Inferring high-resolution fossil fuel CO₂ records at continental sites from combined ¹⁴CO₂ and CO observations

An uncertainty estimate of a purely observational approach to derive hourly regional fossil fuel CO 2 offsets (ΔCO 2 (foss)) at continental CO 2 monitoring sites is presented. Weekly mean 14 C-based fossil fuel CO 2 mixing ratios and corresponding regional CO offsets (ΔCO) are proposed to determine weekly mean ΔCO/ΔCO 2 (foss) ratios in order to derive hourly ΔCO 2 (foss) mixing ratios from hourly ΔCO measurements. Respective regional model estimates of CO and CO 2 (foss) are applied to test this approach and obtain root mean square errors of the correspondingly determined regional hourly fossil fuel CO 2 component. The method is further validated with campaign-based observations in Heidelberg. The uncertainty of the proposed method turns out to increase with decreasing fossil fuel CO 2 fraction ranging from about 15% up to 40% for continental Europe. Together with the uncertainty of the ΔCO/ΔCO 2 (foss) ratio, which is determined by the precision of the 14 CO 2 measurement, this method is still more accurate and precise than any model-based approach. DOI: 10.1111/j.1600-0889.2006.00244.x