Most previous top-down global carbon monoxide (CO) budget estimates have used only concentration information and shown large differences in individual source estimates. Since CO from certain sources has a specific isotopic signature, coupling the concentration and isotope fraction information can provide a better constraint on CO source strength estimates. We simulate both CO concentration and its oxygen isotopologue C18
O in the 3-D global chemical transport model MOZART-4 and compare the results with observations. We then used a Bayesian inversion to calculate the most probable global CO budget. In the analysis, δ18
O information is jointly applied with concentration. The joint inversion results should provide more accurate and precise inversion results in comparison with CO-only inversion. Various methods combining the concentration and isotope ratios were tested to maximize the benefit of including isotope information. The joint inversion of CO and δ18
O estimated total global CO production at 2951 Tg-CO/yr in 1997, 3084 Tg-CO/yr in 1998, and 2583 Tg-CO/yr in 2004. The updated CO budget improved both the modeled CO and δ18
O. The clear improvement shown in the δ18
O implies that more accurate source strengths are estimated. Thus, we confirmed that the observation of CO isotopes provide further substantial information for estimating a global CO budget.
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