Total Vapor Pressure Research Articles

The capability of 20th‐century reanalyses to reproduce the spatiotemporal variation in surface incident solar radiation over Japan for 1931–2010

AbstractUnderstanding the spatiotemporal variations in surface incident solar radiation (Rs), especially over longer time spans, is crucial for climate modeling and environmental assessment. This study, referring to the century‐long homogenized Rs measurements, comprehensively quantifies the ability of five 20th‐century reanalyses phenomena to estimate Rs over Japan for 1931–2010, and furthermore assesses the contributions of total cloud cover and vapor pressure to the biases in Rs trends. Dominant features revealed that Rs signals boost from the north to the south, which could be captured but is overestimated by all reanalyses. The dominant time evolution of Rs was well captured by CERA20C, followed by ERA20C and 20CRv3, corresponding to their relatively better performance cloud cover. Unfortunately, ERA20CM totally fails to reproduce the spatiotemporal variation in Rs as its procedure does not include an assimilation step. 20CRv2c fails in estimating Rs for 1931–1960, but improves much for 1961–2010 as the quality of assimilated observational variables becomes better. A dimming of −2.76 W·m−2·decade−1 for 1931–1960 was detected in the observed Rs, which could be reproduced by CERA20C and ERA20C. Afterwards, a brightening of 0.88 W·m−2·decade−1 for 1961–2010 was shown in observations, and all reanalyses fail. The trend bias of Rs in CERA20C attributes more to total cloud cover before 1960, and to aerosols or other factors after 1960. Cloud cover contributed more than vapor pressure to the trend bias of Rs for 1931–1960; vapor pressure became more important in regulating Rs for 1961–2010 than for 1931–1960. The combined effects of both factors on Rs are insignificant for 20CRv3 during the entire period, for 20CRv2c for 1931–1960 and for CERA20C for 1961–2010, suggesting other factors, such as aerosols, cloud types, cloud optical depth and their interactions may impact Rs simulations more and this calls for further investigation.

High Temperature Mass Spectrometric Study of Vaporization of The Oxycarbide Ceramics Based on the MAX-Phases

In the present study, the vaporization processes of the carbide materials with the Ti2SiC, Ti3SiC2, Ti2AlC, Ti3AlC2, Zr2AlC, Zr3AlC2 chemical compositions containing the MAX-phases as well as the oxycarbide systems based on these materials with the addition of hafnia were examined by the Knudsen effusion mass spectrometric method up to the temperature 2200 K. It was established that the main vapor species over the samples with the Ti2AlC, Ti3AlC2, Zr2AlC, and Zr3AlC2 compositions at the temperature 1500 K was atomic aluminum. The samples containing silicon were less volatile compared to the carbide materials with aluminum and transferred into vapor at temperatures exceeding 1900 K to form gaseous Si, Si2, SiC2, and Si2C. The addition of hafnia to the carbides under study led to the formation of oxygen-containing vapor species, particularly Al2O and SiO, and to decrease in the total vapor pressure over the systems formed. It was shown that the samples of the oxycarbide Ti2SiC-HfO2 system were the least volatile materials, and, among the oxycarbide systems containing aluminum, the lowest volatility was observed for the samples of the Zr2AlC-HfO2 system in the case of the hafnia content up to 10 mol. % and of the Ti2AlC-HfO2 system for the higher HfO2 concentration.

Divergent trajectories of future global gross primary productivity and evapotranspiration of terrestrial vegetation in Shared Socioeconomic Pathways

Understanding the future trends of carbon and water fluxes between terrestrial ecosystems and the atmosphere is crucial for predicting Earth's climate dynamics. This study employs an advanced numerical approach to project global gross primary productivity (GPP) and evapotranspiration (ET) from 2001 to 2100 under various climate scenarios based on Shared Socioeconomic Pathways (SSPs). To improve predictions of vegetation dynamics, we introduce a novel model (CoLM-PVPM), an enhancement of the Common Land Model version 2014 (CoLM2014), incorporating a prognostic vegetation phenology model (PVPM). Compared to CoLM2014 that relies on satellite-based leaf area index (LAI) inputs, CoLM-PVPM predicts LAI time series using climate variables. Model validation using historical data from 2001 to 2010 demonstrates PVPM in capturing spatiotemporal variations in satellite LAI. Our modeling results indicate that annual averaged LAI and total GPP increase under SSP1–2.6 but decrease under SSP2–4.5, SSP3–7.0, and SSP5–8.5 by 2100. By comparison, annual total ET consistently increases under all SSP scenarios by 2100. Global annual averaged LAI is highly correlated with annual total GPP in all scenarios, while its correlation with annual total ET weakens in SSP2–4.5, SSP3–7.0, and SSP5–8.5. Global annual total vapor pressure deficit (VPD) and precipitation are highly correlated with annual total ET in all scenarios. As emission levels increase, the negative correlation between annual total VPD and GPP strengthens, while the correlation between annual total precipitation and GPP weakens. This research presents an improved model for predicting terrestrial vegetation processes and underscores the importance of low carbon emission scenarios in maintaining carbon-water balances in specific regions.

Assessment of the Equivalence of Methods for the Determination of the Vapor Pressure of Oil and Oil Products

Current regulatory documents in Russia establish the need for testing laboratories to determine such parameters as saturated vapor pressure using the Reid method, air saturated vapor pressure, total vapor pressure of crude oil. In analytical practice, appropriate reference materials are used for measurement quality control, method validation, metrological traceability establishment, and other purposes. In addition, the calculation of various vapor pressure equivalents using correlation equations (DVPE – dry vapor pressure equivalent, RVPE – Reid vapor pressure equivalent, etc.) is regulated by appropriate methods for determining vapor pressure. Vapor pressure is a method-dependent parameter; so many producers of reference materials use interlaboratory experiment as a way to establish a certified value. Thus, when conducting an interlaboratory experiment in the process of certification of reference materials, it was revealed that laboratories can incorrectly interpret the obtained experimental data – consider values of the air saturated vapor pressure, total vapor pressure and even calculated vapor pressure equivalents as the Reid vapor pressure. To solve this problem, the authors of this work set the goal of assessing the equivalence of methods for determining the vapor pressure of oil and oil products used in testing laboratories in order to identify the key characteristics of the stated methods and assess their equivalence. The article discusses methods the vapor pressure determination using an automatic vacuum chamber and a Reid bomb. Various matrices of reference materials (hydrocarbons, gasoline, commercial oil, gas condensate) were investigated, and the calculated vapor pressure equivalents were obtained and compared. It was shown that the air saturated vapor pressure, dry vapor pressure equivalent, Reid vapor pressure equivalent, and total vapor pressure cannot be equated to the saturated vapor pressure values determined by the Reid method. A comparative assessment of methods for determining the vapor pressure of oil and oil products used in testing laboratories can be of assistance to developers of regulatory documents for oil, gas condensate, and motor gasoline, revealing the need to separate the requirements for vapor pressure parameters of the considered objects of analysis and providing empirical material.

THERMODYNAMICS OF LIQUID–GAS PHASE EQUILIBRIA OF DIISOPROPYLSULFOXIDE–WATER SYSTEM

The saturated vapor pressure of diisopropylsulfoxide aqueous solutions was measered at temperatures of 303.15 K and 308.15 K. It was shown that the total saturated vapor pressure increases with decreasing diisopropylsulfoxide concentration in the solution and with increasing temperature. As in the cases of diethylsulfoxide and dipropylsulfoxide aqueous solutions, a negative deviation from Raoult’s law is also observed. This confirms the ability of diisopropylsulfoxide molecules to associate with water molecules. Based on the results obtained, the partial pressures, the activity coefficients of diisopropylsulfoxide and water and the excess Gibbs energy of their mixing, were calculated. It is shown that the excess Gibbs energy of mixing is negative and reaches its minimum value at a mole fraction of diisopropylsulfoxide equal to 0.38. The obtained data on the excess Gibbs energy of mixing DiPSO and water were treated using the Redlich–Kister equation. It has been established that the interaction between the molecules of diisopropylsulfoxide and water is stronger than in the diethylsulfoxide+water system, and weaker than in the dipropylsulf-oxide+water system. This fact can be explained by an increase in the electron-donating ability of the alkyl group with increasing hydrocarbon chain length, which increases the reactivity of the oxygen atom of the sulfoxide group. As a result, when moving from diethylsulfoxide to diisopropylsulfoxide or dipropylsulfoxide, the ability of their molecules to interact with water molecules to form hydrogen bonds increases. At the same time, a decrease in hydrophobic effects and dispersion forces between diisopropylsulfoxide molecules with a branched hydrocarbon chain leads to a weakening of the interaction between molecules in the diisopropylsulfoxide+water system compared to the dipropylsulfoxide+water system, which is also observed experimentally.

Obtaining Multicomponent Coatings of a Stable Composition for Electromagnetic Radiation Screens

The formation processes of coatings of Cu–Ni and Ag–Cu systems with a stable elemental composition by the method of electron-beam evaporation are considered. It is shown that in the zone of action of the electron beam on the ingot placed in the crucible at the total vapor pressure of the alloy elements Σp above the pressure under the cap of the installation, the melt boils, and in the outer zone adjacent to the melt zone, the process of sublimation of the hard alloy occurs. The microrelief and elemental composition of the surface layer of the Cu–Ni alloy ingot in the zones of evaporation and sublimation, as well as the elemental composition of the coatings deposited in this case, have been studied. It is shown that the most acceptable way to obtain coatings of the Cu–Ni system with a stable elemental composition is the simultaneous electron-beam evaporation of copper and nickel from two crucibles. The azeotropic composition of the alloy of the Ag–Cu system was calculated and experimentally verified. The research results are used in the manufacture of multilayered screens of electromagnetic radiation.

EVAPORATION THERMODYNAMICS FOR SOLUTIONS OF DIMETHYLZINC AND DIMETHYLTELLURIDE

In the work with the help of a static method with a membrane zero-manometer, the liquid- vapor balance in the system “dimethylzinc – dimethyl telluride” in the temperature range 270– 360 K with the content of dimethylzinc as 50.00 and 70.32 % mol. The total vapor pressure was measured for both saturated and unsaturated vapors for different samples. It was found that these solutions are not azeotropic. Using the equation of state PV = nRT, according to the thermal expansion of unsaturated vapor, the average molecular weight was calculated for mixtures “dimethylzinc – dimethyltelluride” mentioned compositions. The results of this calculation indicate the absence of significant association between molecules of the solution components in the gas phase.

Comparison of different machine learning approaches for tropospheric profiling based on COSMIC-2 data

Precise and reliable information on the tropospheric temperature and water vapor profiles play a key role in weather and climate studies. Among the sensors supporting the observations of the troposphere, one can distinguish the Global Navigation Satellite System Radio Occultation (RO) technique, which provides accurate and high-quality meteorological profiles. However, external knowledge about temperature is essential to estimate other physical atmospheric parameters. To overcome this constraint, I trained and evaluated four different machine learning models comprising Artificial Neural Network (ANN) and Random Forest regression algorithms, where no auxiliary meteorological data is needed. To develop the models, I employed 150,000 globally distributed (45°S–45°N) RO profiles between October 2019 and December 2020. Input vectors consisted of bending angle or refractivity profiles from the Formosa Satellite-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 mission together with the month, hour, and latitude of the RO event. While temperature, pressure, and water vapor profiles derived from the modern ERA5 reanalysis and interpolated to the RO location served as the models’ targets. Evaluation on the testing data set revealed a good agreement between all model outputs and ERA5 targets, where slightly better statistics were noted for ANN and refractivity inputs. Vertically averaged root mean square error (RMSE) did not exceed 1.7 K for the temperature and reached around 1.4 hPa and 0.45 hPa for the total and water vapor pressures. Additional validation with 477 co-located radiosonde observations and the operational one-dimensional variational product showed slightly larger discrepancies with the mean RMSE of around 1.9 K, 1.9 hPa, and 0.5 hPa for the temperature, pressure, and water vapor, respectively.Graphical

Comparison of the Deep Learning Performance for Short-Term Power Load Forecasting

Electricity demand forecasting enables the stable operation of electric power systems and reduces electric power consumption. Previous studies have predicted electricity demand through a correlation analysis between power consumption and weather data; however, this analysis does not consider the influence of various factors on power consumption, such as industrial activities, economic factors, power horizon, and resident living patterns of buildings. This study proposes an efficient power demand prediction using deep learning techniques for two industrial buildings with different power consumption patterns. The problems are presented by analyzing the correlation between the power consumption and weather data by season for industrial buildings with different power consumption patterns. Four models were analyzed using the most important factors for predicting power consumption and weather data (temperature, humidity, sunlight, solar radiation, total cloud cover, wind speed, wind direction, humidity, and vapor pressure). The prediction horizon for power consumption forecasting was kept at 24 h. The existing deep learning methods (DNN, RNN, CNN, and LSTM) cannot accurately predict power consumption when it increases or decreases rapidly. Hence, a method to reduce this prediction error is proposed. DNN, RNN, and LSTM were superior when using two-year electricity consumption rather than one-year electricity consumption and weather data.

Total vapor pressure of hydrophobic deep eutectic solvents: Experiments and modelling

Headspace gas chromatography mass spectrometry (HS-GC–MS) was used to determine the volatility of six selected hydrophobic deep eutectic solvents (DESs). The partial pressure of each DES constituent (decanoic acid, thymol, 1-tetradecanol, menthol or lidocaine) was measured from 313.15 to 373.15 K. The activity coefficients of the hydrogen bond acceptor (HBA) and the hydrogen bond donor (HBD) were determined to quantify the interactions between the DES constituents, thereby deepening the understanding of the thermodynamic nature of the DESs. In addition, the activity coefficients for both components in each DES were predicted with the UNIFAC group contribution method. Similar trends and reasonably close values were obtained for the measured and predicted activity coefficients. It has been found that the interactions between the DES constituents tend to become weaker with increasing temperature. Strong interactions occur between thymol and lidocaine, and thymol interacts moderately with menthol. A weak force exists between decanoic acid and menthol. The mixtures of menthol with 1-tetradecanol or lidocaine are not strictly DESs since for each DES constituent both the measured and predicted activity value is close to unity. A viscosity study was also carried out to quantify the interactions and similar results were found. The ideal mixing rule was proven to correctly describe the viscosity for the mixture of menthol with 1-tetradecanol or lidocaine. While compared to the ideal mixture viscosity, an increase in viscosity was observed for other studied DESs indicating stronger interactions. Finally, the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was shown to accurately describe the thermodynamic properties, where the PC-SAFT pure-component parameters for the DESs were obtained by fitting to pure DES density and total vapor pressure data.

An approach to gas sensors based on tunable diode laser incomplete saturated absorption spectra* *Project supported by the Guangdong Province Key Laboratory of Efficient and Clean Energy Utilization (Grant No. 2013A061401005) and the Key Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes (Grant No. KLB10004).

A spectral profile reconstruction method that can be applied to incomplete saturated-absorption spectra is proposed and demonstrated. Through simulation and theoretical calculation, it is proved that compared with the traditional whole-profile fitting method, this new method can increase the concentration detection upper limit of a single absorption line by about 8.7 times. High-concentration water vapor is measured using TDLAS technology, the total water vapor pressure and the self-broadened half-width coefficient of the spectrum were simultaneously measured from incomplete saturated-absorption spectra and compared with high-precision pressure sensors and the HITRAN databases. Their maximum relative deviations were about 4.63% and 9.10%, respectively. These results show that the spectral profile reconstruction method has great application potential for expanding the dynamic range of single-line measurements to higher concentrations, especially for in-situ online measurements under complex conditions, such as over large temperature and concentration dynamic ranges.

Determination of the molecular size from measurements of vapour pressure of binary liquid mixtures. Theory, experiments and quantum chemical calculations

In the present work we focus on some fundamental organic solvents. The total and partial vapour pressure of 30 binary systems made of hexane, cyclohexane, and benzene with 10 organic molecules, namely chloroform (Chl), chlorobenzene (Cl-Ben), tetrahydrofuran (THF), dichloromethane (DCM), acetone (Ac), ethanol (EtOH), N, N-dimethylformamide (DMF), methanol (MeOH), acetonitrile (MeCN) and dimethylsulphoxide (DMSO), were measured using the method developed by Sameshima. A simple electrostatic model was derived to express the change of the Helmholtz free energy as a function of dielectric properties of the binary mixtures, as well as the dielectric constant, dipole moment, dipole polarizability, and radius of a spherical cavity hosting the aforementioned 10 organic molecules. Through measurements of the partial vapour pressure of these 10 organic liquids, the size of the cavity was extracted, which approximates their molecular size. The molecular size obtained from the experiments exhibits a good agreement with the results as obtained from the cavity size calculated using the Polarizable Continuum Model (PCM). The partial vapour pressure of some compounds such as Ac, DMF, DMSO, and MeCN presented severe deviation from the Raoult law. The intermolecular interaction among the molecules of each compound was believed to take responsibility for their exceptional behaviours in vapour pressure.

Simple Model for Diffusion-Limited Drop Evaporation of Binary Liquids from Physical Properties of the Components: Ethanol-Water Example.

The understanding of the evaporation process of drops consisting of binary mixtures, in particular ethanol-water drops, is important in many industries such as ink-jet printing, cooling of microelectronics, and alcohol-added pesticide spray applications. The theory of the diffusion-limited drop evaporation process for pure liquids has been investigated thoroughly, and linear (dV(2/3)/dt) slopes were obtained for most of the cases. However, the evaporation of binary liquid drops was found to be much more complicated than that of the pure liquids due to the change of the composition of the drop by time and there is a need for the development of a new model. The experimental results on the diffusion-limited drop evaporation behavior of ethanol-water binary drops initially containing 25 and 50% ethanol by wt and having a volume of 7 μL were reported on a flat hydrophobic Teflon-FEP substrate under the constant relative humidity of 54% and 25 °C temperature conditions, together with pure liquids. The change of contact angles, heights, and contact radius of the drops by time were monitored with a camera. In a parallel study, the concentration changes in the bulk composition of ethanol-water binary drops of 7 μL (25 and 50% ethanol by wt) by time in the same evaporation conditions were monitored using a refractive index-ethanol concentration calibration curve. Then, the parameters affecting the drop evaporation process, such as total vapor pressures, average diffusion coefficient of binary vapors, average molecular weights, and densities of the liquid drops, were calculated using well-known physical chemistry approaches from the previously published data. These parameters were used to estimate the rate of binary ethanol-water drop evaporation, and it was determined that the proposed model fitted the (dV(2/3)/dt) slopes obtained from experimental data points with lower than 5% error when the surface cooling of the drops was considered.

Vaporization behaviour of a PuF3-containing fuel mixture for the Molten Salt Fast Reactor

The mixture LiF-ThF4-UF4-PuF3 (77.5–6.6-12.3–3.6 mol%), a fuel option for the Molten Salt Fast Reactor (MSFR), has been measured by differential scanning calorimetry (DSC) for determination of phase transitions, and by Knudsen effusion mass spectrometry (KEMS) for measurement of partial vapour pressures. The boiling point of the mixture was determined by extrapolation of total vapour pressure to 1 bar. Thermodynamic calculations were performed and compared with the experimental results. Novel experimental data on pure plutonium trifluoride are presented: melting point, vaporization enthalpy, vapour pressure and ionization energies by electron impact.

Determination of the Total Vapor Pressure of Hydrophobic Deep Eutectic Solvents: Experiments and Perturbed-Chain Statistical Associating Fluid Theory Modeling

Head-space gas chromatography mass spectrometry (HS-GC-MS) was used for the first time to measure the total vapor pressure of hydrophobic deep eutectic solvents (DESs). The new method was developed as a valid alternative for thermogravimetric analysis (TGA), as TGA did not allow obtaining reliable total vapor pressure data for the hydrophobic DESs studied in this work. The main advantage of HS-GC-MS is that the partial pressure of each DES constituent and the contribution of each DES constituent to the total vapor pressure of the mixture can be measured. The results give a clear indication of the interactions occurring between the DES constituents. Also, activity coefficients, enthalpies of evaporation, and activation energies for fluid displacement were obtained and correlated to the measured vapor pressure data. It was confirmed that the total vapor pressures of the hydrophobic DESs are very low in comparison to vapor pressures of commonly used volatile organic solvents like toluene. The total vapor pre...

Vapor pressure measurements of AgBr by the Knudsen effusion method

The vapor pressure of silver bromide (AgBr) liquid was measured by the Knudsen effusion method. The ratio of the vapor species of silver bromide was calculated from the literature Hildenbrand and Lau, Pankratz [3,6], and the vapor pressures were calculated on the basis of the ratio. As reported in the literature Hildenbrand and Lau [3], we considered the vapor species to be monomers (AgBr) and trimers (Ag3Br3). The partial pressures of AgBr [pmonomer(Pa)] and Ag3Br3 [ptrimer(Pa)] were respectively fitted by the following linear equations over the temperature range 829.9–929.9 K:lnpmonomer= -(23590 ± 519) / T + 25.22 ± 0.59,ln(ptrimer) = -(19449 ± 509) / T + (20.42 ± 0.58).The total vapor pressure of silver bromide [ptotal(Pa)] fitted the following linear equation:ln(ptotal) = -(21653 ± 529) / T + (23.72 ± 0.60).

The impacts of the activity coefficient on heating and evaporation of ethanol/gasoline fuel blends

The evolutions of droplet radii and temperatures for ethanol and gasoline fuels and their blends are investigated using a modified version of the Discrete Component (DC) model, taking into account the effect of the activity coefficient (AC). The universal quasi-chemical functional–group AC (UNIFAC) model is used to predict the ACs of the blended ethanol and gasoline fuels approximated by 21 components. In contrast to previous studies, it is shown that droplet lifetimes predicted for pure gasoline are not always shorter than those predicted for ethanol/gasoline blends. They depend on the total vapour pressure of the mixture. It is shown that the original DC model predicts ethanol/gasoline fuel droplet lifetimes with errors up to 5.7% compared to those predicted using the same model but with the ACs obtained from the UNIFAC model.

The Thermochemistry of Crystalline M3AlF6, NaAlF4, KAlF4 and Gaseous MAlF4 Fluoroaluminates of Alkali Metals, M

The formation enthalpies of crystalline M3AlF6 and gaseous MAlF4 are confirmed and refined and the formation enthalpy of KAlF4(cryst.) is estimated for MF–AlF3 systems (M is Li, Na, or K) with a minimum in the total saturated vapor pressure.

Responses of Tree Transpiration and Growth to Seasonal Rainfall Redistribution in a Subtropical Evergreen Broad-Leaved Forest

Precipitation changes such as more frequent drought and altered precipitation seasonality may impose substantial impacts on the structure and functioning of forest ecosystems. A better understanding of tree responses to precipitation changes can provide fundamental information for the conservation and management of forests under future climate regimes. We conducted a 2-year seasonal rainfall redistribution experiment to assess the responses of tree transpiration and growth to manipulated precipitation changes in a subtropical evergreen broad-leaved forest. Three precipitation treatments were administered including a drier dry season and wetter wet season treatment (DD), an extended dry season and wetter wet season treatment (ED), and an ambient control treatment, with the total amount of annual rainfall being kept the same among the three treatments. Our results showed that the DD and ED treatments reduced daily transpiration of Schima superba by 8–16 and 13–25%, respectively. The ED treatment also reduced the DBH increment of larger S. superba individuals. In contrast, neither treatment showed obvious effects on the transpiration and DBH increment of another dominant species Michelia macclurei. However, the transpiration of both species showed clear inter-annual differences between the 2 years with contrasting annual rainfall (2094 vs 1582 mm). S. superba had a lower transpiration-to-precipitation ratio (T/P) compared to M. macclurei and showed decreased sensitivities to total solar radiation and vapor pressure deficit under the DD and ED treatments. These results indicate the deep-rooted S. superba may be suppressed with a lower ability to obtain water and assimilate carbon compared to the shallow-rooted M. macclurei under the precipitation seasonality changes, which could potentially cause shifts in species dominance within the forest community.

Vaporization and thermodynamics of forsterite-rich olivine and some implications for silicate atmospheres of hot rocky exoplanets

We describe an experimental and theoretical study of olivine [Mg2SiO4 (Fo)–Fe2SiO4 (Fa)] vaporization. The vaporization behavior and thermodynamic properties of a fosterite-rich olivine (Fo95Fa5) have been explored by high-temperature Knudsen effusion mass spectrometry (KEMS) from 1750 to 2250K. The gases observed (in order of decreasing partial pressure) are Fe, SiO, Mg, O2 and O. We measured the solidus temperature (∼2050K), partial pressures of individual gases, the total vapor pressure, and thermodynamic activities and partial molar enthalpies of MgO, ‘FeO’, and SiO2 for the Fo95Fa5 olivine. The results are compared to other measurements and models of the olivine system. Our experimental data show olivine vaporizes incongruently. We discuss this system both as a psuedo-binary of Fo-Fa and a psuedo-ternary of MgO–‘FeO’–SiO2. Iron/magnesium molar ratios in the sample before (∼0.05) and after (∼0.04) vaporization are consistent with the small positive deviations from ideality of fayalite (γ ∼ 1.17) in olivine of the composition studied (e.g., Nafziger and Muan, 1967). Our data for olivine+melt confirm prior theoretical models predicting fractional vaporization of Fe relative to Mg from molten silicates (Fegley and Cameron, 1987; Schaefer and Fegley, 2009; Ito et al., 2015). If loss of silicate atmospheres occurs from hot rocky exoplanets with magma oceans the residual planet may be enriched in magnesium relative to iron.