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We investigate different methods for estimating anthropogenic CO2 usingmodeled continuous atmospheric concentrations of CO2 alone, as well asCO2 in combination with the surrogate tracers CO, δ13C(CO2) and Δ14C(CO2). These methods areapplied at three hypothetical stations representing rural, urban andpolluted conditions. We find that, independent of the tracer used, anobservation-based estimate of continuous anthropogenic CO2 is not yetfeasible at rural measurement sites due to the low signal-to-noise ratio ofanthropogenic CO2 estimates at such settings. The tracers δ13C(CO2) and CO provide an accurate possibility to determineanthropogenic CO2 continuously, only if all CO2 sources in thecatchment area are well characterized or calibrated with respect to theirisotopic signature and CO to anthropogenic CO2 ratio. We test differentcalibration strategies for the mean isotopic signature and CO to CO2ratio using precise Δ14C(CO2) measurements onmonthly integrated as well as on grab samples. For δ13C(CO2), a calibration with annually averaged 14C(CO2)grab samples is most promising, since integrated sampling introduces largebiases into anthropogenic CO2 estimates. For CO, these biases aresmaller. The precision of continuous anthropogenic CO2 determinationusing δ13C(CO2) depends on measurement precision ofδ13C(CO2) and CO2, while the CO method is mainlylimited by the variation in natural CO sources and sinks. At present,continuous anthropogenic CO2 could be determined using the tracersδ13C(CO2) and/or CO with a precision of about 30 %, amean bias of about 10 % and without significant diurnal discrepancies.Hypothetical future measurements of continuous Δ14C(CO2)with a precision of 5 ‰ are promising for anthropogenicCO2 determination (precision ca. 10–20 %) but are not yet available. The investigated tracer-based approaches open the door to improving,validating and reducing biases of highly resolved emission inventories usingatmospheric observation and regional modeling

atmospheric chemistry and physics

Estimation of continuous anthropogenic CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;: model-based evaluation of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, CO, δ&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C(CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) and Δ&amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C(CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) tracer methods