STUDY OF HI, HBR AND NO2 ADSORPTION ON GRAPHITE AND SILVER AEROSOL-PARTICLES USING SHORT-LIVED ISOTOPES

Radiochemical techniques were used to study in situ the adsorption of halides and nitrogen dioxide on aerosol particles. Using short-lived i sotopes, (HI)-I-136, (HBr)-Br-86, and (NO2)-N-13 molecules were synthe sized and adsorbed on graphite and silver aerosols. By measuring tempe rature-dependent desorption of these compounds from the particles, ads orption enthalpies could be determined for adsorption on silver partic les, which agree well with data on macroscopic surfaces. The unexpecte d shapes of the desorption curves from graphite particles are probably due to a distribution of different adsorption sites. The preparation of the aerosol for the desorption study gave also interesting insights into the adsorption process. In spite of rather high adsorption entha lpies the sticking probability of (HI)-I-136 On silver particles seeme d to be rather low. It was concluded that the molecules accommodating on the surface in a physisorbed state may either chemisorb or desorb b ack into the gas. This model could explain the strong temperature depe ndence of the chemisorption rate.