LABORATORY MEASUREMENTS OF HETEROGENEOUS REACTIONS ON SULFURIC-ACID SURFACES

Increasing evidence from field, modeling, and laboratory studies sugge sts that heterogeneous reactions on stratospheric sulfate aerosol part icles may contribute to global ozone depletion. Using a Knudsen cell r eactor technique, the authors have studied the uptake, reactivity, and solubility of several trace atmospheric species on cold sulfuric acid surfaces representative of stratospheric aerosol particles. The resul ts suggest that the heterogeneous conversion of N2O5 to HNO3 is fast e nough to significantly affect the partitioning of nitrogen species in the global stratosphere and thus contribute to global ozone depletion. The hydrolysis of ClONO2 is slower and unlikely to be important under normal conditions at midlatitudes. The solubilities of HCl and HNO3 i n sulfuric acid down to 200 K were found to be quite low. For HCl, thi s means that little HCl is available for reaction on the surfaces of s tratospheric sulfate aerosol particles. The low solubility of HNO3 mea ns that this product of heterogeneous reactions will enter the gas pha se, and the denitrification observed in polar regions is unlikely to o ccur in the global stratosphere.