Sulfuric acid — water system, vapour

It is convenient to use phase diagrams [46] to represent the thermodynamic properties that determine the stability and equilibrium composition of water-containing aerosols. The properties of interest are the temperature, the vapour pressure and composition of the various components in the condensed phases. This is particularly important with respect to the composition and stability of the various hydrates formed at low temperature in the nitric acid-water [47] and sulfuric acid-water binary systems [48], and the ternary systems HjSO/HNOj/HjO and HjSO/HCl/HjO [49],... 

Vapour pressures for a number of atmospherically relevant condensed systems have been measured with mass spectrometry. These systems include hydrates of HC1, HjS04 and HNO, supercooled liquids and pure water-ice, as well as the interactions of HC1 vapour with die solids, ice and NAT [23,47,50-55]. Vapour pressure measurements over HNOj/HjO hydrates have also been made using infrared optical absorption with light originating from a tunable diode laser [29]. This technique allowed the identification of the metastable NAD in presence of the more stable NAT under temperature and vapour pressure conditions near to those found in the polar stratosphere. Vapour pressures of Up, HN03, HC1, HBr over supercooled aqueous mixtures with sulfuric acid have been calculated using an activity model [56]. It provides a parameterized model for vapour pressures over the stratospheric relevant temperatures (185-235 K). 

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