The Effects of Rocket Exhaust on Stratospheric Ozone: Chemistry and Diffusion

This study extends the work of M. R. Denison et al. (Journal of Spacecraft and Rockets, v31 n3, p435-442, May-June 1994) who described a methodology that allowed the quantitative assessment of the impact of rocket exhaust on stratospheric ozone. The local, short time, effect and the ultimate global effect of rocket exhaust are evaluated through the use of a high-resolution ozone imager (HIROIG). Analysis of solid rocket motor (SRM) induced depletion of ozone during a TITAN III launch showed that the level of ozone column density loss was about 0.25% over an area of 20 km after 2 hours. After 9 hours, the plume size increased and the affected area increased to 70 km at approximately 0.1%. In the north pole region, the loss peaks at about 0.06% while the rest of the globe has a loss of about 0.01%. The local hole produced by a single SRM launch is approximately 2 km to 4 km in radius and persists for a few thousand seconds after which it fills in by diffusion. Plume transport takes place in the upper stratosphere on a level much larger than in the lower stratosphere as a result of strong stratospheric winds. The plume tends to remain in the neighborhood of the launch site for as long as 9-10 hours with about 70% recovery from the initial ozone depletion. In winter launches the plume tends to linger near the launch site longer than in summer launches. The long-term global impact of a single 2.4 million pound SRM in steady state is estimated to be a 0.001% to 0.006% reduction of stratospheric ozone per year. Loss of stratospheric ozone caused by liquid rocket engine boosters that produce nitric oxide is considerably less than that caused by SRM boosters, which produce large amounts of chlorine in the boost phase. The nitric oxide catalytic cycle mechanism causes less ozone destruction than chlorine. At present, all large-thrust U.S. launch vehicles are chlorine-based SRMs. This work also provides inputs for further refining the HIROIG. (4 tables, 100 figures, 23 ref7 Prepared in collaboration with the Department of Earth, Atmospheric and Planetary Sciences and the Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, and the Lawrence Livermore National Laboratory, Livermore, CA.