SIMPOL phase transfer reactions are based on the SIMPOL.1 model calculations of vapor pressure described by Pankow and Asher (2008) [Pankow2008].

Mass accomodation coefficients and condensation rate constants are calculated using the method of Ervans et al. (2003) [Ervens2003] and references therein. Mass accomodation coefficients ( \(\alpha\)) are calculated as:

\[ \Delta H_{obs} = -10 \times (N^*-1) + 7.53 \times (N^{*2/3}-1) - 0.1 \times 10 \quad (\mbox{kcal}\,\mbox{M}^{-1}) \]

\[ \Delta S_{obs} = -13 \times (N^*-1) - 19 \times (N^*-1) + 9.21 \times (N^{*2/3}-1) - 0.1 \times 13 \quad (\mbox{cal}\,\mbox{M}^{-1}\,\mbox{K}^{-1}) \]

\[ \frac{\alpha}{1-\alpha} = e^{\frac{-\Delta G^{*}}{RT}} \]

If \(\Delta H\) and \(\Delta S\) are not provided, the mass accomodation coefficient is assumed to be 0.1 ([Zaveri2008]).

Condensation rate constants are calculated following [Zaveri2008] as:

\[ k_c = 4 \pi r D_g f_{fs}( K_n, \alpha ) \]

where \(r\) is the radius of the particle(s) [m], \(D_g\) is the diffusion coefficient of the gas-phase species [ \(\mbox{m}^2\,\mbox{s}^{-1}\)], \(f_{fs}( K_n, \alpha )\) is the Fuchs Sutugin transition regime correction factor [unitless], \(K_n\) is the Knudsen Number [unitess], and \(\alpha\) is the mass accomodation coefficient.

Rates can be calculated as:

\[ r_c = [G] N_a k_c \]

where \([G]\) is the gas-phase species concentration [ppm], \(N_a\) is the number concentration of particles [ \(\mbox{particle}\,\mbox{m}^{-3}\)] and the rate \(r_c\) is in [ \(\mbox{ppm}\,\mbox{s}^{-1}\)]. The particle radius used to calculate \(k_{f}\) is the effective radius [ \(r_{eff}\)], which is taken as the "least-wrong" choice for condensation rates, as it is weighted to surface area [Zender2002] .

Input data for SIMPOL phase transfer reactions have the following format :

{
  "type" : "SIMPOL_PHASE_TRANSFER",
  "gas-phase species" : "my gas spec",
  "aerosol phase" : "my aero phase",
  "aerosol-phase species" : "my aero spec",
  "aerosol-phase activity coefficient" : "my aero act coeff"
  "B" : [ 123.2e3, -41.24, 2951.2, -1.245e-4 ]
    ...
}

The key-value pairs gas-phase species, aerosol phase and aerosol-phase species are required. Only one gas- and one aerosol-phase species are allowed per phase-transfer reaction. The key-value pair aerosol-phase activity coefficient is optional. When it is included its value must be the name of an species of type ACTIVITY_COEFF that is present in the specified aerosol phase. When it is not included, activity coefficients are assume to be 1.0.

Gas-phase species must include parameters named diffusion coeff [m2 s-1], which specifies the diffusion coefficient in \(\mbox{m}^2\,\mbox{s}^{-1}\), and molecular weight [kg mol-1], which specifies the molecular weight of the species in \(\mbox{kg}\,\mbox{mol}^{-1}\). They may optionally include the parameter N star, which will be used to calculate th mass accomodation coefficient. When this parameter is not included, the mass accomodation coefficient is assumed to be 1.0.

The key-value pair B is also required and must have a value of an array of exactly four members that specifies the SIMPOL parameters for the partitioning species. The B parameters can be obtained by summing the contributions of each functional group present in the partitioning species to the overall \(B_{n,i}\) for species \(i\), such that:

\[ B_{n,i} = \sum_{k} \nu_{k,i} B_{n,k} \forall n \in [1...4] \]

where \(\nu_{k,i}\) is the number of functional groups \(k\) in species \(i\) and the parameters \(B_{n,k}\) for each functional group \(k\) can be found in table 5 of Pankow and Asher (2008) [Pankow2008].