Keith Bein - Activity interpretation in H2O-H2SO4 binary nucleation

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  Publication Details (including relevant citation   information):

  Bein, K.J., and A.S. Wexler (2007), Activity interpretation in   H2O-H2SO4 binary nucleation,   Journal

         of Chemical Physics, 127, 124316.


       Sulfuric acid-water nucleation is   thought to be a key atmospheric mechanism for forming new   condensation nuclei.  In earlier literature, measurements of   sulfuric acid activity were interpreted as the total (monomer   plus hydrate) concentration above solution.  Due to recent   reinterpretations, most literature values for   H2SO4 activity are thought to represent the   number density of monomers.  Based on this reinterpretation,   the current work uses the most recent models of   H2O-H2SO4 binary nucleation   along with perturbation analyses to predict a decrease in   critical cluster mole fraction, increase in critical cluster   diameter, and orders of magnitude decrease in nucleation   rate.  Nucleation rate parameterizations available in the   literature, however, give opposite trends.  To resolve these   discrepancies, nucleation rates were calculated for both   interpretations of H2SO4 activity and   directly compared to the available parameterizations as well as   the perturbation analysis.  Results were in excellent   agreement with older parameterizations that assumed   H2SO4 activity represents the total   concentration and duplicated the predicted trends from the   perturbation analysis, but differed by orders of magnitude from   more recent parameterizations that assume   H2SO4 activity represents only the   monomer.  Comparison with experimental measurements   available in the literature revealed that the calculations of the   current work assuming aa  represents the total concentration are most frequently in   agreement with observations.

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