DEVELOPMENT AND APPLICATION OF A DUAL-IMPEDANCE RADIAL DIFFUSION-MODEL TO SIMULATE THE PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS IN COMBUSTION AEROSOLS

The fate of semivolatile organic compounds in the atmosphere is largel y dependent on their partitioning between the gas phase and sorption t o particulate matter. Since real atmospheres have been shown to deviat e significantly from gas-particle equilibrium under certain conditions , dynamic mass transfer models are needed to accurately predict partit ioning. In this work, a dual-impedance radial diffusion model is prese nted that is able to simulate the partitioning of deuterated fluoranth ene in wood and diesel soot atmospheres generated in a large outdoor T eflon film chamber. It is shown that the dual-impedance model produces significantly better fits to experimental results than a one-layer mo del and that surface mass transfer is not rate limiting in these syste ms. The sensitivity of optimized apparent diffusion coefficients to ke y input parameters is also explored. This work lays the foundation for incorporating dynamic gas-particle partitioning models into larger at mospheric models, such as urban airshed models. By conducting experime nts under various conditions (e.g., temperature and humidity), values for apparent diffusivities as a function of compound, particle source, and atmospheric conditions may be developed. After including photoche mical reactions, the model may be used to predict the fate of semivola tile organic compounds in real atmospheres.