Binary Nucleation in the H2SO4-H2O System

In a gas containing water vapor, H2SO4 molecules exist in various states of hydration  

H2SO4 H2O, H2SO4 2H2O.H2SO4 h H2O. Nucleation of H2SO4 and H2O is then 

Sulfuric acid-water nucleation falls into the category where component B (H2SO4) is present at a very small concentration relative to that of A (H2O), yet the critical cluster is not dilute with respect to H2SO4. Thus the preexponential factor (10.94) applies. The rate 

TABLE 10.5 Equilibrium Constants Kf, at 298 K for the Successive Addition of a Water Molecule to a Hydrated Sulfuric Acid Molecule 

To calculate the nucleation rate of H2SO4-H2O, first AG(/iai ns,T) has to be evaluated to locate the saddle point. One can construct a table of AG as a function of and rig and the saddle point can be found by inspection of the values. To calculate AG one needs values for activities, densities, and surface tensions as functions of temperature. The value of the saturation vapor pressure of H2SO4 has a major effect on the nucleation rate. Kulmala and Laaksonen (1990) have evaluated available expressions for the H2SO4 saturation vapor pressure and derived a recommended expression (Table 10.6). Table 10.7 illustrates a particular calculation of AG as a function of /ia and (neglecting hydration). 

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