Role Of Water Vapor Research Articles

The Role of Water Vapor and Temperature in the Thermodynamics of Tropical Northeast Pacific and African Easterly Waves

Abstract The thermodynamic processes associated with convection in tropical African and northeastern Pacific easterly waves (AEWs and PEWs, respectively) are examined on the basis of empirical orthogonal functions (EOFs) and a plume buoyancy framework. Linear regression analysis reveals the relationship between temperature, moisture, buoyancy, and precipitation in EWs. Plume buoyancy is found to be highly correlated with rainfall in both AEWs and PEWs, and a near 1:1 relationship is found between a buoyancy-based diagnostic of rainfall and rainfall rates from ERA5. Close inspection of the contribution of moisture and temperature to plume buoyancy reveals that temperature and moisture contribute roughly equally to the buoyancy in AEWs, while moisture dominates the distribution of buoyancy in PEWs. A scale analysis is performed in order to understand the relative amplitudes of temperature and moisture in easterly waves. It is found that the smaller contribution of temperature to the thermodynamics of PEWs relative to AEWs is related to their slower propagation speed, which allows PEWs to more robustly adjust to weak temperature gradient (WTG) balance. The consistency of the buoyancy analysis and the scale analysis indicates that PEWs are moisture modes: waves in which water vapor plays a dominant role in their thermodynamics. AEWs, on the other hand, are mixed waves in which temperature and moisture play similar roles in their thermodynamics.

Assessment and improvement of RegCM 4.6 coupled with CLM4.5 in simulation of land surface temperature in mainland China

Land surface temperature(LST) is an important indicator to study climate change and test the performance of regional climate model simulation. RegCM4.6 is the representative version of regional climate model RegCM, which is coupled with advanced third-generation land surface model NCAR CLM4.5. Currently, RegCM4.6 has become an important tool to study regional climate change in China. However, its ability to simulate land surface temperature in mainland China and the reasons for its deviation have not been systematically studied, and targeted improvement work is lacking. The present study is the first to employ LST data collected from 809 Chinese meteorological stations from the last 30 years to comprehensively assess the ability of CLM4.5 to simulate LST. Sensitivity tests of soil thermal conductivity (STC) were carried out to improve the model. Although the coupled regional climate model could accurately simulate the temporal and spatial variation of LST, a cold bias of 2~8 °C existed for all of mainland China, which was larger in seasons with more precipitation and greater soil moisture than other seasons. Deviation increased from southeast to northwest. which was caused by the incoming long-wave radiation, sensible heat, and latent heat simulated. There was a significant linear relationship between the observed and simulated LSTs, with correlation coefficients for all the stations ranged from 0.75 to 0.9 (P < 0.001). The observed LST increased at a rate of 0.58 °C/decade, but the simulated LST increased at a lower rate. Assessment of three different STC schemes showed that the Lu-Ren scheme was the most suitable for LST simulation in mainland China. Developing a new STC scheme that considers the role of water vapor can effectively improve the model when used in mainland China.

Wet to Dry Controls Lanthanide Scandate Synthesis

The choice of temperature and gas conditions used in a water pressure-controlled reactor is guided by density functional theory (DFT) to synthesize nearly phase-pure lanthanide scandate nanoparticles (LnScO3, Ln = La, Nd, Sm, Gd). In this synthetic method, low water-vapor partial pressures, well below water's gas liquidus, inhibit particle growth, while an excess of water vapor results in undesired rare-earth hydroxide and oxyhydroxide secondary phases. The optimal humidity for high-purity LnScO3 particle synthesis is shown to vary with the lanthanide; DFT is used to calculate the thermodynamics of secondary phase formation for each lanthanide tested such that the role of water vapor may be quantified and used to maintain phase purity (greater than 96 mol %) across the series. The combination of thermodynamic calculation and experimental confirmation with this pressure-controlled reactor provides an opportunity to explore analogous syntheses of other inorganic perovskite nanoparticles.

The Role of Water Vapor in the Response of the Extratropical Circulation of Earth‐Like Planets to Obliquity Changes

AbstractIn this study, we use idealized aquaplanet simulations of Earth‐like planets to explore the large‐scale atmospheric circulation’s response to changes in shortwave radiation, through changes in the planet obliquity, and in longwave radiation, through changes in the prescribed optical depth. We primarily focus on the extratropical circulation and the counterintuitive weakening of extratropical eddy activity, and associated precipitating storm tracks, with increased obliquity. We show that on high‐obliquity planets with a small surface thermal inertia, net energy deficit during the winter months is primarily balanced by the latent energy component of the atmospheric heat capacity, which buffers any significant atmospheric cooling. As temperatures finally start to decrease, condensational latent heat release of atmospheric moisture further slows down the cooling and keeps the winter pole warmer than the midlatitudes until after the winter solstice. This prevents vigorous baroclinic eddy activity, which lives off the potential energy stored in the sloping isopycnals, as well as the development of a Ferrel cell and storm track. For planets with larger surface heat capacity, we see a similar suppression, with the energy storage in the ocean surface, rather than atmospheric latent energy storage, primarily balancing the net energy loss during the winter months. These results suggest that, regardless of surface thermal inertia, water‐covered high‐obliquity Earth‐like planets would not experience significant extratropical storm activity and highlight the need for a proper characterization of polar properties in planetary modeling and observational investigations.

Separation of isoprene from biologically-derived gas streams

ABSTRACT Renewable organic precursors, including olefinic compounds such as isoprene, have attracted interest from the polymer and pharmaceutical industries. Biologically-derived processes can generate these target compounds; however, their gaseous product streams are complex mixtures of condensable organic vapors (COVs), water vapor, carbon dioxide (CO2), and/or nitrogen (N2). Because COVs, CO2 and water vapor are known to alter polymer membranes, mixed gas separations data at ambient and elevated temperatures are limited. This study focused on two classes of polymer membranes, glassy [polyetherimide (Ultem®)] and a rubbery [polydimethylsiloxane (PDMS)] with results indicating that isoprene separation is possible in humidified gas environment (2–4 vol% water). Gas permeabilities of these membranes did not noticeably change in the presence of humidity; however, the selectivity of these membranes was significantly lower compared to their performance under dry conditions. The role of water vapor in gas transport was derived from the energy of activation of permeation (Ep) for PDMS and Ultem® from 30–80°C in humidified mixed gas streams. For both polymers, Ep data shows a slight decrease in selectivity with the other gases (hydrogen, N2, CO2, and methane) at elevated temperatures in the presence of water vapor. Thus, these COVs separations are feasible with polymer membranes in the presence of humidified gas streams, even in the case of glassy and rubbery membranes in series.

Persistent Photoconductivity in SnO2 Thin Films Grown by Molecular Beam Epitaxy: The Dominant Roles of Water Vapor and Carrier Concentration

Persistent Photoconductivity in SnO₂ Thin Films Grown by Molecular Beam Epitaxy: The Dominant Roles of Water Vapor and Carrier Concentration

The impact of water vapor on the OH reactivity toward CH3CHO at ultra-low temperatures (21.7-135.0K): Experiments and theory.

The role of water vapor (H2O) and its hydrogen-bonded complexes in the gas-phase reactivity of organic compounds with hydroxyl (OH) radicals has been the subject of many recent studies. Contradictory effects have been reported at temperatures between 200 and 400K. For the OH + acetaldehyde reaction, a slight catalytic effect of H2O was previously reported at temperatures between 60 and 118K. In this work, we used Laval nozzle expansions to reinvestigate the impact of H2O on the OH-reactivity with acetaldehyde between 21.7 and 135.0K. The results of this comprehensive study demonstrate that water, instead, slows down the reaction by factors of ∼3 (21.7K) and ∼2 (36.2-89.5K), and almost no effect of added H2O was observed at 135.0K.

Radiometric Measurements of Atmospheric Attenuation Over a Tropical Location

AbstractThe information of atmospheric attenuation at Ka‐band is important during rain and clear air condition. In this paper, Ka‐band attenuation data obtained from radiometric measurements at Kolkata, India (22°034′E, 88°022′N) have been presented. The role of water vapor is examined in determining the behavior of atmospheric attenuation during and without rain condition at 22.24, 26.24, and 31.4 GHz frequencies. It has been observed that at lower rain rate (&lt;5 mm/hr), attenuation at 22.24 GHz is the highest among three frequencies due to water vapor absorption at this frequency. Millimeter Wave Propagation (MPM) model has been used to observe the contribution of rain and water vapor in determining atmospheric attenuation for different rain rates. It has been noted that at 22.24 GHz, water vapor attenuation is comparable to the rain attenuation up to 5 mm/hr. The measured attenuation from radiometer has been compared with ITU‐R model‐generated data and both the attenuation data match reasonably well up to rain rate 20 mm/hr. The attenuation obtained from radiometric measurements shows saturation with increasing rain rate due to the darkening effect. The ITU‐R frequency scaling model has been used to compare the measured and calculated attenuation at 31.4 GHz. This study gives some useful information about the radiometric measurements of atmospheric attenuation at a tropical location that shows that not only rain rate but also water vapor is an important cause of attenuation at Ka‐band.

Role of water vapour in the absorption of nanosecond 266-nm laser pulses by atmospheric air

The absorption of the Nd : YAG fourth harmonic in air and binary mixtures of water vapour with nitrogen and oxygen at atmospheric pressure has been measured as a function of pulse energy (peak intensity). The mixtures obtained by adding equal amounts of water vapour to dry nitrogen and oxygen have been found to differ significantly in absorption. Preliminary quantitative data have been obtained for two- and three-photon absorption cross sections of water and oxygen molecules: σ(2)(H2O) = (4 ± 1) ± 10–49 cm4 s and σ(3)(O2) = (5.6 ± 1.4) ± 10–78 cm6 s2. The absorption of 266-nm pulses with peak intensities from 0.05 to 2 GW cm–2 in the near-surface atmosphere has been shown to be determined by two-photon absorption in water vapour and three-photon absorption in oxygen. In moist air containing 1 % water vapour, the absorption coefficient for 266-nm laser pulses exceeds that in dry air by four to five times. There is no absorption in nitrogen. We have developed a technique for photoacoustic measurements of multiphoton absorption cross sections in single-component gases and gas mixtures.

The role of water vapor during the synthesis of hydrogen doped In2O3

Hydrogen-doped In2O3 synthesized using magnetron sputtering or atomic layer deposition in the presence of water vapor has high transparency in the near infra-red region and mobility values that are almost three to four times of those in commercially used In2O3:Sn at a much lower carrier concentration. However, simple questions like what happens when water molecules enter In2O3 or why the dominant charge carrier changes from an oxygen vacancy in In2O3:Sn to H+ in In2O3 are not clear. Using hybrid functional based density functional theory calculations, we show that water molecules spontaneously split into H+ and OH−. The H+ interstitial bonds with an oxygen in In2O3, and the OH− interstitial occupies a vacant lattice site or is trapped by an oxygen vacancy. Thus, in agreement with experimental findings, our results suggest that the concentration of oxygen vacancies decreases as the partial pressure of water increases. The charge transition level, ϵ(−/+), of a hydrogen interstitial and the Fermi level at which the formation energies of OH− and H+ are equal lie above the conduction band minimum, suggesting that the H+ interstitial has a lower formation energy. In addition, water molecules do not exhibit any propensity to form clusters, meaning that H+ ions can diffuse and remain spatially separated from each other.

(Invited) Plasma-Activated Synthesis of Ammonia Using Nitrogen Gas and Water As Feedstocks

The reduction of nitrogen to ammonia by the Haber-Bosch (H-B) process entails large energy and environmental costs that motivate research on alternative strategies. A major issue with the H-B process is the need for hydrogen gas that currently comes from fossil fuels (steam methane reforming). Plasma activation is a potential alternative as it was historically the first industrial method employed to fix nitrogen, but by oxidation. More recently, plasmas have been combined with solid catalyst materials to reduce nitrogen to ammonia at lower pressures and temperatures than the H-B process, but also use hydrogen gas as a feedstock.Here, we present our efforts to develop plasma-activated processes for the reductive synthesis of ammonia using nitrogen and water as feedstocks. One configuration is a hybrid electrochemical system in which a microplasma jet impinging on an aqueous electrolyte surface replaces a metal electrode and reactions are carried out at the interface of the plasma and liquid bath. A second configuration is a hybrid aerosol system in which water droplets are introduced into a larger-volume plasma and reactions are carried out at the interface of the plasma and droplet surface. In both cases, the ammonia is collected in the liquid phase and measured by chemical assay methods. We will discuss process optimization, product selectivity, and energy consumption for both systems. Insights into the reaction mechanisms will also be addressed and in particular, the possible role of water vapor.

Synergy of steam reforming and K2CO3 modification on wood biomass pyrolysis

The primary objective of this study was to investigate the synergistic effects of K2CO3 and steam reforming in the gasification process of woody biomass for hydrogen production. The experiment was carried out in a fixed-bed reactor with a continuous feeding system to investigate the effect of steam to biomass (S/B) molar ratio (0–0.4), K2CO3 loading amount (0–10 wt%) and reaction temperature (650–850 °C) as three main factors. The experimental results clearly indicated that both S/B and K2CO3 loadings promoted hydrogen production which could reach from 56 to 66% progressively as temperature increased from 650 to 750 °C, the role of potassium carbonate was mainly to change the path of catalytic cracking of tar and reduce the carbon deposit on the surface of the catalyst. While the role of water vapor mainly promoted shifting the reforming reaction in the direction of hydrogen generation. In addition, the water vapor itself could react with carbon to generate more hydrogen. The synergy of K2CO3 modification and steam reforming alleviated the deposited char and changed the components of tar simultaneously, and the optimum value for hydrogen production was acquired with 7.5% K2CO3 loading biomass while the value of S/B was 0.3 as the result of K2CO3 modification. The yield of rich-hydrogen syngas at 650 °C was similar with that of 850 °C, which evidenced that K2CO3 promoted the cracking of biomass at the low temperature region. It was concluded that K2CO3 modification of wood biomass with steam reforming promoted the hydrogen production and changed the path of catalytic cracking of tar and reduced the carbon deposit on the surface of the catalyst.

Modeling of CO2 adsorption and recovery from wet flue gas by using activated carbon

The presence of water vapor complicates the separation and recovery of CO2 from flue gas. Activated carbon is widely regarded as a promising adsorbent for CO2 capture because of its hydrophobicity. However, complete hydrophobicity is impossible, especially at high humidity levels. The effects of water vapor on CO2 capture systems using activated carbon must be further investigated. An adsorption isotherm expression of water vapor on activated carbon named Langmuir + arc-tangent model is presented in this paper, based on which a three-component adsorption equilibrium expression of H2O/CO2/N2 on activated carbon and a complete mathematical model for CO2 adsorption and recovery from wet flue gas by using activated carbon-fixed bed are established. Vacuum swing adsorption (VSA) process for CO2 recovery from wet flue gas under different inlet relative humidity and temperatures are studied, and the role of water vapor on the adsorption and desorption processes of CO2 on activated carbon is revealed. Suggestions that are favorable for CO2 capturing from wet flue gas by using activated carbon under certain conditions are proposed.

Irrigation impacts on minimum and maximum surface moist enthalpy in the Central Great Plains of the USA

Agricultural activities notably alter weather and climate including near-surface heat content. However, past research primarily focused on dry bulb temperature without considering the role of water vapor (dew point temperature) on surface air heat content. When using dry bulb temperature trends to assess these changes, for example, not including concurrent trends in absolute humidity can lead to errors in the actual rate of warming or cooling. Here we examined minimum and maximum surface moist enthalpy, which can be expressed as “equivalent temperature.” Using hourly climate data in the Central Great Plains (Nebraska and Kansas) from 1990 to 2014, the averages and trends of minimum and maximum equivalent temperature (TE_min; TE_max) were analyzed to investigate the potential impacts of irrigation. During the growing season, TE_max averages were significantly higher in irrigated cropland sites compared to grassland sites. This can be explained by increased transpiration linked to irrigation. In addition, TE_max exhibits a decreasing trend in most sites over the growing season. However, the difference of the trends under irrigated croplands and grasslands is not statistically significant. A longer time series and additional surface energy flux experiments are still needed to better understand the relationships among temperature, energy, and land cover.

Untrapping Kinetically Trapped Ions: The Role of Water Vapor and Ion-Source Activation Conditions on the Gas-Phase Protomer Ratio of Benzocaine Revealed by Ion-Mobility Mass Spectrometry.

The role of water vapor in transforming the thermodynamically preferred species of protonated benzocaine to the less favored protomer was investigated using helium-plasma ionization (HePI) in conjunction with ion-mobility mass spectrometry (IM-MS). The IM arrival-time distribution (ATD) recorded from a neat benzocaine sample desorbed to the gas phase by a stream of dry nitrogen and ionized by HePI showed essentially one peak for the O-protonated species. However, when water vapor was introduced to the enclosed ion source, within a span of about 150 ms the ATD profile changed completely to one dominated by the N-protonated species. Under spray-based ionization conditions, the nature and composition of the solvents have been postulated to play a decisive role in defining the manifested protomer ratios. In reality, the solvent vapors present in the ion source (particularly the ambient humidity) indirectly dictate the gas-phase ratio of the protomers. Evidently, the gas-phase protomer ratio established at the confinement of the ions is readjusted by the ion-activation that takes place during the transmission of ions to the vacuum. Although it has been repeatedly stated that ions can retain a "memory" of their solution structures because they can be kinetically trapped, and thereby represent their solution-based stabilities, we show that the initial airborne ions can undergo significant transformations in the transit through the intermediate vacuum zones between the ion source and the mass detector. In this context, we demonstrate that the kinetically trapped N-protomer of benzocaine can be untrapped by reducing the humidity of the enclosed ion source. Graphical Abstract ᅟ.

Enhanced photo-catalytic activity of TiO2 films by removal of surface carbon impurities; the role of water vapor

We have studied the photo-catalytic degradation of acetaldehyde over the surface of TiO2 films under UV light (365nm) irradiation both at dry and humid air conditions using a high vacuum chamber equipped with on-line gas-chromatography as a batch-type reactor. Changes of TiO2 surfaces upon the photo-catalysis experiments were studied by X-ray photoelectron spectroscopy. The competitive adsorption of water and acetaldehyde resulted in the reduction of reaction rate of photo-catalytic degradation of acetaldehyde under the UV light irradiation. The photo-catalytic reaction rate of TiO2 films towards acetaldehyde mineralization increased when the photo-catalysis experiments were performed repeatedly and it was much more pronounced under humid conditions. Our XPS analysis revealed that carbon impurities on the surface of TiO2 films were removed by UV-light driven photo-catalytic mineralization under humid conditions. Water vapor facilitated the photo-catalytic removal of carbon impurities from TiO2 surface generating additional active sites of TiO2 which resulted in the enhanced photo-catalytic activity of TiO2 films.

Space-borne observations of aerosol - cloud relations for cloud systems of different heights

Here, we examine the aerosol - cloud relations over three major urban clusters of China, representative of three different climatic regimes, under different water vapor conditions and cloud heights, using Aerosol Optical Depth at 550nm (AOD), Cloud Fraction (CC), Cloud Optical Depth (COD), Water Vapor (WV) and Cloud Top Pressure (CTP) data from the MODIS instrument. Over all regions and for all seasons, CC is found to increase with increasing AOD, WV and cloud height. Aerosols, at low WV environments and under constant CTP, have less impact on CC than at high WV environments. Furthermore, AOD has a varying influence on COD depending on CTP. Finally, COD is found to increase with height for low and middle height clouds, and with increasing AOD, especially at low AOD. Our results demonstrate that the role of WV in the observed satellite-based aerosol - cloud relations is significant for all cloud heights.

Role of water vapor and convection‐circulation decoupling in MJO simulations by a tropical channel model

AbstractA tropical channel model failed to simulate an observed MJO event. As a means to find reasons for the failure, model errors in water vapor (qv) and other fields were corrected to different extents by nudging towards a global reanalysis product. An MJO metric was developed to quantify the realism of a simulated MJO event in the amplitude and zonal propagation speed of its precipitation and zonal wind at 850 hPa (U850). Results show that correcting errors in qv alone is necessary and sufficient for a realistic simulation of the MJO event. Correcting errors in other fields is insufficient by itself and unnecessary with water vapor correction. For a realistic MJO simulation, error corrections are needed for qv perturbations of the planetary scales (zonal wave number 1–3) together with its zonal mean in both the lower and middle troposphere. Correcting errors in qv at upper levels, planetary‐scale perturbations of any single zonal wave number, synoptic‐scale perturbations, or temporal/zonal means alone is not sufficient for a realistic MJO simulation. Amplitudes of MJO precipitation and U850 are significantly correlated, but their propagation speeds are not. MJO signals in U850 are easier than those in precipitation to improve by correcting errors in qv. In the absence of MJO intrinsic dynamics, inserted MJO signals in qv in a simulation may create a phantom MJO event in precipitation but not in the circulation. This study confirms the existing knowledge on the importance of qv to MJO simulations, sheds new lights on the role of the qv spatial structure, and presents evidence for possible precipitation‐circulation decoupling in MJO simulations.

The role of water vapor in tropical cyclone development

A modeling study suggests that improved hurricane forecasts could result from monitoring atmospheric moisture.

Effect of Water Vapor During Secondary Cooling on Hot Shortness in Fe-Cu-Ni-Sn-Si Alloys

Residual Cu in recycled steel scrap can cause hot shortness when the iron matrix is oxidized. Hot shortness can occur directly after the solid steel is formed from continuous casting as the steel undergoes a cooling process known as secondary cooling where water is first sprayed on the surface to promote cooling. This is followed by a radiant cooling stage where the steel is cooled in air to room temperature. This investigation examines the roles of water vapor, Si content, temperature, and the presence of Sn in a Fe-0.2 wt pct Cu-0.05 wt pct Ni alloy on oxidation, separated Cu and Cu induced-hot shortness during simulations of the secondary cooling process. The secondary cooling from 1473 K (1200 °C) resulted in a slight increase in liquid quantity and grain boundary penetration as compared to the isothermal heating cycles at 1423 K (1150 °C) due to the higher temperatures experienced in the non-isothermal cycle. The addition of water vapor increased the sample oxidation as compared to samples processed in dry atmospheres due to increased scale adherence, scale plasticity, and inward transport of oxygen. The increase in weight gain of the wet atmosphere increased the liquid formation at the interface in the non-Si containing alloys. The secondary cooling cycle with water vapor and the effect of Sn lead to the formation of many small pools of Cu-rich liquid embedded within the surface of the metal due to the Sn allowing for increased grain boundary decohesion and the water vapor allowing for oxidation within liquid-penetrated grain boundaries. The presence of Si increased the amount of occlusion of Cu and Fe, significantly decreasing the quantity of liquid at the interface and the amount of grain boundary penetration.