IN-SITU MEASUREMENT OF CL-2 AND O-3 IN A STRATOSPHERIC SOLID ROCKET MOTOR EXHAUST PLUME

The concentration of Cl-2 in the stratospheric exhaust plume of a Tita n IV launch vehicle was measured with a neutral mass spectrometer carr ied on a WB-57F aircraft at 18.9 lan altitude. Twenty nine minutes aft er a twilight Titan IV launch, the mean Cl-2 concentration across an 8 lan wide plume was 126 +/- 44 ppbv, consistent with model predictions that a large fraction of the HCl in solid rocket motor exhaust is con verted into Cl-2 by afterburning reactions in the hot plume. Co-incide nt measurements with ultraviolet absorption photometers also carried o n the aircraft show that ozone concentration in the plume was not diff erent from ambient levels. This is consistent with model predictions t hat nighttime SRM launches will not cause transient ozone loss in the lower stratosphere. The measured Cl-2 concentration equals 15% of the ambient ozone concentration suggesting that transient ozone reduction in SRM plume wakes can be expected after daytime launches when solar u ltraviolet radiation will photolyze the exhaust plume Cl-2.