Hydrates in binary sulfuric acid-water vapor: Comparison of CIMS measurements with the liquid-drop model

We report calculations of the distribution of sulfuric acid-water hydrates under atmospheric conditions using the liquid-drop hydrate model. The model-computed total acid concentrations (free acid plus hydrated acid) are compared with chemical ionization mass spectrometer (CIMS) measurements of total sulfuric acid vapor over solutions of varying concentration [Marti et al., 1997] Results from this first direct comparison with experimental measurement suggest that the liquid-drop model overestimates the extent of hydrate formation. We explore the consequences of this overestimation on binary sulfuric acid-water nucleation rates, and on higher-order multicomponent nucleation rates involving these and additional trace species in the atmosphere. In particular, it is found that overestimation of hydrate formation by the model can result in substantial underprediction of sulfuric acid-water nucleation rates.