veloped for laboratory studies of the degradation of absorbed PAH under simulated environmental conditions.The reactor is inexpensive, is simple to construct and operate, and is three dimensional, i.e., particles can be suspended in air or other gases during irradiation. In contrast to a flow-through system, the fluidized-bed photoreactor permits unlimited reaction time. It is possible to vary the photoreactor system over a wide range of conditions. Specifically, the adsorbed compound, gas composition, particle substrate, light intensity, humidity, and temperature may be varied, and a wide range of particles sizes can be used in the reactor. The reactor is suitable for studies of both the rates and products of degradation of PAH since relatively large samples are available for analyses. Most importantly, the rates of degradation determined in the photoreactor have been shown to be highly reproducible, generally to within ±20% or less at the 95% confidence level.