To understand the chemodynamic role of vegetation in a multimedia system, the rate and extent of chemical partitioning from adjacent environmental media and the rate of chemical transformation associated with vegetation need to be determined. An exposure system was used to isolate and expose above ground vegetation to semi-volatile air contaminants. Measurements of phenanthrene, anthracene, fluoranthene and pyrene in the chamber air and the plant tissue were collected during both the uptake and clearance phase of exposure events. The measurements were fitted to the mass balance of the system by simultaneously optimizing estimates of the plant/air partition coefficient, the interfacial mass transfer coefficient and first-order reaction rates in the air and plant. In addition to providing information about the partitioning and mass transfer characteristics of the system, the measurements indicate that a degradation pathway may exist at or near the plant/air interface. Implications of this loss pathway are presented in the context of a multimedia model.