| 10 Mar 2026
Atmospheric CO2 and CH4 measurements at Schauinsland station, Germany: A comparative study of diurnal and seasonal variations at 12 and 35 m intake height
Abstract. At the atmospheric monitoring station Schauinsland (Black Forest, Germany), high-precision long-term measurements of atmospheric CO2 and CH4 have been conducted since 1972 and 1991, respectively. An additional air intake at 35 m a.g.l. (above ground level) has been installed alongside the existing intake at 12 m a.g.l in September 2021. To ensure consistency and continuity of the historic CO2 and CH4 time series, a three-year comparison between the two intake heights has been carried out. This revealed systematic differences in CO2 mole fractions between the two levels: During summer daytime diurnal mean CO2 mole fractions at 35 m are up to 0.5 ppm higher, while night-time values are up to 1.1 ppm lower, compared to 12 m, resulting in smaller diurnal amplitudes at 35 m. Seasonal mean CO2 mole fractions are lowered by up to 0.36 ppm at 35 m relative to 12 m in summer, whereas no significant differences are observed in winter. The diurnal and seasonal mean CH4 mole fraction differences between the two intake heights are negligible. However, highly frequent CH4 spikes originating from nearby grazing cows, which are present only during the summer months, increase hourly mean mole fractions at 12 m by up to 38 ppb, while no significant influence is measured at 35 m. The REBS (Robust Extraction of the Baseline Signal) algorithm is applied to the minutely CH4 summer data at 12 m and proved to be an effective approach for identification of data affected by very local influences.
General comments
This manuscript by Großmann et al. presents a comparison between the in-situ CO₂ and CH₄ time series recorded at two different sampling heights at the atmospheric monitoring station Schauinsland (Germany). Schauinsland is one of the global reference sites for greenhouse gas observations and hosts the longest CO₂ time series in Europe. To minimize the potential impact of local perturbations on the measured CO₂ and CH₄ signals, the station—previously operating with a 12 m a.g.l. sampling inlet since 2011—has recently been equipped with an additional inlet at 35 m a.g.l.
This study specifically analyzes the consistency of the CO₂ and CH₄ signals obtained from the two sampling inlets and quantifies systematic biases in the diurnal and seasonal cycles associated with using the higher inlet.
The topic is well within the scope of AMT. The paper is clearly written, the methodology is appropriate, and the results are robust and well described. Moreover, this work represents an important reference for users of the Schauinsland data series. I therefore recommend publication after the authors address the following minor points.
Specific comments
Line 90: What is the inner diameter of the inlet tube, and what is the residence time of air within it?
Section 2.5 (Data treatment): Is the residence time of air in the 70 m long tube of the 35 m inlet considered in the comparison?
Section 2.6 (Robust Extraction of Baseline Signal — REBS) spike detection algorithm: I recommend specifying here the beta and bandwidth values used in evaluating the spike detection method.
Line 181:
“However, on certain days, elevated CO₂ mole fractions are observed at the 12 m intake, occasionally reaching CO₂ enhancements of up to 2 ppm compared to the 35 m intake, most notably during the night of 1 to 2 February 2024 and again on 4 February 2024.”
Could you discuss possible causes for these enhancements that appear only in the 12 m inlet?
Figures 6, 7, 13, S1, S2: Please specify what the error bars represent.
Line 302: Based on the data distributions, it appears that even in winter the differences are skewed toward higher values, suggesting occurrences of elevated CH₄ at the 12 m inlet. What might be the cause? Is the soil snow‑covered during winter?
Line 381: Please provide the fractions of paired data that exceeded the WMO compatibility goal for both the original and the despiked datasets.
Line 411: Has a similar analysis been performed comparing the 6 m and 12 m air inlets?
Line 435: Could you provide recommendations for ensuring consistent use of the historical dataset together with the new 35 m inlet data?