CF₄ and the Age of Mesospheric and Polar Vortex Air

Abstract

A chronology of tropospheric CF 4 mixing ratios is reported for the northern hemisphere. A decline of global emissions of CF 4 from 16,000 to 11,000 metric tons yr −1 is found for the periods 1978–1990 and 1992–1998, respectively. The atmospheric chronology of CF 4 is applied to determine the age of air of cryogenic air samples collected on rocket and balloon platforms. Age values of 7 years are found inside the polar vortex between 25–44 km altitude and of 11 years between 56 and 61 km altitude, which is significantly higher than predicted by most models currently used to assess the effects of high‐flying aircraft. The results suggest that the mesosphere is more isolated from below than previously believed. A comparison of age values derived from CF 4 and SF 6 relative to predicted deviations constrains the atmospheric lifetime of SF 6 to >5,000 years.