Independent evaluation of point source fossil fuel CO 2 emissions to better than 10

The 1,000 largest power plants comprise 22% of total global fossil fuel CO 2 emissions, making them an obvious target for regulating and reducing emissions. The success of existing and upcoming regulations and emission trading schemes requires reliable monitoring and verification of emissions, preferably using independent, objective evaluation to establish trust and transparency. However, such methodology has thus far been elusive, and emissions reporting currently relies solely on self-reported “bottom-up” inventory data. We demonstrate a method using time-integrated atmospheric observations and modeling to reliably quantify fossil fuel CO 2 emissions from point sources to within 10%. This level of uncertainty is a marked improvement over current ∼20% uncertainties for individual power plants and allows independent evaluation of reported emissions. Independent estimates of fossil fuel CO 2 (CO 2 ff) emissions are key to ensuring that emission reductions and regulations are effective and provide needed transparency and trust. Point source emissions are a key target because a small number of power plants represent a large portion of total global emissions. Currently, emission rates are known only from self-reported data. Atmospheric observations have the potential to meet the need for independent evaluation, but useful results from this method have been elusive, due to challenges in distinguishing CO 2 ff emissions from the large and varying CO 2 background and in relating atmospheric observations to emission flux rates with high accuracy. Here we use time-integrated observations of the radiocarbon content of CO 2 ( 14 CO 2 ) to quantify the recently added CO 2 ff mole fraction at surface sites surrounding a point source. We demonstrate that both fast-growing plant material (grass) and CO 2 collected by absorption into sodium hydroxide solution provide excellent time-integrated records of atmospheric 14 CO 2 . These time-integrated samples allow us to evaluate emissions over a period of days to weeks with only a modest number of measurements. Applying the same time integration in an atmospheric transport model eliminates the need to resolve highly variable short-term turbulence. Together these techniques allow us to independently evaluate point source CO 2 ff emission rates from atmospheric observations with uncertainties of better than 10%. This uncertainty represents an improvement by a factor of 2 over current bottom-up inventory estimates and previous a