Trace gas profiles to 3000 m over Antarctica

During October–December, 1980 air samples collected on 13 helicopter flights between 30 and 3000 m above the Ross Ice Shelf, Antarctica were analyzed in McMurdo for N 2O and the halocarbons, F-11, F-12, CCl 4 and CH 3CCl 3 using electron capture gas chromatography. The average profile showed highest concentrations below 150 m for F-12, CCl 4 and N 2O and lowest concentrations for all compounds between 360 and 1800 m. Average profiles differed when flights were classified on the basis of low-level inversion conditions, the magnitude of the temperature lapse rate, or the direction of upper level winds. These differences in trace chemical profiles above 200 m are postulated to result from a combination of mid latitude air mass advection and subsequent dilution over Antarctica with stratospheric air. Lower boundary layer gradients may indicate a surface source from an unknown physical enrichment process.