Simultaneous measurements of stratospheric HO x , NO x , and Cl x : Comparison with a photochemical model

We report simultaneous measurements of the stratospheric concentration profiles of OH, HO 2 , H 2 O 2 , H 2 O, O 3 , HNO 3 , NO 2 , N 2 O, HCl, HOCl, and ClO during a midlatitude balloon flight in 1989. Measurements were made over almost an entire diurnal cycle by the Smithsonian Astrophysical Observatory Far‐Infrared Spectrometer (FIRS‐2) and the Jet Propulsion Laboratory Balloon Microwave Limb Sounder (BMLS). We analyze these measurements using a photochemical model constrained by observations of long‐lived gases. Measured HO x species (OH and HO 2 ) and H 2 O 2 show fair agreement with theory throughout the diurnal cycle. Measurements of HNO 3 are higher than theory near the concentration peak, while the levels of NO 2 are consistent with the model at most altitudes. Measurements of ClO and HOCl are less than predicted concentrations, suggesting a source of HCl in addition to the reaction of Cl with CH 4 . Possibilities for such a source include a minor HCl + O 2 product channel for the reaction of ClO with OH and a minor HCl + O 3 channel for the reaction of ClO with HO 2 .