Mathematical model for gas-particle partitioning of secondary organic aerosols

A dynamic model is developed for gas-particle absorptive partitioning of semi-volatile organic aerosols. The model is applied to simulate a pair of m-xylene/NOx outdoor smog chamber experiments. In the presence of an inorganic seed aerosol a threshold for aerosol formation is predicted. An examination of characteristic times suggests conditions where an assumption of instantaneous gas-particle equilibrium is justified. Semi-volatile products that are second-generation, rather than first-generation, products of a parent hydrocarbon cause a delay in aerosol formation due to the delayed rate at which the second-generation products are formed. The gas-particle accommodation coefficient is the principal transport parameter and is estimated to have a value between 1.0 and 0.1 for the m-xylene aerosol.