Atmospheric column-averaged mole fractions of carbon dioxide at 53 aircraft measurement sites

Atmospheric column-averaged mole fractions of carbon dioxide (XCO ₂) at 53 locations around the world were derived from aircraft measurements covering the altitude range of about 1-10 km. We used CO ₂ vertical profile measurements from three major carbon cycle programs, a global climatological data set of air number density profiles and tropopause height for calculating XCO₂ for the period of 2007-2009. Vertical profiles of the CO₂ mixing ratio are complemented by tall tower data up to 400m from the earth's surface and by simulated profiles in the stratosphere from a chemistry-transport model. The amplitude of the seasonal cycle of calculated XCO₂ values shows clear latitudinal dependence, and the amplitude decreases from about 10 ppm at high latitudes in the Northern Hemisphere to at most 2 ppm in the tropics and the Southern Hemisphere. The uncertainties of XCO₂ were estimated from assumptions about CO ₂ profiles for each flight. Typically, uncertainties were less than 1 ppm; thus, this data set is within the level of uncertainty needed for primary validation of XCO₂ measurements by the Greenhouse gases Observing SATellite (GOSAT) and by future satellite missions for monitoring greenhouse gases.