EFFECTS ON STRATOSPHERIC OZONE FROM HIGH-SPEED CIVIL TRANSPORT - SENSITIVITY TO STRATOSPHERIC AEROSOL LOADING

The potential impact of high-speed civil transport (HSCT) aircraft emi ssions on stratospheric ozone and the sensitivity of these results to changes in aerosol loading are examined with a two-dimensional model. With aerosols fixed at background levels, calculated ozone changes due to HSCT aircraft emissions range from negligible up to 4-6% depletion s in column ozone at northern high latitudes. The magnitude of the ozo ne change depends mainly on the NO(x) increase due to aircraft emissio ns, which depends on fleet size, cruise altitude, and engine design. T he partitioning of the odd nitrogen species in the lower stratosphere among NO, NO2, N2O5, and HNO3 is strongly dependent on the concentrati on of sulfuric acid aerosol particles, and thus the sensitivity Of O3 to NO(x) emissions changes when the stratospheric aerosol loading chan ges. Aerosol concentrations 4 times greater than background levels hav e not been unusual in the last 2 decades. Our model results show that a factor of 4 increase in aerosol loading would significantly reduce t he calculated ozone depletion due to HSCT emissions. Because of the na tural variability of stratospheric aerosols, the possible impact of HS CT emissions on ozone must be viewed as a range of possible results.