Airborne in-situ measurements of vertical, seasonal and latitudinal distributions of carbon dioxide over Europe

Airborne in-situ observations of carbon dioxide (CO2) were made during 7 intensive measurement campaigns between November 2001 and April 2003 as part of the SPURT project. Vertical profiles and latitudinal gradients in the upper troposphere/lowermost stratosphere were measured along the western shore of Europe from the subtropics to high northern latitudes during different seasons. In the boundary layer, CO2 exhibits a strong seasonal cycle with the maximum mixing ratios in winter and minimum values in summer, reflecting the strength of CO2 exchange with vegetation. Seasonal variations are strongest in high latitudes and propagate to the free troposphere and lowermost stratosphere, although with reduced amplitude. In the lowermost stratosphere, the CO2 seasonal cycle is phase-shifted relative to the free troposphere by approximately 3 months, with highest mixing ratios during the summer. Modelling studies support the interpretation that altitude gradients of CO2 are likely due to stratosphere-troposphere-transport.