Measurements of CO during STREAM III and Polstar I

Obersations of trace gases like CO and N2O in the lower stratosphere provide information about the origin of the probed air. Expecially correlations of tracers with different chemical lifetimes can be used to differentiate between transport processes and photochemistry. CO has its major sources in the planetary boundary layer, while the photochemical degradation of CH4 and NMHC by OH constitutes additional sources in the freee troposphere and lower stratosphere [1]. Oxidation by OH is the major sink for CO in the atomosphere yielding a mean lifetime of approximately there months for CO in the lower stratosphere. Troposhperic CO exhibits a latitude dependent seasonal cycle, with a maximum amplitude of about 100 ppbv [2] at high latitudes decreasing towards equatorial regions. N2O has a mean photochemical lifetime of approximately 110 years. Above the tropopause N2O concentrations decrease with altitude so that N2O can be used as an alternative geight scale independent of short term disp lacements of air parcels