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

Abstract

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−CH 2 −CH 2 ) 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.

Optimization of process models for determining volatility distribution and viscosity of organic aerosols from isothermal particle evaporation data

“…Once trapped, a single particle sits in a nitrogen flow (200 mL min −1 , gas flow velocity of 3 cm s −1 ) of controlled RH and T . The RH is measured by fitting either the size vs. time profile of an evaporating probe water droplet (at RHs above 80 %) or the equilibrated radius of a NaCl or NaNO 3 aqueous solution probe droplet (below 80 %) by applying a literature evaporation-condensation kinetic model (Kulmala et al, 1993). The procedure is described in Rovelli et al (2016), where the uncertainties associated with the measured RH are also discussed (typically < ±0.2 % at RH > 90 % and ∼ ±1 % below 90 %).…”

Estimating the saturation vapor pressures of isoprene oxidation products C&lt;sub&gt;5&lt;/sub&gt;H&lt;sub&gt;12&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; and C&lt;sub&gt;5&lt;/sub&gt;H&lt;sub&gt;10&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; using COSMO-RS

“…Based on the limited number of direct comparisons between predicted and experimental data, and further assuming that the effect is roughly proportional to the maximum number of intramolecular H-bonds, the overestimation seems to be on the order of a factor of 5 per H-bond. If applied to the data in Kurtén et al (2016) on monoterpene autoxidation products, this would imply that the originally suggested approach of taking the geometric average of SIMPOL and COSMOtherm saturation vapor pressure predictions remains a reasonably good choice in the absence of other information. While COSMOtherm saturation vapor pressure predictions can be modified to agree better with experiments by scaling the hydrogen bond enthalpy parameter c1, the optimal value for this parameter is likely to depend on the system, and this approach can thus not generally be recommended.…”

A method for extracting calibrated volatility information from the FIGAERO-HR-ToF-CIMS and its application to chamber and field studies

“…CC BY 4.0 License. measured at room temperature, demonstrating their thermal stability (Krieger et al, 2018). The stability of the PEG compounds allowed samples to be shared between the co-authors of Krieger et al, (2018), ensuring sample conformity.…”

“…The vapour pressure of the Polyethylene glycol (PEG) series, as described in the Krieger et al, (2018) study, were measured by multiple techniques; KEMS (Booth et al, 2009), electrodynamic balance instruments (Zardini et al, 2006;Rovelli et al, 2016) and Tandem Differential Mobility Analyser (TDMA) including a laminar flow tube (Bilde et al, 2003)).…”