mild conditions. In addition, CTF-CSU19 can catalyze the fixation of CO2 to epichlorohydrin in high yields although the reacitivty of the larger styrene oxide substrate was more mild .

On the other hand, substrates possessing large substituents like phenyl are relatively slow to react because they cannot easily diffuse into the channels for reactions. The scope of the molecules synthesized by Yu et al. in this study is presented in Table 4. For reusability test, the reaction of epibromohydrin with CO2 catalyzed by CTF-CSUs/TBAB was studied and it was showed that both CTFs can be used for 5 times with only a slight decrease in activity. In 2018 Zhi et al. identified two more COFs, so named COF-JLU6 and COF-JLU7; for the efficient synthesis of cyclic carbonates from CO2 (Zhi et al., 2018). Rather than using a triazine linkage to construct the COF framework Zhi et al. used a triazine-based anilines linked with 2,5-dihydroxyterephaladehyde through imine bonds formed during solvothermal synthesis as depicted in Figure 22. In their study, Zhi et al. used the synthesized imine-linked COFs with hydroxy groups as heterogeneous catalyst for cycloaddition of CO2 into cyclic carbonates under mild conditions.