Abstract. We report here on the details of the first, in situ, real-time measurements of H-1211 (CBrC1F2) and sulfur hexafluoride (SF6) mixing ratios in the stratosphere up to 20 km. Stratospheric air was analyzed for these gases and others with a new gas chromatograph, flown aboard a National Aeronautics and Space Administration ER-2 aircraft as part of the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission conducted in 1994. The mixing ratio of $F6, with its nearly linear increase in the troposphere, was used to estimate the mean age of stratospheric air parcels along the ER-2 flight path. Measurements of H-1211 and mean age estimates were then combined with simultaneous measurements of CFC-11 (CC13F), measurements of brominated compounds in stratospheric whole air samples, and records of tropospheric organic bromine mixing ratios to calculate 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 photolyzed to inorganic species in the oldest air parcels sampled. Our results for inorganic bromine are consistent with those obtained from a photochemical, steady state model for stratospheric air parcels with CFC-11 mixing ratios greater than 150 ppt. For stratospheric air parcels with CFC-11 mixing ratios less than 50 ppt (mean age >5 years) we calculate inorganic bromine mixing ratios that are approximately 20% less than the photochemical, steady state model. There is a 20% reduction in calculated ozone loss resulting from bromine chemistry in old air relative to some previous estimates as a result of the lower bromine

A new instrument, the Airborne Chromatograph for Atmospheric Trace Species IV (ACATS‐IV), for measuring long‐lived species in the upper troposphere and lower stratosphere is described. Using an advanced approach to gas chromatography and electron capture detection, the instrument can detect low levels of CFC‐11 (CCl3F), CFC‐12 (CCl2F2), CFC‐113 (CCl2F‐CClF2), methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), nitrous oxide (N2O), sulfur hexafluoride (SF6), Halon‐1211 (CBrClF2), hydrogen (H2), and methane (CH4) acquired in ambient samples every 180 or 360 s. The instrument operates fully‐automated onboard the NASA ER‐2 high‐altitude aircraft on flights lasting up to 8 hours or more in duration. Recent measurements include 24 successful flights covering a broad latitude range (70°S–61°N) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign in 1994.

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An in situ gas chromatograph (GC) instrument on a balloonborne package is described in detail and data from seven science deployments are presented. This instrument, the Lightweight Airborne Chromatograph Experiment (LACE), operates on the Observations of the Middle Stratosphere (OMS) in situ gondola and has taken data from the upper troposphere to near 32 km with a vertical resolution of better than 300 m. LACE chromatography has been developed to measure halon‐1211, the chlorofluorocarbons (CFC‐11, CFC‐113, CFC‐12), nitrous oxide (N2O), and sulfur hexafluoride (SF6) every 70 s and methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), hydrogen (H2), methane (CH4), and carbon monoxide (CO) every 140 s. In the introduction we present scientific motivation for choosing this suite of molecules and for the use of faster sample rates resulting in unprecedented vertical resolution from an in situ GC. Results from an intercomparison with the Airborne Chromatograph for Atmospheric Trace Species (ACATS‐IV) instrument are shown to quantitatively connect this LACE data set to the complementary data set generated on board the NASA ER‐2 aircraft.

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