Combustion aerosols are an important source of toxic atmospheric compounds, a major class of which is polycyclic aromatic hydrocarbons (PAHs). Photodegradation is an important atmospheric loss mechanism for PAHs. Combustion aerosols consist of an elemental carbon core and an organic layer. Several recent studies show that aerosol surface characteristics influence PAH photodegradation rates. Recent research indicates that organic layer constituents also strongly influence PAH photodegradation in organic liquids. These results prompted an investigation of the relative importance of aerosol surface characteristics versus composition of the organic layer. Organic compounds found on combustion aerosols were incorporated on carbon black particles to simulate a heterogeneous aerosol environment. Organic compounds identified in diesel soot, and wood soot combustion aerosols were investigated to determine their influence on PAH reactivity. Solutions containing dissolved PAHs, and the organic compounds were syringe spiked on to a carbon black surface. A liquid dispersion technique for obtaining thin, even coatings of the organic particulate matrix on Teflon filters was used to facilitate UV light exposure to the synthesized particle matrices. The filter supported aerosol matrices were exposed to UV light in a photochemical turntable reactor. The photodegradation rate of polycyclic aromatic hydrocarbons is significantly enhanced when isoeugenol, a compound found on wood combustion aerosols, is present with the PAH in the organic layer on elemental carbon particles. These results indicate that constituents which coexist with PAH in the organic layer around the elemental core influence the reactivity of PAHs on combustion aerosols. Further evaluation of specific chemical and physical properties of the organic layer and the elemental surface using the developed technique will lead to better characterization of PAH reactivity on combustion aerosol surfaces. Organic compounds found on combustion particles are a major source of atmospheric pollutants which adversely affect human health. This investigation of physical and chemical factors influencing reactivity contributes to the knowledge about the stability, transport, and bioavailability of toxic compounds on combustion particles in the atmosphere.