Temporal variation of atmospheric fossil and modern CO₂ Excess at a central european rural tower station between 2008 and 2014

In 2008, the atmospheric CO₂ measurements at the Hegyhátsál rural tower station were extended further by ¹⁴CO2 air sampling from two elevations (115 and 10 m a.g.l.), in cooperation with HEKAL (ICER). Since then, a complete six-year-long (2008-2014) dataset of atmospheric CO2, Δ¹⁴C, fossil, and modern CO₂ excess (relative to Jungfraujoch) has been assembled and evaluated. Based on our results, the annual mean CO₂ mole fraction rose at both elevations in this period. The annual mean Δ¹⁴CO2 values decreased with a similar average annual decline. Based on our comparison, planetary boundary layer height obtained by modeling has a larger influence on the variation of mole fraction of CO₂ (relative to Jungfraujoch), than on its carbon isotopic composition, i.e. the boundary layer rather represents a physical constraint. Fossil fuel CO₂ excess at both elevations can rather be observed in wintertime and mainly due to the increased anthropogenic emission of nearby cities in the region. The mean modern CO₂ excess at both elevations was even larger in winter, but it drastically decreased at 115 m by summer, while it remained at the winter level at 10 m.