In situ measurements of HO_x in aircraft exhaust plumes and contrails during SUCCESS

In situ flight measurements of the hydroxyl (OH) and hydroperoxyl (HO₂) radicals were performed in the exhaust plume of a Boeing 757 and in the contrail of a Douglas DC-8 flying under typical cruise conditions in the upper troposphere and lower stratosphere during the SUCCESS mission of April and May 1996. Measurements were made in a range of exhaust plume ages from roughly 10 seconds to 20 minutes. OH mixing ratios were found to be greatly enhanced in the plumes, to 2-5 pptv from a background of 0.3-0.5 pptv in young plumes, and to 0.6 pptv from a background of ≤0.2pptv in older contrails. HO₂ mixing ratios were heavily suppressed in the plumes, to 2-4 pptv from a background of 10-20 pptv, for both young plumes and older contrails.