Volume mixing ratio (VMR) profiles of the chlorine‐bearing gases HCl, ClONO2, CCl3F, CCl2F2, CHClF2, CCl4, and CH3Cl have been measured between 3 and 49° northern‐ and 65 to 72° southern latitudes with the Atmospheric Trace MOlecule Spectroscopy (ATMOS) instrument during the ATmospheric Laboratory for Applications and Science (ATLAS)‐3 shuttle mission of 3 to 12 November 1994. A subset of these profiles obtained between 20 and 49°N at sunset, combined with ClO profiles measured by the Millimeter‐wave Atmospheric Sounder (MAS) also from aboard ATLAS‐3, measurements by balloon for HOCl, CH3CCl3 and C2Cl3F3, and model calculations for COClF indicates that the mean burden of chlorine, ClTOT, was equal to (3.53±0.10) ppbv (parts per billion by volume), 1‐sigma, throughout the stratosphere at the time of the ATLAS 3 mission. This is some 37% larger than the mean 2.58 ppbv value measured by ATMOS within the same latitude zone during the Spacelab 3 flight of 29 April to 6 May 1985, consitent with an exponential growth rate of the chlorine loading in the stratosphere equal to 3.3%/yr or a linear increase of 0.10 ppbv/yr over the Spring‐1985 to Fall‐1994 time period. These findings are in agreement with both the burden and increase of the main anthropogenic Cl‐bearing source gases at the surface during the 1980s, confirming that the stratospheric chlorine loading is primarily of anthropogenic origin.

Measured stratospheric mixing ratios of HCl, ClNO3, and ClO from ATMOS and MAS are poorly reproduced by models using recommended kinetic parameters. This discrepancy is not resolved by new rates for the reactions Cl+CH4 and OH+HCl derived from weighted fits to laboratory measurements. A deficit in modeled [HCl] and corresponding overprediction of [ClNO3] and [ClO], which increases with altitude, suggests that production of HCl between 20 and 50 km is much faster than predicted from recommended rates.

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We present measurements of the latitudinal variation of nighttime O3 and H2O in the mesosphere and (for O3) lower thermosphere obtained with the Millimeter‐wave Atmospheric Sounder (MAS) instrument during the ATLAS 2 mission (8–15 April 1993). These are the first such measurements that have ever been reported. They indicate an O3 mixing ratio minimum at mid‐latitudes in the upper mesosphere, with maxima in the tropics and at high latitudes. The H2O retrievals indicate H2O mixing ratios decreasing toward the poles in both hemispheres in the upper mesosphere. We also present measurements of the diurnal variation of O3 at southern mid‐latitudes, at higher vertical resolution than has ever been reported previously. The results are generally consistent with previous measurements and modeling studies.