Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 6 2005 10.5194/acpd-5-11249-2005 http://www.atmos-chem-phys-discuss.net/5/11249/2005/ http://www.atmos-chem-phys-discuss.net/5/11249/2005/acpd-5-11249-2005.html http://www.atmos-chem-phys-discuss.net/5/11249/2005/acpd-5-11249-2005.pdf 11249 11276 2005-11-03 A group contribution method for estimating the vapour pressures of α-pinene oxidation products M. Capouet manu.capouet@aeronomie.be J. F. Müller Belgian Institute for Space Aeronomy, 1180 Brussels, Belgium A prediction method based on group contribution principles is proposed for estimating the vapour pressure of α-pinene oxidation products. Temperature dependent contributions are provided for the following chemical groups: carbonyl, nitrate, hydroxy, hydroperoxide, acyl peroxy nitrate and acid. On the basis of observed vapour pressure differences between isomers of diols and dinitrates, a simple refinement is introduced in the method, which allows to account for the influence of the substitutions on the vapour pressure for the hydroxy and nitrate functionalities. In general, the predicted vapour pressures of multifunctional compounds show a better agreement with experimental data (within a factor 2–3) than the UNIFAC method (Asher et al., 2002). Among the α-pinene products identified to date, pinic acid and hydroxy pinonic acid are predicted to be the least volatile compounds, with estimated vapour pressures of 3×10^−6 torr and 6×10^−7 torr, respectively. The vapour pressure of the other primary products range from 10^−5 to 10^−3 torr, with hydroxy hydroperoxides presenting the lowest values. Noting that multifunctional carboxylic acids, in particular pinic acid, are believed to be mostly present as dimers in laboratory conditions, we suggest that the partial vapour pressure of the pinic acid dimer should be close to the experimental subcooled vapour pressure for pinic acid (estimated at ~10^−6 torr) due to its large contribution to the total concentration (dimer+monomer) in experimental conditions.