The Atmospheric Chemistry Experiment–Fourier Transform Spectrometer (ACE-FTS) on SCISAT-1 and Microwave Limb Sounder (MLS) on NASA’s Aura satellite have contributed significantly to understanding the impacts of human activities on the stratospheric ozone layer. The two-decade-long data record from these instruments has allowed quantification of ozone depletion caused by human-released ozone-depleting substances, the effects of extreme natural events like major volcanic eruptions including Hunga in 2022, and events amplified by human-caused climate change such as wildfires that inject material into the stratosphere, as happened over Australia in early 2020. The Aura platform is nearing the end of its operational lifetime, and SCISAT-1 is over 20 years old. Their decommissioning will cause a substantial gap in the measurement of critical atmospheric components, including water vapor, inorganic chlorine species, and tracers of stratospheric transport. This upcoming “data desert” poses significant challenges for monitoring the recovery of the ozone layer and assessing the effects on stratospheric composition of future extreme events, threats posed by increases in space debris from satellite burn-up, and the possible injection of stratospheric aerosol to mitigate global warming. The lack of confirmed future missions that can provide daily near-global profile measurements of stratospheric composition highlights the need for observational strategies to bridge this impending gap. This paper discusses the essential role of ACE-FTS and MLS in advancing our understanding of the stratosphere, the impact of data loss after the cessation of one or both instruments, and the urgency of developing strategies for mitigating the impact of these observational losses at a time marked by dramatic changes in the stratosphere due to human and natural factors.

This overview paper highlights the successes of the Ozone Monitoring Instrument (OMI) on board the Aura satellite spanning a period of nearly 14 years. Data from OMI has been used in a wide range of applications and research resulting in many new findings. Due to its unprecedented spatial resolution, in combination with daily global coverage, OMI plays a unique role in measuring trace gases important for the ozone layer, air quality, and climate change. With the operational very fast delivery (VFD; direct readout) and near real-time (NRT) availability of the data, OMI also plays an important role in the development of operational services in the atmospheric chemistry domain.