Estimation Of Vapor Pressure Research Articles

Volatile and Non-Volatile Organic Compounds Stimulate Oviposition by Aphidophagous Predators.

Simple SummaryEvidence that volatile and non-volatile organic compounds stimulate aphid-eating predators to lay eggs is scattered throughout the scientific literature. The objectives of this review are to compile records indicating that organic compounds stimulate egg laying, calculate an egg production ratio for stimulated predators, and determine if the egg production ratio is correlated with vapor pressure and molecular weight of active compounds. Results indicated that both volatile and non-volatile compounds stimulated egg laying behavior by coccinellid beetles and syrphid flies, but not chrysopid lacewings. The egg production ratio was greatest for syrphid flies. Regardless of predator taxa, the egg production ratio was negatively and positively correlated with molecular weight and vapor pressure, respectively. In conclusion, volatile organic compounds stimulate syrphid flies to lay more eggs than coccinellid beetles and chrysopid lacewings. Volatile organic compounds could be used to manipulate predators to lay more eggs in mass rearing systems or on aphid-infested plants in greenhouses or high tunnels. Introduction: Evidence that volatile organic compounds (VOCs) and non-VOCs stimulate oviposition by aphidophagous predators is scattered throughout the literature. The objectives of this review are to (1) compile records indicating that VOCs and non-VOCs are responsible for oviposition stimulation, (2) calculate an egg production ratio (EPR) for stimulated predators, and (3) determine if EPR is correlated with vapor pressure and molecular weight of active compounds. Methods: The USDA (United States Department of Agriculture), National Agricultural Library, online digital catalog system was used to retrieve abstracts, then the full text of manuscripts on oviposition stimulants for predators. Oviposition-stimulating VOCs and non-VOCS were tabulated with molecular weights and vapor pressure estimates. EPRs were calculated for stimulated coccinellids, syrphids, and chrysopids. Results: Both VOCs and non-VOCs stimulated oviposition behavior by coccinellids and syrphids, but not chrysopids. EPR was greatest for syrphids. Two VOCs, (E)-β-farnesene and 3-methyl-2-butenal, stimulated very high EPR values by the syrphid Episyrphus balteatus. Regardless of predator taxa, EPR was negatively and positively correlated with molecular weight and vapor pressure, respectively. Conclusions: Syrphids (rather than coccinellids or chrysopids) produce more eggs in response to VOCs. Organic compounds with low-to-moderate molecular weights and moderate-to-high vapor pressures might be most effective oviposition stimulants for aphidophagous predators.

Indoor secondary organic aerosols: Towards an improved representation of their formation and composition in models.

The formation of secondary organic aerosol (SOA) indoors is one of the many consequences of the rich and complex chemistry that occurs therein. Given particulate matter has well documented health effects, we need to understand the mechanism for SOA formation indoors and its resulting composition. This study evaluates some uncertainties that exist in quantifying gas-to-particle partitioning of SOA-forming compounds using an indoor detailed chemical model. In particular, we investigate the impacts of using different methods to estimate compound vapour pressures as well as simulating the formation of highly oxygenated organic molecules (HOM) via auto-oxidation on SOA formation indoors. Estimation of vapour pressures for 136 α-pinene oxidation species by six investigated methods led to standard deviations of 28-216%. Inclusion of HOM formation improved model performance across three of the six assessed vapour pressure estimation methods when comparing against experimental data, particularly when the NO2 concentration was relatively high. We also explored the predicted SOA composition using two product classification methods, the first assuming the molecule is dominated by one functionality according to its name, and the second accounting for the fractional weighting of each functional group within a molecule. The SOA composition was dominated by the HOM species when the NO2-to-α-terpineol ratio was high for both product classification methods, as these conditions promoted formation of the nitrate radical and hence formation of HOM monomers. As the NO2-to-α-terpineol ratio decreased, peroxides and acids dominated the simple classification, whereas for the fractional classification, carbonyl and alcohol groups became more important.

Estimation of vapor pressures of liquid and solid organic and organometallic compounds at 298.15 K

Equations for vapor pressure VP, as log VP, at 298.15 K for a set of 1016 liquid organic and organometallic compounds have been constructed using Abraham descriptors. The regression standard deviations of 0.28 and 0.31 log units are excellent by comparison with literature values for large data sets. Similar equations for a set of 359 solid organic and organometallic compounds were very poor, but if carboxylic acids were excluded we obtained equations for 261 compounds with standard deviations of 0.62 and 0.66 log units. For the 98 carboxylic acids taken separately we obtained equations with standard deviations of 0.84 and 0.91 log units. Equations for the carboxylic acids were substantially different to those that excluded carboxylic acids, due, we suggest, to the particular dimeric structure of the crystalline carboxylic acids.

Estimation of Vapor Pressures of Solvent + Salt Systems with Quadratic Solvation Relationships

The paper studies quadratic solvation models (QSMs) applied to the numerical simulation of the vapor pressures of solvent systems with a salt effect. Two useful general quadratic solvation relationships are presented within an integration framework, incorporating cumulative physical indices for components and boundary constraints, in conjunction with the vapor pressures of monomolecular fluids calculated from Antoine, Senol, Frost-Kalkwarf and Xiang-Tan equations. Literature data for the vapor pressures of 18 diverse binary (solvent + salt) and ternary (solvent 1 + solvent 2 + salt 3) vapor–liquid equilibrium systems are subjected to the statistical analysis of QSMs via a logarithmic-ratio objective function and cumulative frequency distribution. Essentially, the examined QSMs with twelve (QSM12) and six (QSM6) adjustable coefficients are quite accurate in yielding overall design factors (Fod) lower than 1.015 and 1.08, respectively. The concentration-dependent model (CM) also simulates precisely the observed data with Fod = 1.013 as far as salt effects are concerned. QSM12 models have proven reasonably successful in predicting the vapor pressures of ternary systems with a mean deviation of 2.2%.

Gas Chromatographic Estimation of Vapor Pressures and Octanol–Air Partition Coefficients of Semivolatile Organic Compounds of Emerging Concern

The subcooled liquid-phase vapor pressures (pL298/Pa) and octanol–air partition coefficients (KOA298) at T/K = 298, enthalpies of vaporization (ΔVAPH/kJ·mol–1), and internal energies of phase transfer from octanol to air (ΔOAU/kJ·mol–1) were estimated for synthetic musks, novel brominated flame retardants (N-BFR), organophosphate esters, and ultraviolet filters using the capillary gas chromatographic retention time (GC-RT) method. These compounds, which spanned approximately six and three orders of magnitude for pL298/Pa and KOA298, respectively, were co-chromatographed with one of three reference compounds to give initial estimates of properties at T/K = 298. The initial GC-RT property estimates were subsequently calibrated using 18 compounds that spanned 6 log units for pL298/Pa and 13 compounds covering 4 log units for KOA298. The calibrated log10 pL298/Pa values estimated here ranged from 0.14 ± 0.19 to −9.19 ± 0.29 for cyclopentadecanone to syn-dechlorane plus (syn-DDC-CO), respectively, while the range of log10 KOA298 values was 6.59 ± 0.26 to 11.40 ± 0.23 for cyclopentadecanone to 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99), respectively. The calibrated GC-RT-derived values were highly correlated with, and were within an average of 0.70 log units of, the literature data for compounds with well-established pL298/Pa and KOA298 measured or derived using non-GC-RT methods. Nonpolar compounds were used in this study to estimate the target polar compound data, which may introduce systematic errors. However, the comparison of our GC-RT results against the literature non-GC-RT values shows that the GC-RT methods performed similarly well for estimating both polar and nonpolar target compounds studied in this work.

Property Estimation of Per- and Polyfluoroalkyl Substances: A Comparative Assessment of Estimation Methods.

To accurately predict the environmental fate of per- and polyfluoroalkyl substances (PFAS), high-quality physicochemical property data are required. Because such data are often not available from experiments, assessment of the accuracy of existing property estimation models is essential. The quality of predicted physicochemical property data for a set of 25 PFAS was examined using COSMOtherm, EPI Suite, the estimation models accessible through the US Environmental Protection Agency's CompTox Chemicals Dashboard, and Linear Solvation Energy Relationships (LSERs) available through the UFZ-LSER Database. The results showed that COSMOtherm made the most accurate acid dissociation constant and air-water partition ratio estimates compared with literature data. The OPEn structure-activity/property Relationship App (OPERA; developed through the CompTox Chemicals Dashboard) estimates of vapor pressure and dry octanol-air partition ratios were the most accurate compared with other models of interest. Wet octanol-water partition ratios were comparably predicted by OPERA and EPI Suite, and the organic carbon soil coefficient and solubility were well predicted by OPERA and COSMOtherm. Acid dissociation of the perfluoroalkyl acids has a significant impact on their physicochemical properties, and corrections for ionization were included where applicable. Environ Toxicol Chem 2020;39:775-786. © 2020 SETAC.

Closure to “Evaluation of the Vapor Pressure Models in the Estimation of Actual Vapor Pressure and Evapotranspiration” by Hitesh Upreti and C. S. P. Ojha

Closure to “Evaluation of the Vapor Pressure Models in the Estimation of Actual Vapor Pressure and Evapotranspiration” by Hitesh Upreti and C. S. P. Ojha

Discussion of “Evaluation of the Vapor Pressure Models in the Estimation of Actual Vapor Pressure and Evapotranspiration” by Hitesh Upreti and C. S. P. Ojha

Discussion of “Evaluation of the Vapor Pressure Models in the Estimation of Actual Vapor Pressure and Evapotranspiration” by Hitesh Upreti and C. S. P. Ojha

Assessment of three models for estimating daily net radiation in southern Africa

Accurate quantification of net radiation flux (Rn) is of paramount importance for the estimation of reference evapotranspiration (ET0) rate, which is used to estimate crop water use. A widely recommended Penman-Monteith procedure outlined in the Food and Agriculture Organization (FAO) Irrigation and Drainage Paper No. 56 for estimation of Rn (FAO56- Rn) is often used to estimate Rn. However, the FAO56- Rn model is data-intensive and also requires site-specific calibrations of coefficients to attain a high level of accuracy of Rn estimates. These coefficients are often used without site-specific calibrations as a result of' the lack of large and representative radiative flux measurements in data-scarce regions such as southern Africa and Rn estimates are therefore considered questionable. Assessment of different models in-situ measurements of Rn is critical to identify an alternative approach that could be used for accurate estimation of Rn with minimal data input and without any site-specific calibrations in this region. In this study, two new Rn models, which differ only in the procedures used to compute atmospheric emissivity were proposed. The first model requires measurements of solar irradiance (Rs) maximum and minimum air temperatures (Tair min and Tair max) while the second model requires additional measurements of relative humidity (RHmin and RHmax) for estimation of the actual vapour pressure (eair). Two new Rn models and a widely recommended FAO56- Rn model were evaluated using daily Rn measurements acquired from five sites which represent different climatic and land cover conditions of southern Africa. The results showed that the first model performed better than all the evaluated models at four sites, with regression coefficient (r2) values greater than 0.90 and index of agreement ( d) values greater than 0.97. These findings suggest that the first model presented here is the most promising and suitable to estimate Rn with minimum input data in southern Africa without any site-specific calibrations. The findings of this study can be used to inform the decision on selecting a model to be used for reliable estimates of Rn for improved estimation of crop water requirement in climatic conditions similar to this region.

Estimation of Pure Component Properties, Part 5: Estimation of the Thermal Conductivity of Nonelectrolyte Organic Liquids via Group Contributions

As an extension of the pure component property estimation techniques that we have developed for normal boiling point, critical property data, vapor pressure, and liquid viscosity, a new group contribution method for the prediction of pure component saturated liquid thermal conductivity has been developed. Predictions are solely molecular structure based. Structural group definitions for the method are a modified version of those proposed by Moller et al. for the estimation of saturated vapor pressures. Structural groups were defined in a standardized form and fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. The new method is based on liquid thermal conductivity data for about 330 components after critical evaluation of 110 000 data points for the various phases and nearly 900 components stored in the Dortmund Data Bank. Results of the new method compared favorably to several other estimation methods from the literature. A relative mean deviation in thermal conductivity of 3.87% was observed for a common set of 331 components (6264 data points). By comparison, the Nagvekar and Daubert method, the best literature method in our comparison, produced a relative mean deviation of 7.03% for 206 components. The range of the method is usually from the triple or melting point to the critical point.

The Influence of Gas-phase Chemistry on Organic Haze Formation

Abstract Although photochemically produced organic hazes are common in planetary atmospheres, there have been few experimental investigations of the gas-phase chemistry leading to organic haze formation. We report a laboratory study of the gas-phase compounds formed by far-ultraviolet irradiation of a CH4/N2 mixture. Using high-resolution chemical ionization mass spectrometry (CIMS) we made in situ measurements of gas-phase products up to m/z 400. Organic nitrogen species dominate the mass spectra with smaller contributions from unsaturated hydrocarbons. Using a structural group method to estimate vapor pressures, we calculate that for compounds detected at m/z > 320, ≥50% of the total compound loading (gas + condensed phase) would be present in the condensed (aerosol) phase at 300 K. Using approximations for changes in vapor pressure with temperature, we estimate that ≥50% of the total loading for species with m/z > 110 would be in the aerosol-phase at 150 K, suggesting that the measured compounds may be important for aerosol composition for a range of temperatures. Finally, we leverage the sensitivity and fast time response of the CIMS measurements to investigate how the gas-phase chemistry evolved over the course of the experiment. This analysis shows that hydrocarbons were the initial products followed by the formation of unsaturated organic nitrogen compounds. Higher molecular weight species and alkylamines appear late in the experiment. Comparison of our measurements to chemical mechanisms used to model planetary haze formation suggests that larger molecular weight compounds need to be considered in haze formation chemistry.

Development of a Thermophysical Properties Model for Flowsheet Simulation of Biomass Pyrolysis Processes

A properties model was developed for use in commercial process simulators to model pyrolysis of lignocellulosic biomass. The component list was chosen to enable process simulations based on a recently published lumped pyrolysis kinetics model. Since many of the compounds involved in pyrolysis are not found in simulator databanks, estimation based on available literature data was used to establish missing parameters. Standard solid enthalpy of formation, solid heat capacity, and solid density estimates calculated from the limited experimental data available were prepared for six biomass constituents and nine intermediate and end-products of their pyrolysis. Ideal gas enthalpy of formation and heat capacity, critical property, and vapor pressure estimates were prepared for another four pyrolysis end-products and one biomass component. The estimates were all validated against the closest available experimental data in the literature. The addition of these new components and properties allows thermodynamicall...

Estimation of critical point, vapor pressure and heat of sublimation of pharmaceuticals and their solubility in supercritical carbon dioxide

The critical point and vapor pressure of pharmaceuticals are required in the calculation of their solubility in supercritical fluids by using an equation of state. The experimental critical point of many pharmaceuticals are not accessible due to their temperature sensitivity, also the experimental vapor pressure of many pharmaceuticals are not available at temperatures at which the supercritical extraction is usually accomplished. In this study, four group contribution methods are used to estimate the critical point and acentric factor of eight pharmaceuticals. The estimated properties are evaluated in predicting the vapor pressure and enthalpy of sublimation of the pharmaceuticals by using the Peng Robinson equation of state. The most accurate critical points are employed to calculate the solubility of the pharmaceuticals in the supercritical CO2 by using the Peng Robinson equation combined with two mixing rules. The AARD of 7.28% indicates the good performance of the Wong Sander mixing rule.

Method for estimating vapour pressures based on thermogravimetric measurements with a magnetic suspension balance

In this paper, we report about a fast and straightforward method for estimating vapour pressures of pure liquids from mass loss rates measured with a magnetic suspension balance (MSB). For a measurement, the sample is placed in an open cylinder, attached to the MSB. Nitrogen flows vertically downwards along the sample cylinder to purge all vapour out of the measuring cell of the balance. To determine the total mass transfer of the liquid into the gas phase, the transport process is divided into an internal and an external part. The internal mass transfer takes place inside the sample cylinder and is only based on diffusion while the external mass transfer outside the cylinder consists of diffusion and convection. To describe the external mass transfer, a correlation for the Sherwood number based on numerical data is found. The numerical simulation is validated with experiments using four different alcohols. Furthermore, the influence of the purge gas flow rate and the filling level of the sample cylinder on the evaporation rate are discussed. Lastly, the found equation is tested to calculate vapour pressures of different substances in a range of 100 Pa to 20 kPa. Our results deviate by 10% from literature values. The relative combined expanded uncertainty (P = 95.5%) of the presented method has been calculated to be 12% in the full vapour pressure range considered.

Heat Capacity of Saturated and Compressed Liquid Dimethyl Ether at Temperatures from (132 to 345) K and at Pressures to 35 MPa

Molar heat capacities at constant volume (Cv) of dimethyl ether have been measured with an adiabatic calorimeter. Temperatures range from the triple point to 345 K, and pressures up to 35 MPa. Measurements were conducted on liquid in equilibrium with its vapor and on compressed liquid samples. The samples are of high purity, as verified by chemical analysis. Calorimetric quantities are reported for the two-phase (Cv(2)), saturated-liquid (Cσ or Cx′), and single-phase (Cv) molar heat capacities. Low temperature Cv(2) data were employed to estimate vapor pressures for values less than 340 kPa by applying a thermodynamic relationship between the two-phase internal energy U(2) and the temperature derivatives of the vapor pressure. Vapor pressures were calculated at temperatures as low as the triple-point temperature. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k = 2 and thus a two-...

Modified Trouton’s Rule for the Estimation, Correlation, and Evaluation of Pure-Component Vapor Pressure

Insights from the venerable Trouton’s Rule have been used to guide the development of an applied-thermodynamic method for the estimation, correlation, and evaluation of pure-component vapor pressure. Trouton’s Rule very simply and succinctly states that the entropy of vaporization of fluids at their normal boiling point is a constant (≈10.5 times the gas constant). Detailed evaluation of the data for many families of chemical compounds reveals the subtle patterns of departures from the rule, and facilitates the development of a useful new correlation. Several examples are presented to demonstrate the value of the new correlation to estimate, correlate, extrapolate, and evaluate vapor-pressure data, and to understand the patterns of vapor-pressure behavior. The methodology provides a guide for the development of thermodynamic correlations, and the resulting correlations are expected to be useful for the practice of applied thermodynamics.

Daily reference crop evapotranspiration with reduced data sets in the humid environments of Azores islands using estimates of actual vapor pressure, solar radiation, and wind speed

Reference crop evapotranspiration (ETo) estimations using the FAO Penman-Monteith equation (PM-ETo) require a set of weather data including maximum and minimum air temperatures (T max, T min), actual vapor pressure (e a), solar radiation (R s), and wind speed (u 2). However, those data are often not available, or data sets are incomplete due to missing values. A set of procedures were proposed in FAO56 (Allen et al. 1998) to overcome these limitations, and which accuracy for estimating daily ETo in the humid climate of Azores islands is assessed in this study. Results show that after locally and seasonally calibrating the temperature adjustment factor a d used for dew point temperature (T dew) computation from mean temperature, ETo estimations shown small bias and small RMSE ranging from 0.15 to 0.53 mm day−1. When R s data are missing, their estimation from the temperature difference (T max−T min), using a locally and seasonal calibrated radiation adjustment coefficient (k Rs), yielded highly accurate ETo estimates, with RMSE averaging 0.41 mm day−1 and ranging from 0.33 to 0.58 mm day−1. If wind speed observations are missing, the use of the default u 2 = 2 m s−1, or 3 m s−1 in case of weather measurements over clipped grass in airports, revealed appropriated even for the windy locations (u 2 > 4 m s−1), with RMSE < 0.36 mm day−1. The appropriateness of procedure to estimating the missing values of e a, R s, and u 2 was confirmed.

Daily reference crop evapotranspiration in the humid environments of Azores islands using reduced data sets: accuracy of FAO-PM temperature and Hargreaves-Samani methods

Reference crop evapotranspiration (ETo) estimations using the FAO Penman-Monteith equation (PM-ETo) require several weather variables that are often not available. Then, ETo may be computed with procedures proposed in FAO56, either using the PM-ETo equation with temperature estimates of actual vapor pressure (e a) and solar radiation (R s), and default wind speed values (u 2), the PMT method, or using the Hargreaves-Samani equation (HS). The accuracy of estimates of daily e a, R s, and u 2 is provided in a companion paper (Paredes et al. 2017) applied to data of 20 locations distributed through eight islands of Azores, thus focusing on humid environments. Both estimation procedures using the PMT method (ETo PMT) and the HS equation (ETo HS) were assessed by statistically comparing their results with those obtained for the PM-ETo with data of the same 20 locations. Results show that both approaches provide for accurate ETo estimations, with RMSE for PMT ranging 0.48–0.73 mm day−1 and for HS varying 0.47–0.86 mm day−1. It was observed that ETo PMT is linearly related with PM-ETo, while non-linearity was observed for ETo HS in weather stations located at high elevation. Impacts of wind were not important for HS but required proper adjustments in the case of PMT. Results show that the PMT approach is more accurate than HS. Moreover, PMT allows the use of observed variables together with estimators of the missing ones, which improves the accuracy of the PMT approach. The preference for the PMT method, fully based upon the PM-ETo equation, is therefore obvious.

Estimation of Vapor Pressures and Enthalpies of Vaporization of Biodiesel-Related Fatty Acid Alkyl Esters. Part 2. New Parameters for Classic Vapor Pressure Correlations

In Part I of this series of articles, predictive models capable of estimating vapor pressures and enthalpies of vaporization of biodiesel-related esters have been reviewed. In this study, we propose component-specific parameters for classic vapor pressure correlations. First, the previously collected database was evaluated and used in the regression of Antoine coefficients for all compounds. Then, a constrained regression methodology was employed to generate extrapolatable Wagner parameters for the esters whose experimental critical properties were available. Finally, expressions derived from the Clausius–Clapeyron equation have been investigated for the estimation of enthalpies of vaporization. A comparative analysis of the results produced by our parameters and by others available in the literature encourages the use of our values in future applications.

Measured Saturation Vapor Pressures of Phenolic and Nitro-aromatic Compounds.

Phenolic and nitro-aromatic compounds are extremely toxic components of atmospheric aerosol that are currently not well understood. In this Article, solid and subcooled-liquid-state saturation vapor pressures of phenolic and nitro-aromatic compounds are measured using Knudsen Effusion Mass Spectrometry (KEMS) over a range of temperatures (298-318 K). Vapor pressure estimation methods, assessed in this study, do not replicate the observed dependency on the relative positions of functional groups. With a few exceptions, the estimates are biased toward predicting saturation vapor pressures that are too high, by 5-6 orders of magnitude in some cases. Basic partitioning theory comparisons indicate that overestimation of vapor pressures in such cases would cause us to expect these compounds to be present in the gas state, whereas measurements in this study suggest these phenolic and nitro-aromatic will partition into the condensed state for a wide range of ambient conditions if absorptive partitioning plays a dominant role. While these techniques might have both structural and parametric uncertainties, the new data presented here should support studies trying to ascertain the role of nitrogen containing organics on aerosol growth and human health impacts.