The Raman spectroscopy technique has been employed to probe, as a function of temperature, the ionic and molecular speciation within the aqueous phase for systems of potential relevance to stratospheric chemistry. The systems studied, over the temperature range 200-300 K, were (i) binary HNO3:H2O and H2SO4:H2O mixtures and (ii) ternary HNO3:H2SO4:H2O (NSW) mixtures. The contributions of the concentration coefficient, Q(m), to the equilibrium dissociation constants were assessed from the spectroscopic data. It was observed that speciation within the binary acid systems shifts toward the ionized form as temperature and concentration decrease because of increasing proton stabilization. The ternary NSW acid displays some similar properties to the binary counterparts, though a dominance of SO4aq2- over NO3aq- ions in the competition for protons is observed. This effect leads to the HSO4- ion becoming the principal associated acid form and its presence is found to determine the behavior of the NSW systems at all studied concentrations. The frozen acids are observed to be totally ionized, and detailed thermodynamic measurements of the freezing solutions suggest that homogeneous freezing will not occur at temperatures and concentrations for which associated species proliferate. It was found that the onset of freezing could be monitored spectrally by observation of an increasing scatter intensity maximizing at 300 cm(-1). Observation of this phenomenon therefore provided an indirect method of determining the temperature at which the solid-phase began to grow.