We present a diagnostics, implemented in an Earth-System Model, which keeps track of the contribution of source categories (mainly emission sectors) to various concentrations (O3
). For the first time, it takes into account chemically competing effects, e.g., the competition between ozone precursors in the production of ozone. We show that the results are in-line with results from other tagging schemes and provide plausibility checks for OH and HO2
, which have not previously been tagged.