The equilibrium partial vapor pressures over the binary solutions H2O/HNO3, H2SO4/H2O, HNO3/H2SO4 and the ternary mixture H2SO4/HNO3/H2O have been re-determined for temperatures below 25 ¿C. The model presented here is valid over the entire range of concentrations, for temperatures in the range 190--298 K. The predictions of this model are compared with the existing measurements and other predictions, both at room temperature and at low temperatures down to about 190 K. The calculated partial pressures agree very well with the available experimental data. ¿ American Geophysical Union 1996