In-situ measurement of Cl sub(2) and O sub(3) in a stratospheric solid rocket motor exhaust plume

The concentration of Cl sub(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 km altitude. Twenty nine minutes after a twilight Titan IV launch, the mean Cl sub(2) concentration across an 8 km wide plume was 126 plus or minus 44 ppbv, consistent with model predictions that a large fraction of the HCl in solid rocket motor exhaust is converted into Cl sub(2) by after-burning reactions in the hot plume. Coincident 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 sub(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 sub(2).