NASA's Upper Atmosphere Research Satellite (UARS) with JPL's Microwave Limb Sounder MLS as one of its 10 instruments was launched 12 September 1991. The major objective of UARS MLS was, in response to the industrial chlorofluorocarbon threat to the ozone layer, to provide global information on chlorine monoxide (ClO), the dominant form of chlorine that destroys ozone. UARS MLS was also designed to, and did, measure stratospheric ozone and water vapor. The following additional measurements were obtained: stratospheric temperature, upper tropospheric water vapor, cloud ice water content, stratospheric HNO3, volcanic SO2 injected into the stratosphere, temperature variances associated with atmospheric gravity waves, and stratospheric CH3CN.

UARS MLS generally provided daily measurements from 29 September through 15 March 1994 (although stratospheric water vapor measurements ceased on 15 April 1993). After 15 March 1994 the measurements became increasingly sparse in order to conserve lifetime of the MLS antenna scan mechanism and UARS power. The last data were obtained on 25 August 2001.