Measurements of concentration, 13C/12C and 18O/16O ratios of tropospheric carbon dioxide over Switzerland

In 1982, we collected air sample profiles approximately monthly from aircraft at altitudes up to about 7 km and analyzed them for CO2 concentration and stable isotope composition. The following seasonally detrended mean values were obtained per 1 January, 1982: 338 ppm, δ13C=-7.72%, δ18O = -0.6% (versus PDB); isotopic results are corrected for N2O contribution. CO2 results are discussed in terms of vertical eddy diffusion and of a mean annual vertical flux. Assuming a two-component mixture between background air and biospheric CO2, δ13C of the biospheric component is -26.2R%, in good agreement with other northern hemisphere results. δ18O varies seasonally, but with relatively much scatter. The oxygen isotopic composition of CO2 is determined by exchange with vegetation, soils and ocean; these processes are discussed in detail.