OBSERVATION OF STRATOSPHERIC OZONE DEPLETION IN ROCKET EXHAUST PLUMES

Although modelling studies have predicted(1-7) that particulate and re active gas-phase species in the exhaust plume of large rockets might c ause significant local ozone depletion, the actual response of the str atosphere after rocket launches has never been directly determined. He re we report comprehensive measurements that follow the evolution of s tratospheric ozone in the wake of two Titan IV rockets launched on 12 May and 20 December 1996. In both cases, ozone concentrations dropped to near-zero values in the plume wake, across regions four to eight ki lometres wide, within 30 minutes after launch; intense ozone lass pers isted for 30 minutes after which time concentrations recovered to ambi ent levels. Our data indicate that the number of ozone molecules lost in the plume regions significantly exceed the number of chlorine molec ules deposited by the two rockets, This suggests that a catalytic cycl e based on Cl2O2, other than Cl-2, and unique to solid rocket motor (S PM) plumes might be responsible for our observations. However, the lim ited spatial and temporal extent of the observed ozone losses implies that neither the catalytic Cl2O2 cycle nor other reactions involving e xhaust compounds from large solid-fuelled rockets have a globally sign ificant impact on stratospheric chemistry.