Simulations of atmospheric CO2 and δ13C-CO2 compared to real-time observations at the high altitude station Jungfraujoch

<p>Evaluating atmospheric transport simulations against observations helps refining bottom-up estimates of greenhouse gas fluxes and identifying gaps in our understanding of regional and category-specific contributions to atmospheric mole fractions. This insight is critical in the efforts to mitigate anthropogenic environmental impact. Beside total mole fractions, stable isotope ratios provide further constraints on source-sink processes [1-3].</p><p>Here, we present two receptor-oriented model simulations for carbon dioxide (CO<sub>2</sub>) mole fraction and δ<sup>13</sup>C-CO<sub>2</sub> stable isotope ratios for a nine year period (2009-2017) at the High Altitude Research Station Jungfraujoch (Switzerland, 3580 m asl). The model simulations of CO<sub>2</sub> were performed on a 3-hourly time-resolution with two backward Lagrangian particle dispersion models driven by two different numerical weather forecast fields: FLEXPART-COSMO and STILT-ECMWF. Anthropogenic CO<sub>2</sub> fluxes were based on the EDGAR v4.3 emissions inventory aggregated into 14 source categories representing fossil and biogenic fuel uses as well as emissions from cement production. Biospheric CO<sub>2</sub> fluxes representing the photosynthetic uptake and respiration of 8 plant functional types were based on the Vegetation Photosynthesis and Respiration Model (VPRM). The simulated CO<sub>2</sub> emissions per source and sink category were weighted with category-specific δ<sup>13</sup>C-CO<sub>2</sub> signatures from published experimental studies. Background CO<sub>2</sub> values at the boundaries of both model domains were taken from global model simulations and the corresponding δ<sup>13</sup>C-CO<sub>2</sub> values were constructed as suggested in Ref. [3]. We compare the simulations to a unique data set of continuous in-situ observations of CO<sub>2</sub> mole fractions and δ<sup>13</sup>C-CO<sub>2</sub> stable isotope ratios by quantum cascade laser absorption spectroscopy as described in previous work [1, 4-5], available for the whole nine year period at the site.</p><p>The simulated atmospheric CO<sub>2</sub> and δ<sup>13</sup>C-CO<sub>2</sub> time-series are in good agreement with the observations and capture the observed variability at the models' 3-hourly time-resolution. This allows for an in-depth evaluation of the contribution of different CO<sub>2</sub> emission sources and for an allocation of source regions when Jungfraujoch is influenced by air masses from the planetary boundary layer. In brief, the receptor-oriented model simulations suggest that anthropogenic CO<sub>2</sub> contributions are primarily of fossil origin (90%). Anthropogenic emissions contribute between 60% in February, and 20% in July/August, to the CO<sub>2</sub> enhancements observed at Jungfraujoch. The remaining fraction is due to biosphere respiration, which thus largely dominates emissions during the summer season. However, intense photosynthetic CO<sub>2</sub> uptake during June, July and August roughly outweighs CO<sub>2</sub> contributions from anthropogenic activities and biosphere respiration at JFJ.</p><p> </p><p> </p><p>REFERENCES</p><p>[1] Tuzson et al., 2011. ACP, 11, 1685</p><p>[2] Röckmann et al., 2016. ACP, 16, 10469</p><p>[3] Vardag et al., 2016. Biogeosciences, 13, 4237</p><p>[4] Tuzson et al., 2008. Appl. Phys. B, 92, 451</p><p>[5] Sturm et al., 2013. AMT 6, 1659</p>