High-accuracy quantum chemical calculations were performed for several atmospherically important nitrogen oxide derivatives, such as HOONO, HOONO2, NH2NO2, FNO, FNO2, FONO, FONO2, ClNO, ClONO, ClONO2, and ClOONO. The stable conformers of the molecules were identified, and the corresponding heats of formation (Delta H-f(0)o and Delta H-f(298)o) and entropy values (S-298(o)) were computed. On the basis of the thermodynamic functions, equilibrium constants were also calculated for a couple of reactions with importance in the chemistry of the atmosphere. In a number of cases this study provides more reliable estimates for the investigated thermodynamic properties than those can be collected from previous reports.