A group contribution method for estimating the vapour pressures of α-pinene oxidation products

[摘要] A prediction method based on group contribution principles isproposed for estimating the vapour pressure of α-pineneoxidation products.Temperature dependent contributions areprovided for the following chemical groups: carbonyl, nitrate,hydroxy, hydroperoxy, acyl peroxy nitrate and carboxy. On the basisof observed vapour pressure differences between isomers of diols anddinitrates, a simple refinement is introduced in the method toaccount for the influence of substitutions on the vapour pressurefor alcohols and nitrates. The vapour pressures predicted with thisnew method have been compared with the predictions from UNIFAC(Asher et al., 2002). Given the large uncertainties of the vapourpressure data for the least volatile compounds, further experimentalstudies of subcooled vapour pressures of multifunctional compoundsat ambient temperatures are required for better parameterizations.Among the α-pinene products identified to date, pinic acidand hydroxy pinonic acid are predicted to be the least volatilecompounds, with estimated vapour pressures of 3×10⁻⁶ torr and 6×10⁻⁷ torr, respectively. Thevapour pressure of the other primary products range from 10⁻⁵ to 10⁻³ torr, with hydroxy hydroperoxides presenting thelowest values. Noting that multifunctional carboxylic acids, inparticular pinic acid, are believed to be mostly present as dimersin laboratory conditions, we suggest that the partial vapourpressure of the pinic acid dimer should be close to the experimentalsubcooled vapour pressure for pinic acid (estimated at ~10⁻⁶ torr) due to its large contribution to the totalconcentration (dimer+monomer) in experimental conditions.

[学科分类] 大气科学