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Simplifying assumptions

MAM4 treats the condensation and evaporation of two chemical gases: sulfuric acid (\({\rm H_2SO_4}\)) and a single lumped semi-volatile organic gas-phase species referred to as SOAG. (MAM7 also treats condensation of ammonia, \(\rm NH_3\)).

Here we first introduce a set of key assumptions used in MAM's gas-aerosol mass exchange parameterizations.

  • In the tropospheric configuration of MAM, sulfric acid is an nonvolatile species.

  • The mass transfer coefficient of sulfric acid is calculated for each aerosol mode by taking into account the lognormal size distribution. The mass transfer coefficients of other species are assumed to be propotional to that of sulfric acid. For example, the transfer coefficient of SOA is assumed to be 0.81 of that of sulfric acid.

  • For any condensable gas species, it is assumed that the equilibrium (saturation) vapor concentration just above the surface of an aerosol particle, i.e., the \(\widetilde{c}_{L,sat}\) defined in the section on mass transfer rates, is independent of particle size within a lognormal mode but can vary from mode to mode, in time, and in space.

In addition, there are various more detailed assumptions use for the gas-aerosol mass transfer of SOA. These are explained in the section on the time evolution equations for SOA

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