University of Colorado iodine data measured in the UTLS aboard the NSF-NCAR GV aircraft during two field campaigns: Tropical Ocean tRoposphere Exchange of Reactive Halogen Species and Oxygenated VOC (TORERO), Eastern Pacific Ocean CONvective Transport of Active Species in the Tropics (CONTRAST), Western Pacific Ocean References: Volkamer et al., 2015 (doi:10.5194/amt-8-2121-2015), Pan et al., 2016 (doi:10.1175/BAMS-D-14-00272.1) Principal Investigator: Prof. Rainer Volkamer (rainer.volkamer@colorado.edu) Data prepared by Dr. Theodore K. Koenig (theodore.koenig@colorado.edu) This file contains data as presented in Koenig et al., 2020 (doi:10.1073/pnas.1916828117) Iodine monoxide (IO) is measured by the CU AMAX-DOAS instrument following methods described in Dix et al., 2016 (doi:10.5194/amt-9-5655-2016) with minor adaptations. The uncertainty in the IO mixing ratio for these measurements in the UTLS is better than reported in Dix et al., namely, it is 20% of the measured mixing ratio but not better than 0.03 ppt. These components should be added in quadrature: err(IO) = sqrt( (0.2*IO)^2 + 0.03^2) IO/Iy is the ratio of iodine monoxide to total gas-phase iodine (Iy) modeled using the CU box-model constrained by measured temperature, pressure, chemical concentrations, particle size distributions, and photolysis frequencies. The uncertainty is estimated as 30% of the ratio, incl. errors in the calibration of in-situ and remote sensing data, and accounting for differences in the spatial scales. The inferred Iy is based on the measured IO and modeled IO/Iy. The uncertainty in Iy is propagated from the uncertainties in IO and that of IO/Iy.