Mass Accommodation Coefficient Research Articles

Shining New Light on the Kinetics of Water Uptake by Organic Aerosol Particles.

The uptake of water vapor by various organic aerosols is important in a number of applications ranging from medical delivery of pharmaceutical aerosols to cloud formation in the atmosphere. The coefficient that describes the probability that the impinging gas-phase molecule sticks to the surface of interest is called the mass accommodation coefficient, αM. Despite the importance of this coefficient for the description of water uptake kinetics, accurate values are still lacking for many systems. In this Feature Article, we present various experimental techniques that have been evoked in the literature to study the interfacial transport of water and discuss the corresponding strengths and limitations. This includes our recently developed technique called photothermal single-particle spectroscopy (PSPS). The PSPS technique allows for a retrieval of αM values from three independent, yet simultaneous measurements operating close to equilibrium, providing a robust assessment of interfacial mass transport. We review the currently available data for αM for water on various organics and discuss the few studies that address the temperature and relative humidity dependence of αM for water on organics. The knowledge of the latter, for example, is crucial to assess the water uptake kinetics of organic aerosols in the Earth's atmosphere. Finally, we argue that PSPS might also be a viable method to better restrict the αM value for water on liquid water.

Evaluation of Mass Accommodation Coefficients of Water over a Wide Temperature Range and Determination of Diffusion Coefficient of Water in Nitrogen

Diffusion coefficient of water in nitrogen (Dvg) is a critical thermophysical parameter. However, the widely used empirical parametrizations of Dvg are only applicable in the temperature range from 273 K to 373 K. In the supercooled range, the reported experimental values of Dvg is sparse, and Dvg varies with temperature in a way different from the empirical equations and the recently reported first-principles calculation. In this paper, Dvg values at given temperatures, including in the supercooled range, were determined using the evaporation kinetics of individual water droplets in nitrogen flow under well-controlled conditions. The KVH model capable of describing the rapid evaporation/condensation process of an individual water droplet was utilized, and the thermophysical/kinetic parameters were evaluated carefully. Through reviewing the literature values of mass accommodation coefficient (αM) for ice, ice with liquid-like layer, supercooled water, normal water, and hot water, it is observed that the Slogistic1 function presented by OriginPro® could describe the temperature dependence of αM well. Then, the radius vs. time curve of an individual water droplet was predicted from the KVH model by varying Dvg and then compared with the experimental curve recorded by the Electrodynamic Balance. The trial value of Dvg corresponding to the best agreement was treated as its experimental value. By reviewing and regression fitting of all available experimental data, an improved expression of Dvg is proposed. The accuracy is evaluated to be ± 4 % in the temperature range of 248 K to 600 K.

Mass accommodation and gas–particle partitioning in secondary organic aerosols: dependence on diffusivity, volatility, particle-phase reactions, and penetration depth

Abstract. Mass accommodation is an essential process for gas–particle partitioning of organic compounds in secondary organic aerosols (SOA). The mass accommodation coefficient is commonly described as the probability of a gas molecule colliding with the surface to enter the particle phase. It is often applied, however, without specifying if and how deep a molecule has to penetrate beneath the surface to be regarded as being incorporated into the condensed phase (adsorption vs. absorption). While this aspect is usually not critical for liquid particles with rapid surface–bulk exchange, it can be important for viscous semi-solid or glassy solid particles to distinguish and resolve the kinetics of accommodation at the surface, transfer across the gas–particle interface, and further transport into the particle bulk. For this purpose, we introduce a novel parameter: an effective mass accommodation coefficient αeff that depends on penetration depth and is a function of surface accommodation coefficient, volatility, bulk diffusivity, and particle-phase reaction rate coefficient. Application of αeff in the traditional Fuchs–Sutugin approximation of mass-transport kinetics at the gas–particle interface yields SOA partitioning results that are consistent with a detailed kinetic multilayer model (kinetic multilayer model of gas–particle interactions in aerosols and clouds, KM-GAP; Shiraiwa et al., 2012) and two-film model solutions (Model for Simulating Aerosol Interactions and Chemistry, MOSAIC; Zaveri et al., 2014) but deviate substantially from earlier modeling approaches not considering the influence of penetration depth and related parameters. For highly viscous or semi-solid particles, we show that the effective mass accommodation coefficient remains similar to the surface accommodation coefficient in the case of low-volatility compounds, whereas it can decrease by several orders of magnitude in the case of semi-volatile compounds. Such effects can explain apparent inconsistencies between earlier studies deriving mass accommodation coefficients from experimental data or from molecular dynamics simulations. Our findings challenge the approach of traditional SOA models using the Fuchs–Sutugin approximation of mass transfer kinetics with a fixed mass accommodation coefficient, regardless of particle phase state and penetration depth. The effective mass accommodation coefficient introduced in this study provides an efficient new way of accounting for the influence of volatility, diffusivity, and particle-phase reactions on SOA partitioning in process models as well as in regional and global air quality models. While kinetic limitations may not be critical for partitioning into liquid SOA particles in the planetary boundary layer (PBL), the effects are likely important for amorphous semi-solid or glassy SOA in the free and upper troposphere (FT–UT) as well as in the PBL at low relative humidity and low temperature.

Drifting mass accommodation coefficients: in situ measurements from a steady state molecular dynamics setup

ABSTRACT A fundamental understanding of the evaporation/condensation phenomena is vital to many fields of science and engineering, yet there is many discrepancies in the usage of phase-change models and associated coefficients. First, a brief review of the kinetic theory of phase change is provided, and the mass accommodation coefficient (MAC, ) and its inconsistent definitions are discussed. The discussion focuses on the departure from equilibrium; represented as a macroscopic “drift” velocity. Then, a continuous flow, phase change driven molecular-dynamics setup is used to investigate steady-state condensation at a flat liquid-vapor interface of argon at various phase-change rates and temperatures to elucidate the effect of equilibrium departure. MAC is computed directly from the kinetic theory-based Hertz–Knudsen (H-K) and Schrage (exact and approximate) expressions without the need for a priori physical definitions, ad-hoc particle injection/removal, or particle counting. MAC values determined from the approximate and exact Schrage expressions ( and ) are between 0.8 and 0.9, while MAC values from the H-K expression () are above unity for all cases tested. yield value closest to the results from transition state theory [J Chem Phys, 118, 1392–1399 (2003)]. The departure from equilibrium does not affect the value of but causes to vary drastically emphasizing the importance of a drift velocity correction. Additionally, equilibrium departure causes a nonuniform distribution in vapor properties. At the condensing interface, a local rise in vapor temperature and a drop in vapor density is observed when compared with the corresponding bulk values. When the deviation from bulk values are taken into account, all values of MAC including show a small yet noticeable difference that is both temperature and phase-change rate dependent.

Investigating the validity of Schrage relationships for water using molecular dynamics simulations.

Recently, molecular dynamics (MD) simulations were utilized to show that Schrage theory predicts evaporation/condensation mass fluxes with good accuracy in the case of monoatomic and non-polar molecular fluids. Here, we examine if they are equally accurate for molecular polar fluids, such as water. In particular, using molecular dynamics (MD) simulations, we study the steady state evaporation/condensation processes of water in a one-dimensional heat-pipe geometry to ascertain the validity of Schrage relationships. Non-equilibrium mass flow is driven by controlling the temperatures of the source/sink. Equilibrium simulations are utilized to evaluate the saturation properties and the mass accommodation coefficients as a function of temperature. Our results indicate that Schrage equations predict the evaporation/condensation rates of water with good accuracy. Moreover, we show that molecular velocity distributions in the vapor phase are indeed Maxwellian distributions shifted by the velocity of the macroscopic vapor flow, as assumed in Schrage's theoretical analysis.

Correction to “Mass Accommodation Coefficients of Water on Organics from Complementary Photoacoustic and Light Scattering Measurements on Laser-Trapped Droplets”

Correction to “Mass Accommodation Coefficients of Water on Organics from Complementary Photoacoustic and Light Scattering Measurements on Laser-Trapped Droplets”

Correction: Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles.

Correction for 'Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles' by Matus E. Diveky et al., Phys. Chem. Chem. Phys., 2019, 21, 4721-4731, DOI: .

Mass Accommodation Coefficients of Water on Organics from Complementary Photoacoustic and Light Scattering Measurements on Laser-Trapped Droplets

The mass accommodation coefficient, $\alpha_M$, describes evaporation and condensation kinetics at the liquid-vapor interface. In spite of numerous experimental efforts, reliable values of $\alpha_M$ are still not available for many substances. Here, we present a novel experimental technique, photothermal single-particle spectroscopy (PSPS), that allows for a robust retrieval of mass accommodation coefficients from three simultaneous independent measurements. PSPS combines resonant photoacoustic absorption spectroscopy with modulated Mie scattering measurements on single particles. We study the mass transport of water on organic aerosol droplets that are optically trapped using counter-propagating tweezers. We find the mass accommodation coefficient of water on a pure model organic that is fully miscible with water to be 0.021 at 296K, and to decrease by more than an order of magnitude when the temperature increases to 309K. The experimentally observed temperature dependence of $\alpha_M$ shows an Arrheni...

Transport phenomena in the Knudsen layer near an evaporating surface.

Using the combination of the kinetic theory of gases (KTG), Boltzmann transport equation (BTE), and molecular dynamics (MD) simulations, we study the transport phenomena in the Knudsen layer near a planar evaporating surface. The MD simulation is first used to validate the assumption regarding the anisotropic velocity distribution of vapor molecules in the Knudsen layer. Based on this assumption, we use the KTG to formulate the temperature and density of vapor at the evaporating surface as a function of the evaporation rate and the mass accommodation coefficient (MAC), and we use these vapor properties as the boundary conditions to find the solution to the BTE for the anisotropic vapor flow in the Knudsen layer. From the study of the evaporation into a vacuum, we show the ratio of the macroscopic speed of vapor to the most probable thermal speed of vapor molecules in the flow direction will always reach the maximum value of sqrt[1.5] at the vacuum boundary. The BTE solutions predict that the maximum evaporation flux from a liquid surface at a given temperature depends on both the MAC and the distance between the evaporating surface and the vacuum boundary. From the study of the evaporation and condensation between two parallel plates, we show the BTE solutions give good predictions of transport phenomena in both the anisotropic vapor flow within the Knudsen layer and the isotropic flow out of the Knudsen layer. All the predictions from the BTE are verified by the MD simulation results.

Direct measurements of semi-volatile organic compound dynamics show near-unity mass accommodation coefficients for diverse aerosols

The partitioning of low- and semi-volatile organic compounds into and out of particles significantly influences secondary organic aerosol formation and evolution. Most atmospheric models treat partitioning as an equilibrium between gas and particle phases, despite few direct measurements and a large range of uncertain mass accommodation coefficients (α). Here we directly measure the dynamic, isothermal partitioning of specific organic compounds using mass spectrometry in a Teflon chamber. Measurements are conducted under dry and humid conditions using seeds of different properties that are atmospherically relevant. α values determined independently from gas- and particle-phase observations are consistent and average 0.88 ± 0.33 for all the studied seeds and probe gases. Our results also imply fast mixing, within ~200 s, between dry α-pinene/O3 SOA and the oxidized compounds. These results indicate that mass transfer limitations in the atmosphere may be less important than some recent studies suggest.

Dynamic method to measure partition coefficient and mass accommodation coefficient for gas‒particle interaction of phthalates

The particle-gas partition coefficient (Kp) and mass accommodation coefficient (α) are two parameters characterizing the gas-particle interaction of semi-volatile organic compounds (SVOCs). Most of the available methods for measuring Kp require equilibrium at the chamber outlet, implying substantial preliminary testing. The need to separate gas-phase and particle-phase SVOCs also reduces the method accuracy. Few studies measuring α for indoor-related SVOCs are available, and they usually ignore the wall loss of SVOCs, resulting in reduced measurement accuracy. To overcome these deficiencies, we developed a dynamic method coupling a laminar flow tube chamber and an SVOC mass transfer model. Using the interaction between gas-phase di-2-ethylhexyl phthalate (DEHP) and (NH4)2SO4 particles (with diameters in the range of 10–600 nm) as an example, experiments were performed to evaluate the effectiveness and accuracy of the dynamic method. For the experimental conditions investigated (temperature = 25 °C and relative humidity <10%), gas-particle interaction between DEHP and (NH4)2SO4 particles is governed by surface adsorption because (NH4)2SO4 particles are in solid state. In this case, gas-particle partitioning should be characterized by the surface-area-normalized partition coefficient (KpA). KpA and α were measured to be 260 ± 80 m and 0.20 ± 0.05, respectively. Both are consistent with results reported in the literature. The method applicability for other SVOC-particle combinations and the improvement of method accuracy require further study.Copyright © 2019 American Association for Aerosol Research

Theoretical evaluation of different factors affecting the HO2 uptake coefficient driven by aqueous-phase first-order loss reaction

The heterogeneous loss on aerosols is an important sink of HO2, affecting the radical chemistry and cycling, and thus it plays a key role in the atmospheric photochemistry. Gaining a reasonable HO2 uptake coefficient (γHO2) would be of great importance in evaluating the heterogeneous loss rate of HO2 on aerosols. This work was motivated by the large variance of reported HO2 mass accommodation coefficients (αHO2) in laboratory studies (0.1–1), which can cause consequent bias in the parameterized HO2 uptake coefficient (γHO2). We conducted a theoretical analysis of the roles of several key factors or parameters in determining γHO2 on a sphere droplet with adjustable Cu2+ ion concentration including αHO2, aqueous-phase acidity, the first-order loss-rate constant KI value, and the aqueous phase production of HO2. The results intuitively demonstrate that utilizing a single γHO2 value for aerosols of different sizes, compositions or hygroscopic states is unsafe in atmospheric models. The theoretical analysis indicated that for a single aerosol experiencing hygroscopic growth, γHO2 decreased with increasing aerosol size, because of the increased gas phase diffusion resistance and dilution of aqueous-phase HO2 consuming ions. Aerosol pH and metal abundance influence γHO2 by determining the aqueous-phase loss-rate constants, and these two factors were found to be only predominant for large particles/droplets (Rp > 1 μm). For small and middle size aerosols, the mass accommodation process plays the determining role in controlling HO2 uptake. Considering ambient aerosols rarely grow to cloud droplet size on sunny days when photochemical budget of HO2 radicals is of more concern, it is crucial to adopt appropriate αHO2 in models, as arbitrarily choosing the αHO2 value can lead to large bias when simulating HO2 heterogeneous process on ambient aerosols.

Mass accommodation at a high-velocity water liquid-vapor interface

We use molecular dynamics to determine the mass accommodation coefficient (MAC) of water vapor molecules colliding with a rapidly moving liquid-vapor interface. This interface mimics those present in collapsing vapor bubbles that are characterized by large interfacial velocities. We find that at room temperature, the MAC is generally close to unity, and even with interfaces moving at 10 km/s velocity, it has a large value of 0.79. Using a simplified atomistic fluid model, we explore the consequences of vapor molecule interfacial collision rules on pressure, temperature, and density of a vapor subjected to an incoming high-velocity liquid-vapor interface.

Curvature Dependence of the Mass Accommodation Coefficient.

Mass accommodation coefficient, a parameter that captures molecular transport phenomena at liquid-vapor interfaces, is essential for predicting the growth of liquid droplets during condensation processes but is difficult to obtain experimentally. Molecular simulations have been widely used to obtain accommodation coefficients for planar interfaces, but the applicability of planar accommodation coefficients to the high-curvature interfaces present in very small droplets is not clear. In this work, molecular dynamics simulations are used to compute equilibrium mass accommodation coefficients at different temperatures for small droplets of various fluids, including Lennard-Jones and Buckingham fluids, benzene, butane, methane, methanol, and water. For all fluids studied, the mass accommodation coefficient increases with droplet size to a constant limiting value and decreases with temperature. Furthermore, the accommodation coefficient curvature dependence collapses onto a universal curve when appropriately scaled.

Assessing relative humidity dependent photoacoustics to retrieve mass accommodation coefficients of single optically trapped aerosol particles.

Photoacoustic spectroscopy is widely used to measure the light absorption of aerosols. However, the impact of key factors such as the effect of relative humidity and mass exchange on photoacoustic measurements are still poorly understood. We assess such measurement biases and their physical origin by analysing the photoacoustic signal of single tetraethylene glycol (TEG) particles at varying relative humidities. Our results show a decrease in the photoacoustic signal at elevated relative humidities for small particles (0.8-1.5 μm), while for larger sizes (2.2-3.2 μm) the trend is reversed. We model the photoacoustic signal to interpret the observed behaviour in terms of mass and heat flux contribution. The single particle photoacoustic signal analysis presented in this paper additionally allows for the retrieval of the mass accommodation coefficient. Fitting our experimental data to the theoretical model reveals values of αM ≈ 0.02-0.005 for water on TEG in the temperature range 295-309 K.

The influence of particle composition upon the evolution of urban ultrafine diesel particles on the neighbourhood scale

Abstract. A recent study demonstrated that diesel particles in urban air undergo evaporative shrinkage when advected to a cleaner atmosphere (Harrison et al., 2016). We explore, in a structured and systematic way, the sensitivity of nucleation-mode diesel particles (diameter &lt; 30 nm) to changes in particle composition, saturation vapour pressure, and the mass accommodation coefficient. We use a multicomponent aerosol microphysics model based on surrogate molecule (C16−C32 n-alkane) volatilities. For standard atmospheric conditions (298 K, 1013.25 hPa), and over timescales (ca. 100 s) relevant for dispersion on the neighbourhood scale (up to 1 km), the choice of a particular vapour pressure dataset changes the range of compounds that are appreciably volatile by two to six carbon numbers. The nucleation-mode peak diameter, after 100 s of model runtime, is sensitive to the vapour pressure parameterisations for particles with compositions centred on surrogate molecules between C22H46 and C24H50. The vapour pressure range, derived from published data, is between 9.23 × 10−3 and 8.94 × 10−6 Pa for C22H46 and between 2.26 × 10−3 and 2.46 × 10−7 Pa for C24H50. Therefore, the vapour pressures of components in this range are critical for the modelling of nucleation-mode aerosol dynamics on the neighbourhood scale and need to be better constrained. Laboratory studies have shown this carbon number fraction to derive predominantly from engine lubricating oil. The accuracy of vapour pressure data for other (more and less volatile) components from laboratory experiments is less critical. The influence of a core of non-volatile material is also considered; non-volatile core fractions of more than 5 % are inconsistent with the field measurements that we test the model against. We consider mass accommodation coefficient values less than unity and find that model runs with more volatile vapour pressure parameterisations and lower accommodation coefficients are similar to runs with less volatile vapour pressure parameterisations and higher accommodation coefficients. The new findings of this study may also be used to identify semi-volatile organic compound (SVOC) compositions that play dominating roles in the evaporative shrinkage of the nucleation mode observed in field measurements (Dall'Osto et al., 2011).

A model framework to retrieve thermodynamic and kinetic properties of organic aerosol from composition-resolved thermal desorption measurements

Abstract. Chemical ionization mass spectrometer (CIMS) techniques have been developed that allow for quantitative and composition-resolved measurements of organic compounds as they desorb from secondary organic aerosol (SOA) particles, in particular during their heat-induced evaporation. One such technique employs the Filter Inlet for Gases and AEROsol (FIGAERO). Here, we present a newly developed model framework with the main aim of reproducing FIGAERO-CIMS thermograms: signal vs. ramped desorption temperature. The model simulates the desorption of organic compounds during controlled heating of filter-sampled SOA particles, plus the subsequent transport of these compounds through the FIGAERO manifold into an iodide-CIMS. Desorption is described by a modified Hertz–Knudsen equation and controlled chiefly by the temperature-dependent saturation concentration C*, mass accommodation (evaporation) coefficient, and particle surface area. Subsequent transport is governed by interactions with filter and manifold surfaces. Reversible accretion reactions (oligomer formation and decomposition) and thermal decomposition are formally described following the Arrhenius relation. We use calibration experiments to tune instrument-specific parameters and then apply the model to a test case: measurements of SOA generated from dark ozonolysis of α-pinene. We then discuss the ability of the model to describe thermograms from simple calibration experiments and from complex SOA, and the associated implications for the chemical and physical properties of the SOA. For major individual compositions observed in our SOA test case (#C=8 to 10), the thermogram peaks can typically be described by assigning C25∘C* values in the range 0.05 to 5 µg m−3, leaving the larger, high-temperature fractions (&gt;50 %) of the thermograms to be described by thermal decomposition, with dissociation rates on the order of ∼1 h−1 at 25 ∘C. We conclude with specific experimental designs to better constrain instrumental model parameters and to aid in resolving remaining ambiguities in the interpretation of more complex SOA thermogram behaviors. The model allows retrieval of quantitative volatility and mass transport information from FIGAERO thermograms, and for examining the effects of various environmental or chemical conditions on such properties.

Studying volatility from composition, dilution, and heating measurements of secondary organic aerosols formed during &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-pinene ozonolysis

Abstract. Traditional yield curve analysis shows that semi-volatile organic compounds are a major component of secondary organic aerosols (SOAs). We investigated the volatility distribution of SOAs from α-pinene ozonolysis using positive electrospray ionization mass analysis and dilution- and heat-induced evaporation measurements. Laboratory chamber experiments were conducted on α-pinene ozonolysis, in the presence and absence of OH scavengers. Among these, we identified not only semi-volatile products, but also less volatile highly oxygenated molecules (HOMs) and dimers. Ozonolysis products were further exposed to OH radicals to check the effects of photochemical aging. HOMs were also formed during OH-initiated photochemical aging. Most HOMs that formed from ozonolysis and photochemical aging had 10 or fewer carbons. SOA particle evaporation after instantaneous dilution was measured at &lt; 1 and ∼ 40 % relative humidity. The volume fraction remaining of SOAs decreased with time and the equilibration timescale was determined to be 24–46 min for SOA evaporation. The experimental results of the equilibration timescale can be explained when the mass accommodation coefficient is assumed to be 0.1, suggesting that the existence of low-volatility materials in SOAs, kinetic inhibition, or some combined effect may affect the equilibration timescale measured in this study.

Mass accommodation coefficients of fresh and aged biomass-burning emissions

ABSTRACTMost chemical transport models treat the partitioning of semi-volatile organic compounds (SVOCs) with the assumption of instantaneous thermodynamic equilibrium. However, the mass accommodation coefficients, α, of biomass-burning organic aerosol (BBOA) are largely unconstrained. During the FLAME-IV campaign, we thermally perturbed aged and fresh BBOA with a variable residence time thermodenuder and measured the resulting change in particle mass concentration to restore equilibrium. We used this equilibration profile to retrieve an effective α for components of BBOA that dictated this profile and found that the mass accommodation coefficients lie within the range 0.1 ≪ α ⩽ 1. A simple plume dilution model shows a maximum of only a 7% difference between a dynamical and an instantaneous equilibrium partitioning model using our best-estimate value for α. This supports continued use of the equilibrium assumption to treat partitioning of biomass-burning emissions in chemical-transport models.Copyright © ...

A reference data set for validating vapor pressure measurement techniques: homologous series of polyethylene glycols

Abstract. To predict atmospheric partitioning of organic compounds between gas and aerosol particle phase based on explicit models for gas phase chemistry, saturation vapor pressures of the compounds need to be estimated. Estimation methods based on functional group contributions require training sets of compounds with well-established saturation vapor pressures. However, vapor pressures of semivolatile and low-volatility organic molecules at atmospheric temperatures reported in the literature often differ by several orders of magnitude between measurement techniques. These discrepancies exceed the stated uncertainty of each technique which is generally reported to be smaller than a factor of 2. At present, there is no general reference technique for measuring saturation vapor pressures of atmospherically relevant compounds with low vapor pressures at atmospheric temperatures. To address this problem, we measured vapor pressures with different techniques over a wide temperature range for intercomparison and to establish a reliable training set. We determined saturation vapor pressures for the homologous series of polyethylene glycols (H − (O − CH2 − CH2)n − OH) for n = 3 to n = 8 ranging in vapor pressure at 298 K from 10−7 to 5×10−2 Pa and compare them with quantum chemistry calculations. Such a homologous series provides a reference set that covers several orders of magnitude in saturation vapor pressure, allowing a critical assessment of the lower limits of detection of vapor pressures for the different techniques as well as permitting the identification of potential sources of systematic error. Also, internal consistency within the series allows outlying data to be rejected more easily. Most of the measured vapor pressures agreed within the stated uncertainty range. Deviations mostly occurred for vapor pressure values approaching the lower detection limit of a technique. The good agreement between the measurement techniques (some of which are sensitive to the mass accommodation coefficient and some not) suggests that the mass accommodation coefficients of the studied compounds are close to unity. The quantum chemistry calculations were about 1 order of magnitude higher than the measurements. We find that extrapolation of vapor pressures from elevated to atmospheric temperatures is permissible over a range of about 100 K for these compounds, suggesting that measurements should be performed best at temperatures yielding the highest-accuracy data, allowing subsequent extrapolation to atmospheric temperatures.