Global three dimensional chemically and size-resolved aerosol mass size distributions are simulated on-line in the Intermediate Model of Global Evolution of Species (IMAGES). Aerosol-phase thermodynamics is coupled to this chemical transport model using the Simulating Composition of Atmospheric Particles at Equilibrium (SCAPE2) module. Nitrate, ammonium and sulfate concentrations are calculated using an internally mixed aerosol description. Transport for both aerosol and gas-phase species is solved using a semi-Lagrangian scheme driven by monthly mean climatological variables provided by European Center for Medium-Range Weather Forecasts (ECMWF) analysis. Aerosols are removed from the atmosphere through parameterized dry and wet deposition processes. In addition to precursor gas-phase species, the thermodynamic module requires prescribed relative humidity and temperature fields updated monthly by ECMWF analysis. Comparison between calculated and observed total aerosol mass concentration fields at selected stations in North America and Europe fall within a factor of two for most species. Results suggest that aerosol distributions over continental polluted areas comprise most of the dry mass over the accumulation mode, in which sulfate appears to be the dominant ion. Although not as predominant as sulfate, nitrate seems to be of importance at least regionally in the present model.