Chemical Potential of Water in Atmospheric Particles

Water vapor exists in the atmosphere in concentrations on the order of grams per m3 of air while its concentration in the aerosol phase is less than lmgm 3 of air. As a result, transport of water to and from the aerosol phase does not affect the ambient vapor pressure of water in the atmosphere. This is in contrast to the cloud phase, where a significant amount of water exists in the form of cloud droplets (see Chapter 17). Thus the ambient RH can be treated as a known constant in aerosol thermodynamic calculations. Considering the equilibrium 

Water equilibrium between the gas and aerosol phases at the point of deliquescence requires that the deliquescence relative humidity of a salt will then satisfy 

TABLE 10.2 Solubility of Common Aerosol Salts in Water as a Function of Temperature (n = A + BT + CT2, n = mol of solute per mol of water) 

FIGURE 9.5 Gibbs free energy of a solid salt and its aqueous solution as a function of RH. At the DRH these energies become equal. 

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