Correlated observations of HCl and ClONO₂ from UARS and implications for stratospheric chlorine partitioning

We present the first near‐global set of correlated measurements of stratospheric HCl and ClONO 2 concentrations. These data, obtained from the Upper Atmosphere Research Satellite (UARS) between August 1992 and March 1993, are analyzed using the Goddard trajectory mapping technique. These data indicate that, between 20 and 30 km altitude and 60°N to 60°S latitude, total inorganic chlorine (Cl y ) is fairly evenly distributed between ClONO 2 and HCl, with HCl the slightly more dominant reservoir. The sum of UARS measurements of HCl and nighttime ClONO 2 , which approximates Cl y at these altitudes, closely agrees with Cl y derived from a tracer‐Cl y relation originally derived from aircraft data, increasing confidence in the UARS data. Comparisons between these data and two‐dimensional model results suggest that models underpredict ClONO 2 (overpredict HCl) near 20 km and overpredict ClONO 2 (underpredict HCl) near 30 km, although the 20‐km underprediction is not as large as analyses of aircraft measurements have indicated.