Tracer correlations in the northern high latitude lowermost stratosphere: Influence of cross-tropopause mass exchange

We present an analysis of trace gas correlations in the lowermost stratosphere. In-situ aircraft measurements of CO, N2O, NOy and O-3 Obtained during the STREAM 1997 winter campaign, have been used to investigate the role of cross-tropopause mass exchange on tracer-tracer relations. At altitudes several;kilometers above the local tropopause, undisturbed stratospheric air was found with NOy/NOy* ratios close to unity, NOy/O-3 about 0.003 - 0.006 and CO mixing ratios as low as 20 ppbv (NOy* is a proxy for total reactive nitrogen derived from NOy-N2O relations measured in the stratosphere). Mixing of tropospheric-air into the lowermost stratosphere has been identified by enhanced ratios of NOy/NOy* and NOy/O-3, and from scatter plots of CO versus O-3. The enhanced NOy/O-3 ratio in the lowermost stratospheric mixing zone points to a reduced efficiency of O-3 formation from aircraft NOx emissions.