SIMPOL.1: A simple group contribution method for predicting vapor pressures and enthalpies of vaporization of multifunctional organic compounds

Abstract

Abstract. The SIMPOL.1 group contribution method is developed for predicting the liquid vapor pressure pLo (atm) and enthalpy of vaporization ΔHvap (kJ mol-1) of organic compounds as functions of temperature (T). For each compound i, the method assumes log10pL,io(T)=Σkνk,ibk(T) where νk,i is the number of groups of type k, and bk(T) is the contribution to log10 pL,io(T) by each group of type k. A zeroeth group is included that uses b0(T) with ν0,i=1 for all i. A total of 30 structural groups are considered: molecular carbon, alkyl hydroxyl, aromatic hydroxyl, alkyl ether, alkyl ring ether, aromatic ether, aldehyde, ketone, carboxylic acid, ester, nitrate, nitro, alkyl amine (primary, secondary, and tertiary), aromatic amine, amide (primary, secondary, and tertiary), peroxide, hydroperoxide, peroxy acid, C=C, carbonylperoxynitrate, nitro-phenol, nitro-ester, aromatic rings, non-aromatic rings, C=C–C=O in a non-aromatic ring, and carbon on the acid-side of an amide. The T dependence in each of the bk(T) is assumed to follow b(T)=B1/T+B2+B3T+B4lnT. Values of the B coefficients are fit using an initial basis set of 272 compounds for which experimentally based functions pL,io=fi(T) are available. The range of vapor pressure considered spans fourteen orders of magnitude. The ability of the initially fitted B coefficients to predict pLo values is examined using a test set of 161 compounds and a T range that is as wide as 273.15 to 393.15 K for some compounds. σFIT is defined as the average over all points of the absolute value of the difference between experimental and predicted values of log10pL,io(T). After consideration of σFIT for the test set, the initial basis set and test set compounds are combined, and the B coefficients re-optimized. For all compounds and temperatures, σFIT=0.34: on average, pL,io(T) values are predicted to within a factor of 2. Because d(log10pL,io(T))/d(1/T) is related to the enthalpy of vaporization ΔHvap,i, the fitted B provide predictions of ΔHvap,i based on structure.

Chemistry of Secondary Organic Aerosol Formation from OH Radical-Initiated Reactions of Linear, Branched, and Cyclic Alkanes in the Presence of NOx

“…The order of T des of these compounds is consistent with the expected reductions in vapor pressures due to the addition of functional groups (Pankow and Asher 2008): hydroxy + nitrate > hydroxy ∼ = nitrate > carbonyl + ester. AN-N, which would be expected to desorb close to 1,4HN, were not assigned a T des because the potential characteristic ions could also be explained as coming from other, more abundant products.…”

“…• C), since hydroxy and nitrate groups reduce vapor pressure more than carbonyl groups (Pankow and Asher 2008). The addition of NH 3 also led to the disappearance of peaks at 86, 94, and 98…”

“…The second general principle is that compound vapor pressures decrease as the number of functional groups increase, leading to the expectation that more functionalized products will desorb at higher temperatures. For the functional groups expected to be present in the products of alkane reactions, hydroxy and nitrate (also called nitrooxy) groups should reduce vapor pressures and therefore increase T des more than carbonyls and esters (Pankow and Asher 2008). Also, for reasons that are not understood, but may involve particlephase oligomer-forming reactions, products containing a CHA structure desorb at much higher temperatures than expected on the basis of vapor pressures calculated from structure-activity relationships (Jordan et al 2008).…”

Formation of Low Volatility Organic Compounds and Secondary Organic Aerosol from Isoprene Hydroxyhydroperoxide Low-NO Oxidation

“…Note that the noncondensing isomer may be lost to the inlet less efficiently than the condensing isomer, and thus may have an overestimated concentration, but this is of no consequence for the SOA modeling. 32 Contributions are listed from: "N c ", the number of carbon atoms; "C=O", ketones and aldehydes; "OH," hydroxyl groups; "COOH," carboxylic acids; "OOH," hydroperoxyl groups; "CO(O)OH," peroxy acids; and "C=C," carbon-carbon double bonds. The impact of C* of aldehydes and ketones are only slightly different, so they were grouped together here for simplicity.…”

Effect of the OH Radical Scavenger Hydrogen Peroxide on Secondary Organic Aerosol Formation from α-Pinene Ozonolysis

“…Under these low-NO x conditions, the HO 2 radicals will react with RO 2 radicals from the α-pinene ozonolysis reaction to produce peroxides. The difference in yields for the various scavengers is very pronounced at the C * = 100 µg m −3 bin, which is the general range of volatility one would predict for multifunctional hydroperoxides formed from α-pinene (Pankow and Asher 2008). Given the consistency of yields at low C OA (<10 µg m −3 ), we hypothesize that some more volatile products formed from RO 2 + RO 2 reactions are instead directed to less volatile hydroperoxides with enhanced HO 2 levels.…”