CO ₂ Isotopologues From the ACE Satellite

Carbon dioxide isotopologues have been studied thoroughly in the troposphere. In the stratosphere, the minor oxygen CO 2 isotopologues have anomalous abundances due to their exchange reactions with isotopically fractionated ozone, differentiating them from tropospheric CO 2 . Previously a model predicted that this anomalous isotopic abundance continues into the mesosphere but lacked verification from experimental observations. Here we use the Atmospheric Chemistry Experiment Fourier Transform Spectrometer which records infrared transmittance spectra of the Earth's limb from low Earth orbit using solar occultation. These infrared spectra provide measurements of global CO 2 isotopologue volume mixing ratios (VMRs) from the upper troposphere to the lower thermosphere. Data for the O 13 CO, 17 OCO and 18 OCO isotopologues are presented, including seasonal altitude‐latitude VMR distributions. The role of photolysis in the upper atmosphere for 17 OCO and 18 OCO fractionation has been analyzed and found to be “mass independent.”