| 02 Sep 2026
Climatology and trends in stratospheric mean age of air from correlations of multiple trace gases measured by ACE-FTS
Abstract. We develop and apply a novel method for estimating stratospheric mean age of air (AoA) from trace gases observed by the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS). The method combines SF6 with five additional long-lived tracers, N2O, CH4, CFC-11, CFC-12, and HCFC-22, and is evaluated for ACE-FTS dataset versions 3.6 and 5.2. A proof of concept using the Chemical Lagrangian Model of the Stratosphere (CLaMS) shows that the multi-tracer approach reduces the uncertainty of zonal-mean AoA by about 50 % relative to conventional methods based only on SF6 and yields AoA estimates at individual profiles with an average uncertainty of about 0.3 years. Applied to ACE-FTS data, the multi-tracer method produces smoother AoA fields and strongly suppresses noise in sparsely sampled regions compared with the conventional convolution method. Comparison with in situ AoA estimates from SF6 and CO2 generally favors the multi-tracer product, although some discrepancies remain. The method provides a precise and spatially resolved satellite-based AoA product and a promising basis for future studies of long-term changes in stratospheric circulation. Comparison of ERA5 AoA with the new satellite product indicates a slow bias in the reanalysis. The long-term AoA trend pattern over 2004–2021 shows increasing age in the Northern Hemisphere stratosphere between about 18–28 km and decreasing age in the tropics and Southern Hemisphere subtropics, largely consistent with ERA5. In particular, AoA increases in the Northern relative to the Southern Hemisphere.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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