In this paper we have attempted to quantify the loss of polyaromatic hydrocarbons (PAH) on atmospheric soot particles with respect to the effects of humidity, solar radiation, and temperature. Dilute residential wood smoke and internal gasoline combustion emissions were individually aged in the presence of natural sunlight in 25-m/sup 3/ outdoor Teflon film chambers. Soot particles were collected on filters and analyzed for PAH. In each experiment first-order rate constants were computed for the disappearance of individual PAH. Rate expressions as a function of humidity, light, and temperature were then generated for nine different PAH from the wood smoke experiments. Estimates suggest that, at moderate humidities and temperatures. PAH half-lives in the chamber atmosphere were of the order of 1 h. At very low angle sunlight, very low water vapor concentrations, or very low temperatures. PAH daytime half-lives on airborne soot particles increased for many compounds to a period of days.