Modeling the Mass Transfer of Semivolatile Organics in Combustion Aerosols

Abstract

A radial diffusion model was developed to describe the dynamic mass transfer of semivolatile organics into and out of combustion aerosols. The model combustion aerosol consists of a solid carbon core that is surrounded by a viscous, liquid-like, organic layer. Diffusion takes place only within the organic layer and is controlled by mass transfer at the particle surface. Modeling of semi volatiles requires the tuning of two separate parameters: a diffusion coefficient (D) and a surface mass transfer coefficient (α). Preliminary testing of the model on the uptake of deuterated pyrene by diesel exhaust aerosol at a temperature of 25 °C suggests that diffusion coefficients for PAH are of the order of 10^(-15) cm^2/s and that surface mass transfer coefficients for pyrene are of the order of 10^(-10) cm/s.

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