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A consistent set of thermochemical property values, Δ f H °, Δ f G °, S °, and C p o , at 298.15 K is given for the known constituents of aqueous sulfur dioxide ( SO 2 0 ( aq ) , HSO 3 - ( aq ) , SO 3 2 - ( aq ) , H + (aq), and S 2 O 5 2 - ( aq ) ). Also tabulated are values of the mean ionic activity coefficients, osmotic coefficients, partial pressure of SO 2 (g), and the relative apparent molar enthalpy as a function of concentration of SO 2 (aq) at 298.15 K. The data analysis considered a wide variety of measurement techniques: calorimetric enthalpies of solution and reaction, heat capacities, equilibrium constants, solubilities, and vapor pressure measurements, both partial and total, over aqueous solutions of SO 2 for the temperature range 278 to 393 K. All auxiliary data have been taken from the most recent set of CODATA values which were converted to a standard state pressure of one bar (0.1 MPa). For the process SO 2 ( g ) = SO 2 0 ( aq ) , the selected "best" values are: K = 1.23±0.05 mol kg -1 bar -1 , Δ G ° = -0.5±0.10 kJ mol -1 , Δ H ° = -26.97±0.30 kJ mol -1 , and Δ C p o = 155 ± 10 J mol - 1 K - 1 . The standard state partial molar entropy of SO 3 2 - ( aq ) , obtained by the analysis of data via two independent thermodynamic pathways is -15.40±0.80 J mol -1 K -l at 298.15 K. Parameters are given which extend the predictions to temperatures up to 373 K.