Modules for secondary aerosol formation included in the urban scale K-theory aerosol model, AROSOL are: An empirical first-order SO2 conversion scheme, termed EMM; The lumped parameter kinetic model termed the Carbon Bond Mechanism, in the version CBM-IV; The lumped parameter kinetic model termed the Atkinson Lloyd Mechanism, in the 1985 ERT version; The equilibrium Model for an Aerosol Reacting System (MARS) for prediction of equilibrium partition of nitrates, sulfates, and ammonium between the gas and aerosol phases; The Binary Aerosol Dynamics Model for nucleation and growth of secondary aerosol. The modules for secondary sulfate and nitrate formation have been demonstrated with data from the 1982 Philadelphia Aerosol Field Study. Both EMM and CBM give similar secondary sulfate concentrations. EMM was found to give secondary sulfate concentrations around ten times those with CBM. MARS was used to demonstrate secondary sulfate speciation from the conversions given by CBM. From the CBM calculations, nitrate speciation calculated by MARS was also obtained.