Using stable isotope of measurements of carbon monoxide for constraining short- and long-term changes in its global budget and atmospheric chemistry

Carbon monoxide (CO) is an important indirect greenhouse gas, plays a key intermediate role in the cycling of carbon compounds in the atmosphere and via these reactions affects the atmospheric oxidation capacity. Its sources and sinks can be (partially) distinguished with isotope measurements, but extensive observations of CO isotopic composition are sparse. A network of independent global observatories monitored 𝛿¹³C_CO and 𝛿 ¹⁸O_CO at the turn of the 21^st century. Since this time, the sole continuous monitoring of CO isotopic composition has been carried out at Baring Head, New Zealand. Starting in 2023, as part of the ISAMO project, we have resumed regular measurements of 𝛿¹³C_CO and 𝛿 ¹⁸O_CO  at seven global monitoring stations, with a focus on the tropical Atlantic. The goal of ISAMO is to better constrain the proposed pathway of methane removal via chlorine radicals that can be released photochemically from mixed mineral dust - salt aerosols. Here we use the new and existing CO isotope data together with model simulations to derive empirical constraints for the production rate of CO from the CH4 + Cl reaction. In addition, we will demonstrate how CO isotope measurements can be used to constrain long-term, and episodic, changes in the global and regional CO budget, arguing for sustaining such measurements at globally distributed locations.