The original APES effects a Duffing attempt to split the non-diffusive correction from the correction for the diffusive mass transfer. The Duffing approach was to use the Poison distribution to represent the density of the PMP and the passive fraction as the volume of the density pellet. Non-diffusive mass transfer was then represented as a correction to this passive fraction. In the Pika code, the correction for the non-diffusive component was retained, but the concentration and pH correction for the diffusive component was dropped. This is what reduces the mass transfer correction from % to ppm. It would be possible to focus only on the non-diffusive instead of including both, however, this formulation allows for arbitrary mass transfer correction to be applied.
The calculation of the solution pH by Pika does NOT work for ions that do not share a proton among a family of similar ions. These include the most important ions that are available, i.e. Br-HBr, Br-ClBr, Br-SCN, Br-DMSO, Br-COOH, Br-COODMP, etc, Cl-ClCl, Cl-ClCl+, Cl-DMSO, Cl-COODMP, Cl-COOCH3, etc. In the Pika code, the acid dissociation constants were used, with some modification, to mitigate the problem. No explicit pH corrections were made. In the original APES, these corrections were made for the concentrations or solutions pH, and these still apply.
This code assumes that the gas molecules are interacting with the solid. Typically, the solid surface is formed by condensation of aerosol particles. However, some experiments and calculations will ignore this surface in favor of the gas/gas interaction. For example, some aerosol gas mixture interaction papers only consider the gas-gas interaction, whereas all the H/C/N/etc oxidized compounds are produced in the aerosol complex and can be found in the vapor phase as well. Furthermore, some experiments are done in sealed vials. In these cases, the produced aerosols are directly into the gas phase without an aerosol-solid interaction. d2c66b5586