Simulations of atmospheric CO2 and &#948;13C-CO2 compared to real-time observations at the high altitude station Jungfraujoch
Authors: Pieber Simone M. , Tuzson Béla , Henne Stephan , Karstens Ute , Brunner Dominik , Steinbacher Martin , Emmenegger Lukas 
Published: March 2020

&lt;p&gt;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].&lt;/p&gt;&lt;p&gt;Here, we present two receptor-oriented model simulations for carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) mole fraction and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; emissions per source and sink category were weighted with category-specific &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; signatures from published experimental studies. Background CO&lt;sub&gt;2&lt;/sub&gt; values at the boundaries of both model domains were taken from global model simulations and the corresponding &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; values were constructed as suggested in Ref. [3]. We compare the simulations to a unique data set of continuous in-situ observations of CO&lt;sub&gt;2&lt;/sub&gt; mole fractions and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; 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.&lt;/p&gt;&lt;p&gt;The simulated atmospheric CO&lt;sub&gt;2&lt;/sub&gt; and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; contributions are primarily of fossil origin (90%). Anthropogenic emissions contribute between 60% in February, and 20% in July/August, to the CO&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; uptake during June, July and August roughly outweighs CO&lt;sub&gt;2&lt;/sub&gt; contributions from anthropogenic activities and biosphere respiration at JFJ.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;REFERENCES&lt;/p&gt;&lt;p&gt;[1] Tuzson et al., 2011. ACP, 11, 1685&lt;/p&gt;&lt;p&gt;[2] R&amp;#246;ckmann et al., 2016. ACP, 16, 10469&lt;/p&gt;&lt;p&gt;[3] Vardag et al., 2016. Biogeosciences, 13, 4237&lt;/p&gt;&lt;p&gt;[4] Tuzson et al., 2008. Appl. Phys. B, 92, 451&lt;/p&gt;&lt;p&gt;[5] Sturm et al., 2013. AMT 6, 1659&lt;/p&gt;