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 Titan IV launch vehicle was measured with a neutral mass spectrometer carried on a WB-57F aircraft at 18.9 lan altitude. Twenty nine minutes after 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 converted into Cl-2 by afterburning reactions in the hot plume. Co-incident measurements with ultraviolet absorption photometers also carried on the aircraft show that ozone concentration in the plume was not different from ambient levels. This is consistent with model predictions that 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 ultraviolet radiation will photolyze the exhaust plume Cl-2.