SPACE SHUTTLES IMPACT ON THE STRATOSPHERE - AN UPDATE

To assess their impact on the stratosphere, a launch scenario of nine shuttles and three Titans per year is simulated in a two-dimensional p hotochemistry and transport model that includes heterogeneous reaction s on a stratospheric sulfate aerosol (SSA) layer and polar stratospher ic clouds (PSCs). These rocket launches are predicted to cause small c onstituent changes in the stratosphere. Maximum total inorganic chlori ne enhancements are computed to be about 12 parts per trillion by volu me (similar to 0.4% on a 3 parts per billion by volume background) in the middle to upper stratosphere at northern middle to high latitudes. Maximum ozone decreases associated with these chlorine increases are calculated to be about 0.14% in the middle to upper stratosphere at no rthern middle to high latitudes. Column ozone decreases are predicted to be a maximum of about 0.05% at northern polar latitudes in the earl y spring. Model results using (1) gas phase only reactions, (2) gas ph ase reactions and heterogeneous reactions on the SSA layer, and (3) ga s phase reactions and heterogeneous reactions on the SSA layer and PSC s have also been compared with one another. The simulations from these three versions of our model gave annually averaged global total ozone decreases of (1) 0.0056%, (2) 0.010%, and (3) 0.014%. Stratospheric e ffects from heterogeneous reactions promoted by the alumina emitted fr om these rockets could be larger than those predicted from the chlorin e emissions and need to be investigated further.