Balloon‐borne observations of midlatitude fluorine abundance

Abstract

Volume mixing ratio profiles of fluorine source gases (CF2Cl2, CFCl3, CF2ClCFCl2, CHF2Cl, CF4, and SF6) and reservoir gases (COF2 and HF) have been derived from a series of high‐resolution infrared solar spectra recorded by the Jet Propulsion Laboratory MkIV interferometer during a September 1993 balloon flight from Fort Sumner, New Mexico (34°N, 104°W). The total fluorine budget over the 5‐ to 38‐km altitude range has been evaluated by adding these individual measured profiles to modeled predictions for the unmeasured gas COFCl (considered to be at most 6% of the total fluorine budget). The results indicate a steady decrease of total fluorine, with increasing altitude, from a tropospheric value of about 1.82 parts per billion by volume (ppbv) to 1.48 ppbv at 38 km. The latter value, made up entirely of the reservoir species, is commensurate with tropospheric concentrations of fluorine reported in the late 1980s and with time‐dependent two‐dimensional model predictions (1.45 ppbv). Therefore the “age” of the stratospheric air mass estimated from the MkIV fluorine budget is 4–5 years, in agreement with model simulations (≈6 years) and recent ATMOS measurements.