Vegetation fires are a major source of atmospheric trace gases and particles. Gas-phase photochemistry, production of secondary aerosol compounds, and coagulation of particles can substantially change the chemical and radiative properties of the initial fire emissions during the first few hours after emission. Better modeling of these initial transformations should help improve estimates of the chemical and radiative impact of vegetation fires. We present a combined gas-phase chemistry and aerosol dynamics model designed to investigate the transformation of particles within young combustion plumes. The model simulates the plume evolution in a diluting Lagrangian parcel. The gas-phase chemical mechanism predicts the secondary formation of ozone, sulfate, nitrate, and semi-volatile organic compounds (SVOCs) within the young plume. The aerosol dynamics module predicts the transfer of chloride, nitrate, ammonium, and SVOCs between the gas and particle phases, the change in the particle size distribution due to mass transfer between phases and coagulation, and the change in the optical properties of the particles. The model results are compared to field measurements of savannah fires obtained during the SAFARI 2000 campaign. Preliminary results suggest that the model under predicts the secondary formation of ozone, sulfate, and condensed organic matter (COM) relative to observations. The rapid formation of ozone within the plume is driven by the oxidation of aldehydes, ketones, olefins, phenols and furans; other hydrocarbons are found to have a negligible impact on predicted ozone production. Furans appear to play an important role in the formation of both ozone and SVOCs within the plume due to their high initial concentration, rapid reaction rate and high molecular weight. Possible explanations for the discrepancy between model results and field observations are explored, including uncertainty in dilution rates, photolysis rate constants, heterogeneous reaction rates, emission factors, and thermodynamic parameters.