On aggregation errors in atmospheric transport inversions

This paper explores the consequences of resolution of surface fluxes on syn thesis inversions of carbon dioxide. Synthesis inversion divides the Earth' s surface into a set of regions and solves for the magnitudes of fluxes fro m these regions, The regions are generally quite large. By considering an i nversion performed at the resolution of the underlying transport model we s how that the aggregation to large regions can cause significant differences in the fnal results, with errors of the same order of magnitude as the flu xes themselves. Using a simple model, we derive an algorithm to reduce this error. This algorithm accounts for the extra data uncertainty that is caus ed by uncertainty in the small-scale flux components. In the spatial synthe sis inversion this extra data uncertainty reaches a maximum value of 3.5 pp mv. Accounting for it can halve the aggregation error. We provide suggestio ns for dealing with this problem when high-resolution inversions are not fe asible.