We observed a plume of air highly enriched in carbon monoxide and particles in the stratosphere at altitudes up to 15.8 km. It can be unambiguously attributed to North American forest fires. This plume demonstrates an extra‐tropical direct transport path from the planetary boundary layer several kilometers deep into the stratosphere, which is not fully captured by large‐scale atmospheric transport models. This process indicates that the stratospheric ozone layer could be sensitive to changes in forest burning associated with climatic warming.

[1] The present paper deals with a boundary layer budgeting method which makes use of observations from various in situ and remote sensing instruments to infer regional average net ecosystem exchange (NEE) of CO 2 . Measurements of CO 2 within and above the atmospheric boundary layer (ABL) by in situ sensors, in conjunction with a precise knowledge of the change in ABL height by lidar and radiosoundings, enable to infer diurnal and seasonal NEE variations. Near-ground in situ CO measurements are used to discriminate natural and anthropogenic contributions of CO 2 diurnal variations in the ABL. The method yields mean NEE that amounts to 5 mmol m À2 s À1 during the night and À20 mmol m À2 s À1 in the middle of the day between May and July. A good agreement is found with the expected NEE accounting for a mixed wheat field and forest area during winter season, representative of the mesoscale ecosystems in the Paris area according to the trajectory of an air column crossing the landscape. Daytime NEE is seen to follow the vegetation growth and the change in the ratio diffuse/direct radiation. The CO 2 vertical mixing flux during the rise of the atmospheric boundary layer is also estimated and seems to be the main cause of the large decrease of CO 2 mixing ratio in the morning. The outcomes on CO 2 flux estimate are compared to eddy-covariance measurements on a barley field. The importance of various sources of error and uncertainty on the retrieval is discussed. These errors are estimated to be less than 15%; the main error resulted from anthropogenic emissions.Citation: Gibert, F., M. Schmidt, J. Cuesta, P. Ciais, M. Ramonet, I. Xueref, E. Larmanou, and P. H. Flamant (2007), Retrieval of average CO 2 fluxes by combining in situ CO 2 measurements and backscatter lidar information,