Pitzer activity coefficient models are developed, using a wide range of data at 298.15 K, for the following systems containing succinic acid (H(2)Succ) and/or succinate salts: {H+, Li+, Na+, K+, Rb+, Cs+}Cl--H-2-Succ- H2O, HNO3-H(2)Succ-H2O, H+-NH4+-HSucc(-)-Succ(2-)-NH3-H(2)Succ-H2O, NH4Cl-(NH4)(2)Succ-H2O, H+-Na+-HSucc(-)-Succ(2-)-Cl--H(2)Succ-H2O, NH4NO3-H(2)Succ-H2O, and H2SO4-H(2)Succ-H2O. The above compositions are given in terms of ions in the cases where acid dissociation was considered. Pitzer models were also developed for the following systems containing malonic acid (H(2)Malo): H+-Na+-HMalo(-)- Malo(2-)-Cl--H(2)Malo-H2O, and H(2)Malo-H2SO4-H2O. The models are used to evaluate the extended Zdanovskii-Stokes-Robinson (ZSR) model proposed by Clegg and Seinfeld (J. Phys. Chem. A 2004, 108, 1008-1017) for calculating water and solute activities in solutions in which dissociation equilibria occur. The ZSR model yields satisfactory results only for systems that contain moderate to high concentrations of (nondissociating) supporting electrolyte. A practical modeling scheme is proposed for aqueous atmospheric aerosols containing both electrolytes and dissociating (organic) nonelectrolytes.