The critical assessment of vapour pressure estimation methods for use in modelling the formation of atmospheric organic aerosol

Abstract

Abstract. A selection of models for estimating vapour pressures have been tested against experimental data for a set of compounds selected for their particular relevance to the formation of atmospheric aerosol by gas-liquid partitioning. The experimental vapour pressure data (all <100 Pa) of 45 multifunctional compounds provide a stringent test of the estimation techniques, with a recent complex group contribution method providing the best overall results. The effect of errors in vapour pressures upon the formation of organic aerosol by gas-liquid partitioning in an atmospherically relevant example is also investigated. The mass of organic aerosol formed under typical atmospheric conditions was found to be very sensitive to the variation in vapour pressure values typically present when comparing estimation methods.

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

“…The sensitivities to vapour pressure are much greater than to component activity coefficient irrespective of whether the initialisations are randomly generated or predicted using a near-explicit model of oxidative VOC degradation Barley et al, 2011;Topping et al, 2011a). The sensitivities are increased when trying to represent the complex multicomponent mixture by fewer components.…”

Solid state and sub-cooled liquid vapour pressures of cyclic aliphatic dicarboxylic acids

“…Table 4 shows the two different boiling points used, the Stein and Brown (1994) boiling points are higher by 2-7 K for the cyclic compounds (excepting levoglucosan) but are lower by similar amounts for the straight chain and methyl substituted diacids. Although compared to the differences in T b values in Barley and McFiggans (2010), the differences here are quite small and the differences from the true T b are unknown. Systematic errors in T b can feed through to similar errors in vapour pressure.…”

“…Table 6 shows the estimated enthalpies of vapourisation ( H vap = H sub − H fus ) compared with those from KEMS/DSC measurements. Barley and McFiggans (2010) in their study of vapour pressure methods noted that most of the error for the methods they looked at came from the estimation of the boiling point, and slope of the vapour pressure curve (enthalpy of vapourisation) estimates were generally much easier to get right. The Moller/Nannoolal and Nannoolal/Nannoolal methods here both use the same boiling point, but for most of the compounds there is an order of magnitude difference in the predicted vapour pressure at 298 K which can only come from the difference in predicted H vap between them.…”

“…Together they described the vapour pressure from 1 atmosphere at the normal boiling point down the pressure at the required temperature, in this case 298 K. The three vapour pressure methods used are the Nannoolal et al (2008) and the Moller et al (2008) methods both with T b by Nannoolal et al (2004), and the Myrdal and Yalkowsky (1997) method with T b by Stein and Brown (1994). The methods are briefly outlined here, for more detailed descriptions see Barley and McFiggans (2010) or Booth et al (2010). The Nannoolal et al (2004) estimation method uses group contribution calculations with primary and secondary groups and group interactions (207 groups).…”

“…Here we use three methods which have previously been used in estimating vapour pressure for atmospheric compounds Booth et al, 2010). The 3 methods have been chosen as they were reported to be the best methods for a test set of 45 low volatility compounds by Barley and McFiggans (2010) and they have been used in conjunction with KEMS measurements previously (Booth et al, 2010). The vapour pressure equations (referred to here as the vapour pressure methods) describe the vapour pressure, which varies exponentially with temperature, (see Eq.…”