The stratospheric aerosol and its impact on stratospheric chemistry

Abstract

A review with many refs. A persistent mist of fine particles is found in the lower stratosphere. Away from the winter pole, these particles consist primarily of sulfuric acid and water. Explosive volcanic eruptions often provide the sulfur. Between eruptions, anthropogenic and natural sources of long-lived sulfur species appear sufficient to maintain the sulfate layer, but they have not been quantified. Near the winter pole, polar stratospheric clouds form from nitric acid and water. The details of the compn. and phase of the nitric acid-water clouds remain to be discovered, but they are known to form at temps. above the frost point. Below the frost point, clouds are predominately water ice. The size, compn. and dynamics of the aerosol and cloud particles help det. their lifetimes and chem. impact. The stratospheric aerosol has a very significant impact on the chem. of the stratosphere. In the polar winter, reactions on cloud particles free the chlorine in hydrochloric acid and chlorine nitrate. When the polar air is exposed to sunlight, this chlorine participates in rapid, catalytic destruction of ozone. In mid-latitudes, the hydrolysis of N2O5 on the surface of sulfate particles leads to the redn. of NOx and the increase of ozone-destroying chlorine and hydrogen radicals. The performance of models describing the chem. of the lower stratosphere is dramatically improved when reactions on surfaces of aerosol and cloud particles are included. The new models have been tested against coordinated measurements of many of the key species made simultaneously from aircraft.