Lower stratospheric chlorine partitioning during the decay of the Mt Pinatubo aerosol cloud

We present measurements of lower stratospheric HCl between July 1992 and August 1996 made by instruments onboard the Upper Atmosphere Research Satellite (UARS). We find that at 46 hPa the fraction of total inorganic chlorine (Cl-y) in the form of HCl increased from 0.68 averaged between July 1992 and June 1993 to 0.78 averaged between July 1995 and June 1996. This increase of (16+/-9)% over three years is much smaller than the trend calculated from in situ measurements made by instruments onboard NASA's ER-2 high-altitude aircraft that has been used to suggest problems with our understanding of lower stratospheric chlorine partitioning. The trend determined from the UARS data is slightly larger than the trend predicted by a two-dimensional model simulation of the atmospheric effects of the Mt. Pinatubo eruption.