STUDY OF HETEROGENOUS REACTIONS OF POLYCYCLIC AROMATIC-HYDROCARBONS .1. WEAKENING OF PAH-SUPPORT BONDS UNDER PHOTONIC IRRADIATION

The various parameters determining the reactions of PAH in the particulate phase are studied. An alternating pulsed-flow reactor allowing continuous mixing of the particles and evacuation of the reactant gases, has been constructed. A preliminary study of the photolysis of particulate PAH by sunlight and in the absence of oxidizing gases shows that photolysis is negligible for short irradiation times (< 2 h) for most of the 6 PAH studied: anthracene, fluoranthene, pyrene, benzo[a]pyrene, benzo[ghi]perylene and benzo[b]fluoranthene, and for the two substrates used: alumina and fly ash. On the other hand, this study shows that the particle surface is deactivated and that the PAH-support bonds are weakened; there is partial desorption of PAHs under photonic impact. Two types of PAH are present in the particulate phase: reversibly physisorbed and irreversibly chemisorbed PAH. This phenomenon has not been considered in kinetic studies. It may even cast some doubt upon the determination of atmospheric concentrations which are probably underestimated by classical analytical methods.