DISTRIBUTION OF HALON-1211 IN THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE AND THE 1994 TOTAL BROMINE BUDGET

We report here on the details of the first, in situ, real-time measure ments of H-1211 (CBrClF2) and sulfur hexafluoride (SF6) mixing ratios in the stratosphere up to 20 km. Stratospheric air was analyzed for th ese gases and others with a new gas chromatograph, flown aboard a Nati onal Aeronautics and Space Administration ER-2 aircraft as part of the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assess ing the Effects of Stratospheric Aircraft mission conducted in 1994. T he mixing ratio of SF6, with its nearly linear increase in the troposp here, was used to estimate the mean age of stratospheric air parcels a long the EK-2 flight path. Measurements of H-1211 and mean age estimat es were then combined with simultaneous measurements of CFC-11 (CCl3F) , measurements of brominated compounds in stratospheric whole air samp les, and records of tropospheric organic bromine mixing ratios to calc ulate the dry mixing ratio of total bromine in the lower stratosphere and its partitioning between organic and inorganic forms. We estimate that the organic bromine-containing species were almost completely pho tolyzed to inorganic species in the oldest air parcels sampled. Our re sults for inorganic bromine are consistent with those obtained from a photochemical, steady state model for stratospheric air parcels with C FC-11 mixing ratios greater than 150 ppt. For stratospheric air parcel s with CFC-11 mixing ratios less than 50 ppt (mean age greater than or equal to 5 years) we calculate inorganic bromine mixing ratios that a re approximately 20% less than the photochemical, steady state model. There is a 20% reduction in calculated ozone loss resulting from bromi ne chemistry in old air relative to some previous estimates as a resul t of the lower bromine levels.