CO data can provide a powerful constraint on fire fluxes, supporting more accurate estimation of biospheric CO₂ fluxes. We converted CO fire flux into CO₂ fire prior, which is then used to adjust CO₂ respiration. We applied this to two other fire flux products. CO₂ inversions constrained by satellites or in situ data are then performed. Results show larger variations among the data assimilated than across the priors, but tropical flux from in situ inversions is sensitive to priors.