AN ABSORPTION-MODEL OF THE GAS AEROSOL PARTITIONING INVOLVED IN THE FORMATION OF SECONDARY ORGANIC AEROSOL

A partitioning model is developed to allow the modeling of the dynamic s of secondary organic aerosol (SOA) formation. The gas/aerosol partit ioning is assumed to be governed by equilibrium partitioning into an a bsorptive, well-mixed liquid (or at least amorphous) organic matter (o m) phase. The model is represented using a set of coupled linear equat ions. It may be especially applicable when photochemical smog is being formed in the summer. The model permits (indeed, it requires) partiti oning of a given compound i to occur even when i is present at a level below its saturation vapor pressure. During early periods of SOA form ation, to determine the partitioning for each compound of interest, th e model must be solved iteratively for each time and location of inter est, Iteration is required because the partitioning is assumed to be g overned by mole fraction concentrations in the om phase, and because p rior to solving the problem, one does not know the total number of mol s of condensed compounds in the om phase. During later stages of SOA f ormation, if the amount and general composition of the SOA begin to be come constant, the partitioning coefficient of each of the compounds w ill also stabilize, and an iterative solution will be less needed.