Dissolution and Gas-Particle Partitioning of Organic Compounds

The thermodynamic principles introduced in Chapter 10 can be used to investigate the partitioning of organic compounds between the gas and aerosol phases. We will first focus on the analysis of a series of idealized scenarios and then discuss their applicability to the atmosphere. 

Noninteracting Secondary Organic Aerosol Compounds The simplest case is that of a compound that does not interact with already existing aerosol components. Such a compound does not adsorb on the aerosol surface or form solutions with the existing aerosol and gas-phase species. Let us assume that a reactive organic gas (ROG) undergoes atmospheric oxidation to produce products, P1 P2, and so on 

and caerji, are the total, gas-phase, and aerosol-phase concentrations in pgm-3 of product i, then 

With noninteracting aerosol components, P, exists in the aerosol phase as pure P,. Thus gas-aerosol equilibrium is reached for P, when the gas-phase concentration, cg l. is that corresponding to the vapor pressure of pure i at that temperature, ceq i = p°Mj/RT, where Mi is its molecular weight. Thus at equilibrium 

If Ctj Ceq.i the equilibrium condition of (14.8) cannot be satisfied because it would require negative aerosol concentrations. Therefore the aerosol concentration of species i will be 

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