Radiocarbon observations in atmospheric CO2: determining fossil fuel CO2 over Europe using Jungfraujoch observations as background.

. Attributing observed CO2 variations to human or natural cause is critical to deducing and tracking emissions from observations. We have used in situ CO2, CO, and planetary boundary layer height (PBLH) measurements recorded during the CalNex-LA (CARB et al., 2008) ground campaign of 15 May–15 June 2010, in Pasadena, CA, to deduce the diurnally varying anthropogenic component of observed CO2 in the megacity of Los Angeles (LA). This affordable and simple technique, validated by carbon isotope observations and WRF-STILT (Weather Research and Forecasting model – Stochastic Time-Inverted Lagrangian Transport model) predictions, is shown to robustly attribute observed CO2 variation to anthropogenic or biogenic origin over the entire diurnal cycle. During CalNex-LA, local fossil fuel combustion contributed up to ~50% of the observed CO2 enhancement overnight, and ~100% of the enhancement near midday. This suggests that sufficiently accurate total column CO2 observations recorded near midday, such as those from the GOSAT or OCO-2 satellites, can potentially be used to track anthropogenic emissions from the LA megacity.

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Diurnal tracking of anthropogenic CO 2 emissions in the Los Angeles basin megacity during spring 2010

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

Inferring high-resolution fossil fuel CO 2 records at continental sites from combined 14 CO 2 and CO observations

A 7-year-long data set of integrated high-precision 14 CO 2 observations combined with occasional hourly 14 CO 2 flask data from the Heidelberg sampling site is presented. Heidelberg is located in the highly populated and industrialized upper Rhine valley in southwestern Germany. The 14 CO 2 data are used in combination with hourly carbon monoxide (CO) observations to estimate regional hourly fossil fuel CO 2 (ΔFFCO 2 ) mixing ratios. We investigate three different 14 C calibration schemes to calculate ΔFFCO 2 : (1) the long-term median ΔCO/ΔFFCO 2 ratio of 14.6 ppb ppm -1 (mean: 15.5 ± 5.6 ppb ppm -1 ), (2) individual (2-)week-long integrated ΔCO/ΔFFCO 2 ratios, which take into account the large week-to-week variability of ±5.6 ppb ppm -1 (1σ; interquartile range: 5.5 ppb ppm -1 ), and (3) a calibration which also includes diurnal changes of the ΔCO/ΔFFCO 2 ratio. We show that in winter a diurnally changing ΔCO/ΔFFCO 2 ratio provides a much better agreement with the direct 14 C-based hourly ΔFFCO 2 estimates whereas summer values are not significantly improved with a diurnal calibration. Using integrated 14 CO 2 samples to determine weekly mean ΔCO/ΔFFCO 2 ratios introduces a bias in the CO-based ΔFFCO 2 estimates which can be corrected for with diurnal grab sample data. Altogether our 14 C-calibrated CO-based method allows determining ΔFFCO 2 at a semi-polluted site with a precision of approximately ±25%. DOI: 10.1111/j.1600-0889.2010.00477.x

https://www.tandfonline.com/doi/pdf/10.1111/j.1600-0889.2010.00477.x

Implication of weekly and diurnal 14C calibration on hourly estimates of CO‐based fossil fuel CO2 at a moderately polluted site in southwestern Germany

We analyzed the magnitude, the trends and the uncertainties of fossil-fuel CO2 emissions in the European Union 25 member states (hereafter EU-25), based on emission inventories from energy-use statistics. The stability of emissions during the past decade at EU-25 scale masks decreasing trends in some regions, offset by increasing trends elsewhere. In the recent 4 years, the new Eastern EU-25 member states have experienced an increase in emissions, reversing after a decade-long decreasing trend. Mediterranean and Nordic countries have also experienced a strong acceleration in emissions. In Germany, France and United Kingdom, the stability of emissions is due to the decrease in the industry sector, offset by an increase in the transportation sector. When four different inventories models are compared, we show that the between-models uncertainty is as large as 19% of the mean for EU-25, and even bigger for individual countries. Accurate accounting for fossil CO2 emissions depends on a clear understanding of system boundaries, i.e. emitting activities included in the accounting. We found that the largest source of errors between inventories is the use of distinct systems boundaries (e.g. counting or not bunker fuels, cement manufacturing, nonenergy products). Once these inconsistencies are corrected, the between-models uncertainty can be reduced down to 7% at EU-25 scale. The uncertainty of emissions at smaller spatial scales than the country scale was analyzed by comparing two emission maps based upon distinct economic and demographic activities. A number of spatial and temporal biases have been found among the two maps, indicating a significant increase in uncertainties when increasing the resolution at scales finer than ~200 km. At 100 km resolution, for example, the uncertainty of regional emissions is estimated to be 60 g C m^(-2) yr^(-1), up to 50% of the mean. The uncertainty on regional fossil-fuel CO2 fluxes to the atmosphere could be reduced by making accurate ^(14)C measurements in atmospheric CO2, and by combining them with transport models.

The European carbon balance. Part 1: fossil fuel emissions

Carbon monoxide (CO), carbon dioxide (CO2), and radiocarbon (14CO2) measurements have been made in Heidelberg from 2001 to 2004 in order to determine the regional fossil fuel CO2 component and to investigate the application of CO as a quantitative tracer for fossil fuel CO2 (CO2(foss)). The observations were compared with model estimates simulated with the regional transport model REMO at 0.5° × 0.5° resolution in Europe for 2002. These estimates are based on two available emissions inventories for CO and CO2(foss) and simplified atmospheric chemistry of CO. Both emissions inventories appear to overestimate fossil fuel emissions in the Heidelberg catchment area, in particular in summer and autumn by up to a factor of 2. Nevertheless, during meteorological conditions with high local source influence the CO/CO2(foss) emission ratios compared well with the observed atmospheric CO/CO2(foss) ratios. For a larger catchment area of several 100 km the observed CO/CO2(foss) ratio compared within better than 25% with the ratios derived from model simulations that take the transport from the sites of emission to the measurement station into account. Non-fossil-fuel CO emissions, production by volatile organic compounds, and oxidation, as well as soil uptake, turned out to add significant uncertainty to the application of CO as a quantitative fossil fuel CO2 surrogate tracer, so that 14CO2 measurements seem to be indispensable for reliable estimates of fossil fuel CO2 over the European continent. (Less)

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JD006966

Hartwig Schroeder

Papers

Carbon monoxide : a quantitative tracer for fossil fuel CO2?