Separation of biospheric and fossil fuel fluxes of CO2 by atmospheric inversion of CO2 and 14CO2 measurements: Observation System Simulations

摘要

National annual total CO emissions from combustion of fossil fuelsare likely known to within 5–10 % for most developed countries. However,uncertainties are inevitably larger (by unknown amounts) for emissionestimates at regional and monthly scales, or for developing countries. Givenrecent international efforts to establish emission reduction targets,independent determination and verification of regional and national scalefossil fuel CO emissions are likely to become increasinglyimportant. Here, we take advantage of the fact that precise measurements ofC in CO provide a largely unbiased tracer for recentlyadded fossil-fuel-derived CO in the atmosphere and present anatmospheric inversion technique to jointly assimilate observations ofCO and CO in order to simultaneously estimate fossil fuel emissions and biospheric exchange fluxes of CO. Using this method in a set of Observation System Simulation Experiments (OSSEs), we show that given the coverage of CO measurements available in 2010(969 over North America, 1063 globally), we can recover the US national totalfossil fuel emission to better than 1 % for the year and to within5 % for most months. Increasing the number of COobservations to  ∼ 5000 per year over North America, as recentlyrecommended by the National Academy of Science (NAS) (Pacala et al., 2010), we recover monthly emissions to within 5 % for all months for the US as awhole and also for smaller, highly emissive regions over which the specifieddata coverage is relatively dense, such as for the New England states or theNY-NJ-PA tri-state area. This result suggests that, given continuedimprovement in state-of-the art transport models, a measurement programsimilar in scale to that recommended by the NAS can provide for independentverification of bottom-up inventories of fossil fuel CO at theregional and national scale. In addition, we show that the dual tracerinversion framework can detect and minimize biases in estimates of thebiospheric flux that would otherwise arise in a traditional CO-onlyinversion when prescribing fixed but inaccurate fossil fuel fluxes.