Evaluation of nine years of continuous δ13CO2 measurements in Heidelberg, Germany

Abstract

Measurements of atmospheric CO2 mole fraction in combination with δ13CO2 contain additional information on the CO2 source mixture at a measurement station. Instrumental developments, such as cavity ring-down spectroscopy (CRDS), have facilitated the conduction of continuous in-situ measurements of CO2 mole fraction and δ13CO2 with a high temporal resolution. This has enabled a robust and detailed local time series to be established at an urban station in Heidelberg in south-western Germany, where a CRDS G2201-i analyser has been used to measure the CO2 mole fraction and 13C/12C ratio from 2014 to 2023. This nine year time series is analysed for seasonal variations and trends in regional and local CO2 sources. We applied different approaches based on the Keeling/Miller-Tans method to identify δ13CO2 source signatures within the Heidelberg catchment area. Doing this gave δ13CO2 source values that were less depleted in the summer and more depleted in the winter, indicating a stronger biogenic effect in summer and stronger fossil fuel contributions in winter.