Quantification of Fossil Fuel CO2 Emissions From East Asia Using Atmospheric Observations of 14CO2

Fossil fuel CO2 emissions are the largest annual net source of CO2 to the atmosphere, and accurate quantification of these emissions is essential to furthering our understanding of the global carbon cycle. Currently, these fossil fuel CO2 emissions are estimated from economic inventories of fossil fuel use reported by governments and industry. Independent, objective methods of quantifying fossil fuel CO2 emissions are necessary to validate the inventory estimates, and have the potential to improve upon these inventories by: improving and quantifying uncertainty estimates; providing emissions estimates at smaller scales (in both space and time) than obtainable from inventories; and may be available to researchers more quickly. Measurements of the 14C content of CO2 (Δ14CO2) provide an ideal independent method of constraining fossil fuel CO2 emissions, since fossil fuel derived CO2, unlike other CO2 sources, is devoid of 14C. Several studies have demonstrated that the depletion of Δ14CO2 can be used to accurately quantify the recently-added fossil fuel CO2 component in atmospheric samples. A remaining challenge is to translate these measured fossil fuel CO2 mixing ratios into the fossil fuel CO2 flux for a given region. We approach this problem by examining time series of Δ14CO2 measurements, in combination with atmospheric transport modeling, to measure the change in fossil fuel CO2 emissions from the source region over time. This technique allows use of a relatively small number of Δ14CO2 measurements, and is less sensitive to bias in the transport model, than inversion methods. We assess the uncertainties in the estimated fossil fuel emissions, both from the measurements, and from the transport model. We use East Asia as a test region; using Δ14CO2 measurements from the NOAA/ESRL cooperative sampling network to independently measure the growth in emissions since 2004. The rapid growth in emissions from East Asia make the signal relatively easily detectable, and with China now apparently the largest fossil fuel CO2 emitting country, uncertainties or biases in the fossil fuel CO2 emission estimates for China are globally important.