Estimation of continuous anthropogenic COsub2/sub: model-based evaluation of COsub2/sub, CO, ?′sup13/supC(COsub2/sub) and ??sup14/supC(COsub2/sub) tracer methods

摘要

pstrongAbstract./strong We investigate different methods for estimating anthropogenic COsub2/sub using modeled continuous atmospheric concentrations of COsub2/sub alone, as well as COsub2/sub in combination with the surrogate tracers CO, δsup13/supC(COsub2/sub) and ??sup14/supC(COsub2/sub). These methods are applied at three hypothetical stations representing rural, urban and polluted conditions. We find that, independent of the tracer used, an observation-based estimate of continuous anthropogenic COsub2/sub is not yet feasible at rural measurement sites due to the low signal-to-noise ratio of anthropogenic COsub2/sub estimates at such settings. The tracers δsup13/supC(COsub2/sub) and CO provide an accurate possibility to determine anthropogenic COsub2/sub continuously, only if all COsub2/sub sources in the catchment area are well characterized or calibrated with respect to their isotopic signature and CO to anthropogenic COsub2/sub ratio. We test different calibration strategies for the mean isotopic signature and CO to COsub2/sub ratio using precise ??sup14/supC(COsub2/sub) measurements on monthly integrated as well as on grab samples. For δsup13/supC(COsub2/sub), a calibration with annually averaged sup14/supC(COsub2/sub) grab samples is most promising, since integrated sampling introduces large biases into anthropogenic COsub2/sub estimates. For CO, these biases are smaller. The precision of continuous anthropogenic COsub2/sub determination using ?′sup13/supC(COsub2/sub) depends on measurement precision of ?′sup13/supC(COsub2/sub) and COsub2/sub, while the CO method is mainly limited by the variation in natural CO sources and sinks. At present, continuous anthropogenic COsub2/sub could be determined using the tracers ?′sup13/supC(COsub2/sub) and/or CO with a precision of about 30 %, a mean bias of about 10 % and without significant diurnal discrepancies. Hypothetical future measurements of continuous ??sup14/supC(COsub2/sub) with a precision of 5 ‰ are promising for anthropogenic COsub2/sub determination (precision ca. 10a??20 %) but are not yet available. The investigated tracer-based approaches open the door to improving, validating and reducing biases of highly resolved emission inventories using atmospheric observation and regional modeling./p.