MESOSPHERIC HOX CHEMISTRY FROM DIURNAL MICROWAVE OBSERVATIONS OF HO2,O-3, AND H2O

Microwave (lambda similar to 1.2 mm) spectral emission line observatio ns of HO2, O-3, and (H2O)-O-18 from the upper stratosphere and mesosph ere (45-80 km) were obtained in April 1992, January 1993, and April an d December 1996, using the Kitt Peak National Radio Astronomy Observat ory (NRAO). Significant improvements to this, the only method for maki ng mesospheric HO2 measurements, have been made with hardware upgrades allowing observation of a stronger emission line than described in pr evious work. Data analysis has been improved by (1) recalibration of t he (primarily astronomical) instrument for atmospheric studies, (2) in corporation of updated laboratory spectroscopic work, and (3) use of a n improved photochemical model. Diurnal HO2 data analyses employing 30 min to 2 hour observations show measured HO2 abundances at 50-80 km a ltitude are 23-47% higher than photochemical model values at mid day, agree with model values prior to 0900 local time (LT), and exceed mode l mixing ratios by 70-100% immediately after sunset. Coordinated diurn al measurements of mesospheric O-3 find a model O-3 deficit consistent with model underprediction of ozone seen in all comparable data sets. HOa observations are critical to understanding mesospheric chemistry, in that simultaneous model underpredictions of this ozone-destroying species and of ozone place stringent constraints on proposed sources o f model error. The ozone model deficit and 0900-1800 HO2 model deficit are simultaneously resolved with a 40% reduction in the rate coeffici ent k(HO2 + O --> OH + O-2) We review other modeling studies of this r ate change, indicating it has negligible effect in the lower stratosph ere and improves a diverse set of model results from the upper stratos phere to mesopause.