Molecular Beam Studies of Reactions Between Stratospheric Gases and Supercooled Sulfuric Acid

摘要

Sulfuric acid aerosols in the stratosphere contribute to the destruction of the ozone layer by converting inactive gases like HCl and HBr into molecules that fall apart into chlorine and bromine atoms, which catalytically destroy ozone. The first step in these reactions is the transport of gaseous HCl and HBr into the acid droplet, where they dissolve and dissociate. We find that the entry of HCl and HBr into sulfuric acid is often frustrated by immediate HCl and HBr evaporation from the surface of the acid. For mid-latitude, 70 wt % sulfuric acid, only 11% of the HCl and 22% of the HBr molecules that strike the acid surface enter into the bulk. These entry probabilities rise to 70% for HCl and 90% for HBr in 54 wt % sulfuric acid, typical of higher latitudes. We also find that HCl is 20 times more soluble than predicted in 70 wt % sulfuric acid. This high solubility implies that, although few HCl molecules enter mid-latitude aerosols, those that do enter the acid dissolve for longer than expected, making them more likely to react with other solute species.