Determination of triple oxygen isotope composition of tropospheric CO2

The isotopic composition of carbon dioxide originating at the surface is modified in the stratosphere. Given that the only source of oxygen anomaly (Δ¹⁷O = δ¹⁷O - 0.516×δ¹⁸O > 0) is in the stratosphere, such isotopic signal provides a powerful tracer for studying biogeochemical cycles involving carbon dioxide. In addition to the exiting fluorination method that can achieve a precision as high as ~0.1 per mil, we improved a previously proposed technique, CeO₂ + CO₂ equilibrium at high temperature, to a precision of ~0.1 per mil and better. Such improvement allows us monitor the changes of biogeochemical CO₂ in detail. We successfully measure Δ¹⁷O in near surface carbon dioxide. Implications for constraining the sources and sinks of CO₂ using its isotope signature are discussed