Parameterizations for calculating the equilibrium vapor pressure of the semivolatile inorganic gases, HNO(3), HCl, and NH(3), above an aqueous aerosol are presented. The hybrid Partial Derivative Fitted Taylor Expansion (PD-FiTE) approach uses optimized model parameters describing the interaction between different inorganic ions, resulting in comparable computational performance with existing reduced methods while remaining accurate. Comparisons with the most accurate inorganic activity coefficient model available indicate that PD-FiTE performs very well over the parameterization space of the system H(+)-NH(4)(+)-Na(+)-SO(4)(2-)-HSO(4)(-)-NO(3)(-)-Cl(-) at 298.15 K. The linear additive framework allows the inclusion of further species. However, including the ability to describe the interaction between inorganic and organic components will be presented in a future publication. Coupling PD-FiTE to a coupled box model of gaseous chemistry and aerosol microphysics in a test case investigating marine aerosol passing through a polluted environment demonstrates its robustness and ability to capture fine details of important phenomena such as the outgassing of HCl in response to HNO(3) uptake by sea-salt particles.