Contribution of tropospheric SO2 to the stratospheric aerosol layer

Measurements of SO2 mixing ratio in the upper troposphere and lower stratosphere have been performed with a sensitive chemiluminescence method which permits the detection of atmospheric SO2 traces below 10 pptv. Results of 9 aircraft ascents over Europe from 1978-1980 are reported. It is shown that the meteorological conditions at the tropopause level have an important influence on the observed SO2 mixing ratio. The weak vertical SO2 gradients in the upper troposphere suggest only a small flux of tropospheric SO2 into the stratosphere. Furthermore, increasing SO2 mixing ratios within the first kilometers of the stratosphere give strong support to a stratospheric SO2 source due to the oxidation of organic sulfur compounds (COS, CS2). SO2 measurements are discussed in the light of improved 1 D models concerning the stratospheric sulfur budget. The results clearly show that tropospheric SO2 is of only minor importance for the non-volcanic formation of the stratospheric aerosol. (IFU)