For reactions of the HSCH2 radical with atmospheric gases O-2, NO, and NO2, we describe the thermochemistry by HF, MP2, and density functional computational methods, by Petersson's complete basis set extrapolation (CBS-4 and CBS-Q), and, in part, by Pople's G2MP2 model chemistry method. We offer recommendations of values of heats of formation for the participants in these reactions, which differ in some cases from the estimates based on the group additivity principle. The least expensive post-Hartree-Fock methods provide a coherent account of the thermochemistry, but are not superior to group additivity estimation.