Abstract. Correlations of night-time atmospheric methane (CH₄) and ²²²Radon (²²²Rn) observations in Heidelberg, Germany, were evaluated with the Radon Tracer Method (RTM) to estimate the trend of annual CH₄ emissions from 1996–2020 in the catchment area of the station. After an initial 30 % decrease of emissions from 1996 to 2004, no further systematic trend but small inter-annual variations were observed thereafter. This is in accordance with the trend of emissions until 2010 reported by the EDGARv6.0 inventory for the surroundings of Heidelberg. We show that the reliability of total CH₄ emission estimates with the RTM critically depends on the accuracy and representativeness of the ²²²Rn exhalation rate from soils in the catchment area of the site. Simply using ²²²Rn fluxes as estimated by Karstens et al. (2015) could lead to biases in the estimated greenhouse gases (GHG) fluxes as large as a factor of two. RTM-based GHG flux estimates also depend on the parameters chosen for the night-time correlations of CH₄ and ²²²Rn, such as the night-time period for regressions as well as the R² cut-off value for the goodness of the fit. Quantitative comparison of total RTM-based top-down with bottom-up emission inventories requires representative high-resolution footprint modelling, particularly in polluted areas where CH₄ emissions show large heterogeneity. Even then, RTM-based estimates are likely biased low if point sources play a significant role in the station/observation footprint as their emissions are not captured by the RTM method. Long-term representative ²²²Rn flux observations in the catchment area of a station are indispensable in order to apply the RTM method for reliable quantitative flux estimations of GHG emissions from atmospheric observations.

中文翻译：

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使用氡示踪法 (RTM) 估算区域温室气体 (GHG) 排放量的局限性——海德堡甲烷案例研究

摘要。使用氡示踪法 (RTM) 评估了德国海德堡夜间大气甲烷 (CH ₄ ) 和²²²氡 ( ²²² Rn) 观测值的相关性，以估计集水区 1996-2020年年度 CH ₄排放量的趋势车站区域。从 1996 年到 2004 年，排放量最初减少了 30%，此后没有进一步的系统趋势，但观察到年际变化很小。这与 EDGARv6.0 清单报告的海德堡周边地区截至 2010 年的排放趋势一致。我们表明，使用 RTM 估计总 CH ₄排放量的可靠性在很大程度上取决于场地集水区土壤的²²² Rn 呼出率。简单地使用Karstens 等人估计的²²² Rn 通量。(2015) 可能导致估计的温室气体 (GHG) 流量偏差高达两倍。基于 RTM 的 GHG 通量估计还取决于为 CH ₄和²²² Rn的夜间相关性选择的参数，例如回归的夜间时段以及拟合优度的 R ²截止值. 基于 RTM 的自上而下总排放清单与自下而上排放清单的定量比较需要具有代表性的高分辨率足迹建模，特别是在 CH _{4 的}污染区域排放表现出很大的异质性。即便如此，如果点源在台站/观测足迹中发挥重要作用，则基于 RTM 的估计可能偏低，因为它们的排放未被 RTM 方法捕获。为了应用 RTM 方法对来自大气观测的温室气体排放量进行可靠的定量通量估算，站点集水区的长期代表性²²² Rn 通量观测是必不可少的。