Saturated Vapor Research Articles

Study on the Separation of M-Xdi Products by Non-Phosgene Pyrolysis System

m-Xylylene diisocyanate (m-XDI) is a raw material wildly used in the manufacture of high value-added polyurethane products and others. m-XDI is a heat-sensitive and easily polymerized substance, and obtaining high-purity m-XDI in industry is challenging, difficult and costly. In this paper, a coupling process of crystallization distillation was proposed to meet the challenge. First, an experiment was carried out to produce a simulated liquid close to the actual pyrolysis liquid components by the reaction of XDI and ethanol. Secondly, two key factors, the final crystallization temperature and the concentration of the m-XDI reaction liquid, which have great effect on the crystallization process of the m-XDI reaction liquid, are studied. Combined with m-XDI saturated vapor pressure and m-XDI-TLB VLE data, the process of m-XDI separation by crystallization distillation coupling was simulated (as shown in the Figure 1), and the process was compared with that of m-XDI separation by distillation alone. The purity of 99.1% m-XDI was obtained by the coupled process of crystal distillation.

High Rate and Low-Temperature Stable Lithium Metal Batteries Enabled by Lithiophilic 3D Cu-CuSn Porous Framework.

Lithium (Li) metal is regarded as the "Holy Grail" of anodes for high-energy rechargeable lithium batteries by virtue of its ultrahigh theoretical specific capacity and the lowest redox potential. However, the Li dendrite impedes the practical application of Li metal anodes. Herein, lithiophilic three-dimensional Cu-CuSn porous framework (3D Cu-CuSn) was fabricated by a vapor phase dealloying strategy via the difference in saturated vapor pressure between different metals and the Kirkendall effect. CuSn alloy sites were converted into LiSn alloy sites through the molten Li infusion method, and composite Li metal anodes (3D Cu-LiSn-Li) are achieved. Alloyed tin, as the bridge between the porous copper substrate and metallic Li, plays a critical role in optimizing Li nucleation and enhancing the fast lithium migration kinetics. This work demonstrates that lithiophilic binary copper alloys are an effective way to achieve room-temperature high rate performance and satisfied low-temperature cycling stability for Li metal batteries.

Sorption of vapors in methanol soaked and in thermally annealed Matrimid® films

AbstractMatrimid® shows well separated sub‐glass transitions and substantial entrapment of dichloromethane (DCM) in the solution‐cast films. The entrapped DCM was removed by soaking the polymer in the excess of liquid methanol followed either by thermal annealing (vacuum at 200°C) or by the desorption at mild conditions. These physical treatments influenced the sorption kinetics and even the sorption isotherms for vapors of DCM, methanol (MeOH) and acetonitrile (MeCN) at 35.0°C. The sorption isotherms for the thermally annealed Matrimid® were shifted to those for the methanol‐soaked Matrimid® upon its exposure to sufficiently saturated vapors. The physical treatments changed the β sub‐glass transition of the polymer, and did not cause changes in the chemical composition and microstructure as sensed using ATR‐FTIR and SEM, respectively. Relaxation of the annealed Matrimid® was achieved by its soaking in liquid MeOH and by the exposure to vapors, their threshold saturation followed the same order as diffusivity: MeOH > MeCN > DCM. Although methanol appears the least effective agent to induce the relaxation of Matrimid®, it diffuses in and desorbs from the polymer readily. Liquid MeOH and its vapor thus appear the media of choice for causing the relaxation and removal of entrapped solvents from Matrimid®.

Carbon Deposition Mechanisms on Ni-Based Anode for SOFC: A Comparison Between Non-Discharge and Discharge Modes

The nickel/yttria-stabilized zirconia (Ni/YSZ) and nickel/scandia-stabilized zirconia (Ni/ScSZ) have widely used as an anode for solid fuel cells (SOFCs). When hydrocarbon gas is supplied to the Ni-based fuel electrode of SOFCs, carbon is deposited on the anode, and it causes anode destruction. Therefore, carbon deposition control is required.The purpose of this study is to clarify carbon deposition mechanisms to understand how the carbon resistance appears on the Ni-based electrode in non-discharge and discharge modes. NiO/8XSZ powder with a binder was uniaxially pressed to form 0.7mm thick pellet (Ni : XSZ=50:50 vol%, X(dopant)=Y, Sc) which were subsequently sintered. After a reduction in H2 atmosphere, Ni/8XSZ sintered cells were heated in CH4/Ar (S/C ratio (Steam to Carbon) =0, CH4/Ar=0.25) and CH4/H2O/Ar atmosphere (S/C ratio=0.15, CH4/Ar=0.25) using a thermobalance, and the carbon deposition rates were measured from the weight change of the cell at 1173 K and 973 K. In this experiment, the S/C ratio was adjusted by bubbling CH4/Ar gas to set the saturated water vapor pressure at a given temperature. In addition, a power generation experiment of SOFC was conducted at 1073 K to investigate the effect of electrochemical reactions on the carbon deposition. The SOFC cells were prepared as follows. YSZ suspension was spin-coated on the NiO/8YSZ substrate. The electrolyte/electrode bilayer was co-sintered at 1673K. Then, a paste of LSM/YSZ was coated on electrolyte and sintered at 1473K. The cell was sealed to the alumina tube in the electric furnace. The anode side was fed with CH4/Ar/H2O (S/C ratio = 0.15) and the cathode side was exposed to O2. Current density was set to 126mA/cm2 for 30 min. After discharge, the anode surface was observed using SEM/EDS.As a result, the carbon deposition rate of Ni/ScSZ was lower than that of Ni/YSZ by 34 % at 1173 K and S/C=0 under non-discharge mode. This result indicated that the Ni/ScSZ exhibited superior carbon deposition tolerance than the Ni/YSZ at 1173 K. Steam reforming reaction was also different between the Ni/YSZ and Ni/ScSZ. Previous studies showed that carbon deposition tended to progress easily at the metal/solid electrolyte interface. The difference in carbon deposition behavior between Ni/YSZ and Ni/ScSZ was caused by the difference in the interface structure. On the other hand, the carbon deposition rate of Ni/ScSZ was higher than that of Ni/YSZ at 973 K which was opposite to that at 1173 K. Moreover, the rate of carbon reforming reaction (C+H2O→CO+H2) of Ni/YSZ was higher than that of Ni/ScSZ. In fact, the Ni/YSZ anode showed superior carbon tolerance than the Ni/ScSZ at lower temperature. XRD (X-ray Diffraction) analysis showed that the ScSZ with cubic structure was partially changed to the rhombohedral structure after the carbon deposition at high temperature while YSZ cubic structure was unchanged. This implied that the rhombohedral structure at the interface inhibited the carbon deposition reaction, suggesting that the electrolyte structure influenced the carbon deposition and steam reforming reactions. Therefore, it was shown that the electrolyte structure can control the carbon deposition while the same Ni was used. These findings give an useful hint to design the carbon tolerance electrode.Meanwhile, carbon deposition was not found on the Ni/YSZ surface after discharge at 1073 K. This indicated O2- ion improved the carbon tolerance during discharge. Comparison of carbon deposition between Ni/YSZ and Ni/ScSZ will be discussed using DFT (Density Functional Calculation).

Molecular Structure of Gaseous Oxopivalate Co(II): Electronic States of Various Multiplicities.

Synchronous electron diffraction/mass spectrometry was used to study the composition and structure of molecular forms existing in a saturated vapor of cobalt(II) oxopivalate at T = 410 K. It was found that monomeric complexes Co4O(piv)6 dominate in the vapor. The complex geometry possesses the C3 symmetry with bond lengths Co-Oc = 1.975(5) Å and Co-O = 1.963(5) Å, as well as bond angles Oc-Co-O = 111.8(3)°, Co-Oc-Co = 110.4(6)°, O-Co-O = 107.1(3)° in the central OcCo4 fragment and four OcCoO3 fragments. The presence of an open 3d shell for each Co atom leads to the possibility of the existence of electronic states of the Co4O(piv)6 complex with Multiplicities 1, 3, 5, 7, 9, 11, and 13. For them, the CASSCF and XMCQDPT2 calculations predict similar energies, identical shapes of active orbitals, and geometric parameters, the difference between which is comparable with the error of determination by the electron diffraction experiment. QTAIM and NBO analysis show that the Co-Oc and Co-O bonds can be attributed to ionic (or coordination) bonds with a significant contribution of the covalent component. The high volatility and simple vapor composition make it possible to recommend cobalt (II) oxopivalate as precursors in the preparation of oxide films or coatings in the CVD technologies. The features of the electronic and geometric structure of the Co4O(piv)6 complex allows for the conclude that only a very small change in energy is required for the transition from antiferromagnetically to ferromagnetically coupled Co atoms.

Behavior of IMERG precipitation extremes with temperature at different spatial resolution

The Clausius-Clapeyron equation determines how saturation vapor pressure increases with temperature, which is important in determining variations in extreme precipitation. Regionally, the scaling of C–C does not vary significantly, but the relationship with extreme precipitation does. In this study, the precipitation from Integrated Multisatellite Retrievals for Global Precipitation Measurement (IMERG) is tested for its accuracy in scaling extreme precipitation rates with temperature (termed scaling factor). We utilized the IMERG precipitation data across the Indian Sub-continent at 0.1° × 0.1°, 0.25° × 0.25° and 0.5° × 0.5° spatial resolution from 2001 to 2020 datasets. Our findings show that, there is a transition in Global Precipitation Measurement’s precipitation extremes estimations (95th percentile) around 30 °C over spatial resolution of 0.25° and 0.1° from C–C to sub C–C. This study also evaluates the sensitivity of C–C scaling in different regimes of India having homogeneous precipitation climatology. It is found that southeast India is highly sensitive to the spatial resolution, as it shows steep slopes in extreme precipitation rates at high dew point temperatures. This is the first study to evaluate the sensitivity of spatial resolution on C–C analysis as most of the previous studies have considered temporal variations.

Thermodynamic analysis of nifedipine sublimation, dissolution and solvation

The saturated vapour pressure of the cardiovascular drug nifedipine is measured within the temperature range (390.15–404.15) K by the inert gas-carrier method. The thermodynamic functions of sublimation of the compounds are calculated at a reference temperature. The standard molar enthalpy of nifedipine sublimation is found to be equal to 144.8 kJ∙mol−1. The drug solubility in solvents modeling various media of the human body is determined in the temperature range (293.15–313.15) K. In the ascending order of solubility values of the studied compound, the solvents can be arranged as follows: buffer pH 7.4, buffer pH 2.0, n-hexane, 1-octanol. The solute–solvent intermolecular interactions are discussed based on the thermodynamic functions of solubility, solvation and transfer.

Breaking through the Thermodynamics “Wilds” of Metal–Organic Chemical Vapor Deposition Precursors: Metal tris-Acetylacetonates

Metal acetylacetonates belong to the β-diketonate family and are considered as classics among precursors for metal–organic chemical vapor deposition (MOCVD). The success of film preparation is crucially dependent on the volatilization thermodynamics of the precursors used. Data on the volatilization thermodynamics of metal acetylacetonates are in huge disarray. We amassed and analyzed experimental data on the vapor pressures and on the enthalpies and entropies of fusion, vaporization, and sublimation of acetylacetonate tris-complexes of metals(III) (Al, Sc, Cr, Mn, Fe, Co, Ru, Rh, In, and Ir) available in the literary sources. In addition, saturated vapor pressures over crystalline Al(III), Cr(III), and In(III) acetylacetonates and corresponding thermodynamic sublimation properties were determined. New findings enabled us to arbitrate the conflict among literature data. The enthalpies and entropies of sublimation, vaporization, and fusion were adjusted to the reference temperature for a correct comparison using the empirically estimated differences in heat capacities. The heat capacity of the crystalline phase was shown to depend weakly on the metal atom. As a result, a reliable set of enthalpies and entropies of the mentioned processes of fundamental importance was derived for ten metal complexes. Relationships between volatility and structure were established depending on the central metal. The suggested algorithm can be fairly easily transferred to the acetylacetonate or other β-diketonate isoligand complexes with metals of different valence.

Study on the Evolution Behavior of Humidity Fields in Cement Concrete Pavements of a Coastal Airport During Early Stages in Humid and Hot Areas.

Airport pavements are prone to early defects during the construction phase, and their early performance during the construction phase is significantly affected by the external temperature field. This article takes the concrete pavement of Xiamen Xiang'an New Airport as an example and uses a three-dimensional (3D) humidity simulation program for cement concrete pavement to study the evolution behavior of the early stage humidity field of the pavement in a humid and hot climate environment. The results indicate that the evolution law of the humidity field of the concrete pavement slab was consistent with the environmental field, presenting a 24 h periodic variation. The environmental field had a significant impact on the humidity of the surface layer of the pavement slab, and the humidity decreased rapidly with time. There was a humidity gradient on both the horizontal plane and the cutting plane of the slab, the horizontal humidity was concentrated from the boundary into the middle of the slab, and the sectional humidity was concentrated from the top to the bottom of the slab. Environmental parameters, construction parameters, and material and structural parameters all influenced humidity through humidity exchange or by changing the saturated vapor pressure inside the slab. The humidity field was most sensitive to environmental humidity and maintenance methods, but less sensitive to material parameters and structural parameters. Through analysis, it is advisable to avoid hot seasons, choose periods of increased environmental humidity, adopt appropriate maintenance methods during construction to reduce humidity stress on the slab, and therefore decrease early stage deterioration and improve service life.

Experimental and computational investigation of thermal performance and fluid flow in two-phase closed thermosyphon

Over the last two decades, energy recovery has become increasingly important in the transition from fossil fuels to green energy. Waste heat recovery, such as the two-phase closed thermosyphon (TPCT) type of heat exchanger, is a highly efficient energy recovery technique. However, accurately predicting the thermal performance and flow patterns in TPCTs is challenging due to the complex physics of phase-change phenomena. A new predictive model is suggested that can provide improved accuracy when predicting thermal performance and flow patterns in TPCTs. An experimental study was conducted to acquire the data, and the results were compared with computational results obtained from the new proposed model. The model uses the volume of fluid (VOF) model with the Lee model for the phase change process in OpenFOAM v2106. To increase accuracy, the saturation temperature and vapor density were defined as a function based on the mass balance in the TPCT. In addition, a simulation was conducted to predict the thermal performance and flow patterns in a TPCT, during which the effects of the empirical value of the mass transfer intensity factor were investigated. The study is expected to provide insights into phase-change modeling with high accuracy and an understanding of the thermal characteristics of TPCTs.

Thermodynamic and kinetic analyses and experimental verification of tellurium and bismuth recovery from bismuth telluride waste by selective sulfidation-vacuum volatilization

The recovery of tellurium and bismuth from bismuth telluride waste is of great significance in improving the utilization levels of renewable resources, protecting the ecological environment and alleviating the problem of resource shortages. In this paper, tellurium and bismuth were recovered from bismuth telluride waste by selective sulfidation–vacuum volatilization. The Gibbs free energy, phase diagram and thermodynamic equilibrium diagram for the core reaction were calculated and analyzed to determine the possible reactions and the conditions required for the stability of bismuth telluride during the sulfidation process. After calculating the saturated vapor pressures, it was concluded that tellurium and bismuth sulfide could be separated by vacuum volatilization. The thermogravimetric analyses and differential scanning calorimetry were then used to analyze the reaction between bismuth telluride and sulfur. The results indicated that the temperature range for the sulfidation reaction should be 491–620 K. The volatilization temperature of tellurium should be greater than 695 K. The evaporation kinetics for tellurium and bismuth sulfide showed that the evaporation rate of tellurium was much higher than that of bismuth sulfide. Furthermore, experiments were conducted to verify the reliability of the theoretical analysis, and these were in good agreement with the thermodynamic and kinetic results. The direct yields of tellurium and bismuth were 99.65% and 99.49%, respectively. These results confirmed that the selective sulfidation-vacuum volatilization method is a feasible alternative for recovery of tellurium and bismuth from bismuth telluride waste.

Condensation Heat Transfer and Pressure Drop of Acoustically Actuated Horizontal Two-Phase Flow

An acoustic actuation technique to enhance condensation inside horizontal tubes is developed and experimentally demonstrated. Heat exchanger headers are used as Helmholtz resonators, allowing low-frequency (∼10 Hz) acoustic waves to propagate and be reflected within the condenser, improving mixing saturated vapor and condensed liquid, thereby enhancing heat transfer. Heat transfer coefficients and pressure drops are measured to evaluate the heat transfer enhancement and pressure drop penalty as a function of vapor quality, mass flux, temperature difference, and acoustic wave amplitude and frequency. Experiments are conducted using a tube-in-tube heat exchanger with an inner diameter of 14.45 mm that partially condenses refrigerant R134a at 950 kPa across vapor qualities ranging from 5% to 80% as mass fluxes of 120 and 180 kg m−2 s−1 and temperature differences of 6 and 12 K. The actuation amplitude and frequency are varied from 0.5 to 6 mm and 2 – 20 Hz, respectively to characterize the acoustic response. Heat transfer enhancement mechanisms are hypothesized and evaluated based on the experimental results, concluding that changes in two-phase flow patterns and increased convective effects lead to significant enhancement at low qualities but negligible enhancement at high qualities when the flow is annular. Existing correlations and modifications to existing models are proposed to explain the observed enhancement, and a simple correlation based on a heat-and-momentum analogy is proposed, which predicts both baseline and enhanced heat transfer data within 2.7%.

Influence of cyclic water content changes during long-term storage on the mechanical stability of wood pellets

In the case of wood pellets, a water content >10 wt.-% should not be exceeded, as they begin to break even under low mechanical loads. However, during storage, they are exposed to different environmental conditions, including rising and falling humidity. In this study, by humidifying and re-drying wood pellets, it was found that their loss of stability at high humidity is reversible and they can recover to a high degree at subsequent low humidity. However, exceeding the saturation vapor pressure and a pellet water content >12 wt.-% leads to much greater swelling and loss of stability. In this case, pellets recover significantly less during subsequent drying. Long-term tests with multiple cycles of humidification <12 wt.-% have shown that pellets with high density and stability in their original state suffer a significant loss of stability within the first 10 cycles, while pellets with high porosity didn't change during long-term storage.

A Multiscale Four-Dimensional Variational Data Assimilation Scheme: A Squall-Line Case Study

Abstract This study presents a multiscale four-dimensional variational data assimilation (MS-4DVar) scheme that aims to assimilate multiscale information from conventional and radar observations. The MS-4DVar scheme separately assimilates conventional and radar data in different outer loop iterations of an incremental 4DVar with varied resolutions in the tangent linear and adjoint models (TLM/ADM) and time window lengths in the 4DVar. The MS-4DVar scheme was evaluated through a series of single observation tests and several cycled assimilation and forecasting experiments for a real squall-line case. Our results indicated that different TLM/ADM resolutions and time window lengths applied to the conventional and radar observations improved the multiscale analysis. In addition, the MS-4DVar scheme was more efficient than the common 4DVar because of the low-resolution TLM/ADM used for conventional data and the shortened time window length for radar data. Verification of the squall-line forecasts suggested that the MS-4DVar scheme improved the hourly accumulated precipitation and radar reflectivity forecast skills and reduced the forecast errors of both large-scale environmental and convective-scale states. Further diagnosis revealed that the improvement of precipitation forecast skill was attributable to the stronger cold pool, deeper saturated water vapor layer, and stronger updraft of the simulated squall-line system, as well as a more favorable convective environment.

Real-time system for monitoring the water vapour concentration and temperature of air exhaled from human lungs

This article describes a fully optoelectronic system for measuring the H2O concentration and temperature of air exhaled from human lungs. A device consisting of both a laser hygrometer and an ultra-fast resistive thermometer. It was tested during an experiment with saturated water vapour, confirming its accuracy for measuring H2O concentration in air. Data, from a preliminary investigation of breath samples from anonymous adult volunteers, is presented.

Biohybrid Technology for the Detection of Ultralow Concentrations of Trinitrotoluene in Air

The technology is based on recording the focal activity (FA) of the olfactory bulb (OB) of rats upon the exposure rats to trinitrotoluene (TNT) vapors in the concentration 4.7 × 10–15 g/cm3, separately and in a mixture with saturated vapors of a complex interference composed of spices. The focal activity of the rat olfactory bulb was recorded using an array of 16 special electrodes implanted in the dorsal part of the rat olfactory bulb. The setup contained a box with a rat, sources of vapors (odorants), a multichannel digital system for recording electrical signals from an electrode array, and software performing algorithms for recognizing and classifying odorants presented to the rat. One source of TNT vapors was a device for batch volumetric preparation with a concentration of about 10–15 g/cm3, and another source was a source with a concentration of 4.7 × 10–15 g/cm3 in an air flow presented to rats. Data from 25 tests showed a 100% probability of detecting TNT vapors of the specified concentrations in pure air and also in the presence of a complex odor interference in the form of vapors from a mixture of red pepper, coriander, tobacco, etc., which, as a rule, mask the smell of TNT for animals.The technology is based on recording the focal activity (FA) of the olfactory bulb (OB) of rats upon the exposure rats to trinitrotoluene (TNT) vapors in the concentration 4.7 × 10–15 g/cm3, separately and in a mixture with saturated vapors of a complex interference composed of spices. The focal activity of the rat olfactory bulb was recorded using an array of 16 special electrodes implanted in the dorsal part of the rat olfactory bulb. The setup contained a box with a rat, sources of vapors (odorants), a multichannel digital system for recording electrical signals from an electrode array, and software performing algorithms for recognizing and classifying odorants presented to the rat. One source of TNT vapors was a device for batch volumetric preparation with a concentration of about 10–15 g/cm3, and another source was a source with a concentration of 4.7 × 10–15 g/cm3 in an air flow presented to rats. Data from 25 tests showed a 100% probability of detecting TNT vapors of the specified concentrations in pure air and also in the presence of a complex odor interference in the form of vapors from a mixture of red pepper, coriander, tobacco, etc., which, as a rule, mask the smell of TNT for animals.

Biohybrid Technology for the Detection of Ultralow Concentrations of Trinitrotoluene in Air

The technology is based on recording the focal activity (FA) of the olfactory bulb (OB) of rats upon the exposure rats to trinitrotoluene (TNT) vapors in the concentration 4.7 × 10–15 g/cm3, separately and in a mixture with saturated vapors of a complex interference composed of spices. The focal activity of the rat olfactory bulb was recorded using an array of 16 special electrodes implanted in the dorsal part of the rat olfactory bulb. The setup contained a box with a rat, sources of vapors (odorants), a multichannel digital system for recording electrical signals from an electrode array, and software performing algorithms for recognizing and classifying odorants presented to the rat. One source of TNT vapors was a device for batch volumetric preparation with a concentration of about 10–15 g/cm3, and another source was a source with a concentration of 4.7 × 10–15 g/cm3 in an air flow presented to rats. Data from 25 tests showed a 100% probability of detecting TNT vapors of the specified concentrations in pure air and also in the presence of a complex odor interference in the form of vapors from a mixture of red pepper, coriander, tobacco, etc., which, as a rule, mask the smell of TNT for animals.

Tert-Butyl Ethers of Renewable Diols as Oxygenate Additives to Automobile Gasolines. Part II: Ethers of Ethylene Glycol and 2,3-Butanediol

The results obtained in the second part of the study of vicinal (tert-butoxy)alkanols as additives to automobile gasolines are presented. Mono-tert-butyl ethers of ethylene glycol (ETBE) and 2,3-butanediol (BTBE) were prepared by direct acid-catalyzed alkylation of the corresponding diols with tert-butanol. The substances obtained were characterized by main physical properties (density, viscosity, boiling point, crystallization point, specific heat of combustion) and were studied as additives to automobile gasolines. The effect of ether additives on the main physicochemical properties of gasolines (fractional composition, saturated vapor pressure, concentration of actual resins, knock resistance), including ethanol-containing gasolines, was studied. The mean research/motor blending octane numbers for ETBE and BTBE were 130/103 and 115/97, respectively. Inclusion of ETBE/BTBE into the formulations of ethanol-containing gasolines allowed the cloud point to be considerably reduced without unambiguous synergistic effect on the knock resistance.

Disentangling day–night contributions toward altering atmospheric desiccation strength for US croplands

AbstractVapor pressure deficit (VPD) is the difference between saturation and actual water vapor pressures and is driven by interactions between air temperature and humidity. Globally, VPD observations indicate drying of the atmosphere, while air temperature (T) and relative humidity (RH) have changed asymmetrically during daytime versus nighttime. However, whether daytime or nighttime T (Tday and Tnight, respectively) and RH (RHday and RHnight, respectively) have been more important to VPD change is unknown, and so is the seasonal variation of this importance. This research determines the relative contribution of Tday, Tnight, RHday, and RHnight to VPD change observed during 1981–2021 across the conterminous United States. Tday contributed 41% to driving a VPD increase of 2.1 standard deviations (SD), followed by contributions of 25%, 22%, and 12% from RHday, RHnight, and Tnight, respectively. Regions with significant VPD increase have seen increase in Tday (by 1 SD) and Tnight (by 0.9 SD) and a decrease in RHday (by 1 SD) and RHnight (by 3.4 SD). Diurnal asymmetry in warming and drying trends was true for most months, with greater rates of change during the nighttime than daytime. Tday was the dominant driver of the annual mean VPD rise for 70% of the counties, followed by RHday (18%), RHnight (11%), and Tnight (1%). We conclude that warming and drying during the days and nights together explain increased VPD across the US croplands and that climate stressors during days and nights should be viewed independently due to their crop‐specific impacts that vary spatially and seasonally.

Moisture-driven CO2 pump for direct air capture

Direct Air Capture, the chemical separation of carbon dioxide (CO2) from air, is considered a necessary approach to generate negative carbon emissions and in turn limit global warming, though energetic and monetary costs must continue to decline to meet the needed gigaton scale. The promise of energy-efficient and continuous carbon dioxide membrane separation has only recently been investigated with the development of facilitated chemical transport and novel electrochemically driven methods. This work demonstrates the potential for continuous pumping of CO2 from air using commercial anion exchange membranes driven solely by a water vapor gradient. A reactive transport model that couples ionic transport with moisture sensitive bicarbonate chemistry in charged polymers, also termed moisture swing sorption, was developed alongside experimentally measured equilibrium and transport properties of CO2 and water vapor in Fumasep FAA-3 to determine the mass transport limits of such a system. The results show that the commercial membrane is kinetically limited by the moisture sensitive chemistry, enabling a CO2 current of 1.1 μmol/m2∙ s. In diffusion limited materials, a CO2 pumping flux can reach 11 μmol/m2∙ s in and peak performance is expected with a dry air relative humidity around 50% pumping into a saturated water vapor permeate. In all configurations, water loss becomes the major cost in such a separation and must be managed through optimal polymer design or water recovery mechanisms. The work demonstrates the applicability of a new driving force, the evaporation of water, to meet the energetic demand of CO2 separation from air.