MOZAIC data collected at cruise altitude (between 8 and 12 km), north of 25°N have been referenced to the tropopause altitude (defined as a 30 hPa thick layer centered around the 2 pvu surface) to assess O3 and CO distributions in the UT (within 60 hPa below the tropopause) and in the LS (starting from 45 hPa above the tropopause) independently. Further details may be found in Thouret et al., 2006.
UT-These seasonal distributions show a spring maximum at northern midlatitudes, extending till summer over Eastern Asia and northern Canada because of boreal fires. Generally, high CO concentrations in the UT are recorded at the time of year over regions where intense biomass burning is occuring.
(click on image to enlarge)
LS-CO concentrations are very low at this altitude, globally less than 55 ppbv. It is interesting to note the quasi absence of seasonal cycle, in contrast to the UT.