Deliquescence of Multicomponent Aerosols

Following Wexler and Seinfeld (1991), let us consider two electrolytes in a solution exposed to the atmosphere. The change of the DRH of a single-solute aqueous solution when another electrolyte is added can be calculated using the Gibbs-Duhem equation, (10.21). For constant T and p and for a solution containing two electrolytes (1 and 2) and water (w)  

1 does not change, because it remains in equilibrium with its solid phase. Thus d il = 0 in (10.73). The chemical potentials of electrolyte 2 and water can be expressed using (10.51) to get 

Accounting for the fact that n2/nw = Mwm2j1000, where m2 is the molality of electrolyte 

Wexler and Seinfeld (1991) have argued that da Jdm2 0 and therefore the integral is positive, and then 

Hence the activity of water decreases as electrolyte 2 is added to the system, until the solution becomes saturated in that electrolyte, too. The aerosol is exposed to the atmosphere and therefore its DRH also decreases. 

There are seven different RH composition regimes in the figure  

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