OBSERVED VERTICAL PROFILE OF SULFUR-HEXAFLUORIDE (SF6) AND ITS ATMOSPHERIC APPLICATIONS

The vertical distribution of sulphur hexafluoride (SF6) was measured d uring a balloon-borne cryogenic air sampler experiment conducted from Hyderabad (17.5 degrees N, 78.6 degrees E) on April 16, 1994, in the a ltitude region of about 8-37 km, The profile shows a faster decrease i n its concentration in the region between the tropopause (similar to 1 7 km) and about 27 km, which is known as the transition region. Above this region the decrease rate is almost an order of magnitude less tha n in the transition layer. These results indicate very little loss of SF6 due to photochemistry in the stratosphere. Based on the reported i ncrease rate of SF6 mixing ratio at ground level and assuming that lon g-lived trace gases are transported to the stratosphere without any me asurable loss from the troposphere through the equatorial tropopause, the age of stratospheric air is estimated to vary from 1+/-0.08 years near the tropopause to 4.26+/-0.17 years above the transition layer. A tmospheric lifetime of SF6, inferred from the milling ratio correlatio ns with simultaneous measurements of N2O, and CFC-12, is computed to b e about 1937+/-432 years.