Halogenated compound identification and measurement in the troposphere and lower stratosphere

Abstract

Whole air samples were collected over the Pacific Northwest in March 1976 from a Learjet. Samples were collected on seven flights from 4.6 to 14.6 km with an average tropopause height of 10.8 km. The samples were analyzed in the laboratory for CH3Cl, CCl2F2, CCl3F, CCl4, CH3CCl3, CHCl=CCl2, CCl2F-CClF2, CCl2=CCl2, CHCl3, CClF2-CClF2, and N2O. Averaged tropospheric background concentrations are reported for these species. Stratospheric concentrations for halocarbons not previously reported are also given. The halocarbon concentration distributions as a function of altitude indicate large variability in the lower stratosphere from day to day and with altitude, while tropospheric concentrations are much more uniform. Periods of intrusion of tropospheric air into the lower stratosphere were indicated by simultaneous observations of elevated halocarbon and nitrous oxide concentrations, low ozone concentrations, and less temperature stability in the lower stratosphere. Air mass trajectory studies have traced the tropospherically influenced air parcels to previous areas consistent with positive vorticity advection, while the air masses devoid of indications of tropospheric influence have recently been transported through areas indicative of subsidence motions.