The contribution of AIRS data to the estimation of CO2 sources and sinks -: art. no. L23801

The analysis of radiance measurements from the Atmospheric Infra-Red Sounder (AIRS) has been providing the first global maps of CO2 concentrations in the cloud-free upper troposphere. This paper explores the usefulness of this data for the estimation of CO2 surface fluxes. It appears that atmospheric mixing makes the upper tropospheric CO2 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 CO2 surface fluxes. We show that latitude-dependent biases larger than a few tenths of a particle per million (ppm), at least south of 25 degrees 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.