AIRBORNE IN-SITU OH AND HO2 OBSERVATIONS IN THE CLOUD-FREE TROPOSPHERE AND LOWER STRATOSPHERE DURING SUCCESS

The hydroxyl (OH) and hydroperoxyl (HO2) radicals were measured for th e first time throughout the troposphere and in the lower stratosphere with a new instrument aboard the NASA DC-8 aircraft during the 1996 SU CCESS mission. Typically midday OH was 0.1-0.5 pptv, and HO2 was 3-15 pptv. Comparisons with a steady-state model yield the following conclu sions. First, even in the lower stratosphere OH was sensitive to the a lbedo of low clouds and distant high clouds. Second, although sometime s in agreement with models, observed OH and HO2 were more than 4 times larger at other times. Evidence suggests that for the California uppe r troposphere on 10 May this discrepancy was due to unmeasured HOX sou rces from Asia. Third, observed HO2/OH had the expected inverse depend ence with NO, but was inexplicably higher than modeled HO2/OH by an av erage of 30%. Finally, small-scale, midday OH and HO2 features were st rongly linked to NO variations.