The contribution of AIRS data to the estimation of CO₂ sources and sinks

The analysis of radiance measurements from the Atmospheric Infra‐Red Sounder (AIRS) has been providing the first global maps of CO 2 concentrations in the cloud‐free upper troposphere. This paper explores the usefulness of this data for the estimation of CO 2 surface fluxes. It appears that atmospheric mixing makes the upper tropospheric CO 2 concentrations rather zonal, which indicates that AIRS data inform about very broad features of the surface fluxes only. Further, such a small variability imposes a stringent constraint on the size of retrieval biases and of transport model biases for the estimation of CO 2 surface fluxes. We show that latitude‐dependent biases larger than a few tenths of a particle per million (ppm), at least south of 25°N, would harm the inversions. Significant improvements to the concentration retrieval algorithms and to the transport models are a prerequisite for the inversion of surface fluxes from AIRS.