Abstract
Abstract. We present EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting for Temperature, Intramolecular, and Non-additivity effects), a method to predict (subcooled) liquid pure compound vapour pressure p0 of organic molecules that requires only molecular structure as input. The method is applicable to zero-, mono- and polyfunctional molecules. A simple formula to describe log10p0(T) is employed, that takes into account both a wide temperature dependence and the non-additivity of functional groups. In order to match the recent data on functionalised diacids an empirical modification to the method was introduced. Contributions due to carbon skeleton, functional groups, and intramolecular interaction between groups are included. Molecules typically originating from oxidation of biogenic molecules are within the scope of this method: aldehydes, ketones, alcohols, ethers, esters, nitrates, acids, peroxides, hydroperoxides, peroxy acyl nitrates and peracids. Therefore the method is especially suited to describe compounds forming secondary organic aerosol (SOA).
Highlights
The liquid pure compound vapour pressure p0 of a molecule is an important property influencing its distribution between the gas and particulate phase
These semi- and lowvolatility molecules originate from the oxidation of volatile organic compound (VOC) and they are of such a large diversity that a full determination of all species is unrealistic, let alone that for each species a vapour pressure can be measured
Used is the equilibrium partitioning formalism proposed by Pankow (1994) where the organic aerosol is considered as a well-mixed liquid; recent findings (Cappa and Wilson, 2011) suggest that another mechanism is possible, where the aerosol is rapidly converted from an absorptive to a non-absorptive phase
Summary
The (subcooled) liquid pure compound vapour pressure p0 of a molecule is an important property influencing its distribution between the gas and particulate phase. For low-volatility compounds, the method of Joback and Reid (1987) overpredicts boiling points (Stein and Brown, 1994; Barley and McFiggans, 2010; Compernolle et al, 2010), and the method of Myrdal and Yalkowsky (1997) tends to overestimate vapour pressures (Barley and McFiggans, 2010) when provided with an experimental boiling point Another frequently encountered limitation is that not all molecule types are covered by the method at hand. Recently new room temperature low vapour pressure data of polyfunctional compounds became available – especially diacids and polyfunctional diacids (Frosch et al, 2010; Booth et al, 2010, 2011) – and it turned out that the available methods do not predict this data well (Booth et al, 2010, 2011) For these reasons, a new estimation method addressing the above issues is desirable
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