Global observation of the stratospheric air age

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Collections of stratospheric air samples have been carried out over Japan, the eastern equatorial Pacific, and Syowa station, Antarctica, using a balloon-borne cryogenic sampler. The air samples were analyzed for various gas concentrations, such as CO2, CH4, N2O, and SF6, and their isotopes. The CO2 and SF6 concentrations increased from year to year at all heights in the stratosphere. The CO2-age and SF6-age of stratospheric air were estimated by comparing the observed concentrations with the CO2 and SF6 variations at Mauna Loa. The average change rate of the mean age in the mid-stratosphere was 0.04 (+-0.01) years/year. Recent model studies suggest that the global warming should have strengthened the Brewer-Dobson circulation by an enhanced mass flux from the tropical troposphere into the stratosphere, which should result decreasing of the mean age. However, our result shows no decreasing trend of the mean age in the mid-stratosphere for the last 25 years.