Comment on egusphere-2026-265

<strong class="journal-contentHeaderColor">Abstract.</strong> Radiocarbon (¹⁴C) is a valuable tracer to determine the relative fossil fractions of emitted carbonaceous greenhouse gases, such as CO₂ and CH₄. While atmospheric ∆¹⁴CO₂ measurements have been conducted at multiple sites for several decades, ∆¹⁴CH₄ measurements remain more limited, mainly due to measurement challenges. In addition, nuclear power plant ¹⁴CH₄ emissions can complicate data interpretation. In this study, biweekly ∆¹⁴CH₄ and ∆¹⁴CO₂measurements at the Swiss High-Altitude Research Station Jungfraujoch (JFJ, about 3500&nbsp;m&nbsp;a.s.l.) between 2019 and 2024 are presented. Over this period, ∆¹⁴CH₄ values showed an increase from 350&nbsp;&plusmn;&nbsp;19&nbsp;&permil; to 381&nbsp;&plusmn;&nbsp;13&nbsp;&permil;, while ∆¹⁴CO₂ values decreased from -2.0&nbsp;&plusmn;&nbsp;3.8&nbsp;&permil; to -12.7&nbsp;&plusmn;&nbsp;2.0&nbsp;&permil;, respectively.&nbsp;The former is related to the slight increase of ¹⁴CH₄ emissions from the nuclear industry over the last years, while the latter is linked to the dilution of the ¹⁴CO₂ signal due to the release of ¹⁴C-devoid CO₂ from combustion of fossil fuels. Despite its high elevation, JFJ is still influenced by nuclear power plants (NPPs) operating in Europe. Considering a European-scale atmospheric dispersion model and ¹⁴CH₄ and ¹⁴CO₂ emissions from European NPPs, the mean nuclear ¹⁴C contribution to our individual measurements was estimated to be 7&nbsp;&plusmn;&nbsp;9&nbsp;&permil; for ∆¹⁴CH₄ and 0.2&nbsp;&plusmn;&nbsp;0.4&nbsp;&permil; for ∆¹⁴CO₂. Furthermore, our ∆¹⁴CH₄ measurements reasonably agree with simulated atmospheric values of ∆¹⁴CH₄ estimated by a global atmospheric one-box model and an estimation of global nuclear ¹⁴CH₄ emissions.