European source and sink areas of CO₂ retrieved from Lagrangian transport model interpretation of combined O₂ and CO₂ measurements at the high alpine research station Jungfraujoch

Abstract. The University of Bern monitors carbon dioxide (CO₂) and oxygen (O₂) at the High Altitude Research Station Jungfraujoch since the year 2000 by means of flasks sampling and since 2005 using a continuous in situ measurement system. This study investigates the transport of CO₂ and O₂ towards Jungfraujoch using backward Lagrangian Particle Dispersion Model (LPDM) simulations and utilizes CO₂ and O₂ signatures to classify air masses. By investigating the simulated transport patterns associated with distinct CO₂ concentrations it is possible to decipher different source and sink areas over Europe. The highest CO₂ concentrations, for example, were observed in winter during pollution episodes when air was transported from Northeastern Europe towards the Alps, or during south Foehn events with rapid uplift of polluted air from Northern Italy, as demonstrated in two case studies.

To study the importance of air-sea exchange for variations in O₂ concentrations at Jungfraujoch the correlation between CO₂ and APO (Atmospheric Potential Oxygen) deviations from a seasonally varying background was analyzed. Anomalously high APO concentrations were clearly associated with air masses originating from the Atlantic Ocean, whereas low APO concentrations were found in air masses advected either from the east from the Eurasian continent in summer, or from the Eastern Mediterranean in winter. Those air masses with low APO in summer were also strongly depleted in CO₂ suggesting a combination of CO₂ uptake by vegetation and O₂ uptake by dry summer soils. Other subsets of points in the APO-CO₂ scatter plot investigated with respect to air mass origin included CO₂ and APO background values and points with regular APO but anomalous CO₂ concentrations. Background values were associated with free tropospheric air masses with little contact with the boundary layer during the last few days, while high or low CO₂ concentrations reflect the various levels of influence of anthropogenic emissions and the biosphere. The pronounced cycles of CO₂ and O₂ exchanges with the biosphere and the ocean cause clusters of points and lead to a seasonal pattern.