AbstractRegional emissions of methane and their attribution to a variety of sources presently have large uncertainties. Measurements of radiocarbon (14C) in methane (CH4) may provide a method for identifying regional CH4 emissions from fossil versus biogenic sources because adding 14C‐free fossil carbon reduces the 14C/C ratio (Δ14CH4) in atmospheric CH4 much more than biogenic carbon does. We describe an approach for estimating fossil and biogenic CH4 at regional scales using atmospheric Δ14CH4 observations. As a case study to demonstrate expected Δ14CH4 and Δ14CH4‐CH4 relationships, we simulate and compare Δ14CH4 at a network of sites in California using two gridded CH4 emissions estimates (Emissions Database for Global Atmospheric Research, EDGAR, and Gridded Environmental Protection Agency, GEPA) and the CarbonTracker‐Lagrange model for 2014, and for 2030 under business‐as‐usual and mitigation scenarios. The fossil fraction of CH4 (F) is closely linked with the simulated Δ14CH4‐CH4 slope and differences of 2–21% in median F are found for EDGAR versus GEPA in 2014, and 7–10% for business‐as‐usual and mitigation scenarios in 2030. Differences of 10% in F for >200 ppb of added CH4 produce differences of >10‰ in Δ14CH4, which are likely detectable from regular observations. Nuclear power plant 14CH4 emissions generally have small simulated median influences on Δ14CH4 (0–7‰), but under certain atmospheric conditions they can be much stronger (>30‰) suggesting they must be considered in applications of Δ14CH4 in California. This study suggests that atmospheric Δ14CH4 measurements could provide powerful constraints on regional CH4 emissions, complementary to other monitoring techniques.

中文翻译：

---

使用大气放射性碳在区域范围内检测化石和生物甲烷

摘要目前，区域甲烷排放及其各种来源的归属具有很大的不确定性。放射性碳的测量（14C) 甲烷 (CH4）可以提供一种识别区域CH的方法4化石源排放与生物源排放相比，因为添加14无碳化石碳减少了14C/C 比 (Δ14CH4) 大气中 CH4比生物碳多得多。我们描述了一种估算化石和生物 CH 的方法4在区域尺度上使用大气 Δ14CH4观察。作为证明预期 Δ 的案例研究14CH4和 Δ14CH4‐CH4关系，我们模拟并比较 Δ14CH4在加利福尼亚州的一个站点网络中，使用两个网格 CH4照常和缓解情景下的 2014 年和 2030 年排放估算（全球大气研究排放数据库，EDGAR 和网格环境保护局，GEPA）和 CarbonTracker-Lagrange 模型。CH 的化石部分4(F) 与模拟的 Δ 密切相关14CH4‐CH42014 年 EDGAR 与 GEPA 的斜率和 F 中位数差异为 2-21%，2030 年一切照旧和缓解方案的 F 中位数差异为 7-10%。添加 CH >200 ppb 时，F 差异为 10%4Δ 产生 >10‰ 的差异14CH4，这可能可以从常规观察中检测到。核电站14CH4排放量通常对 Δ 的模拟中值影响较小14CH4(0–7‰)，但在某些大气条件下，它们可能更强 (>30‰)，这表明在 Δ 的应用中必须考虑它们14CH4在加利福尼亚。这项研究表明大气 Δ14CH4测量可以对区域 CH 提供强有力的约束4排放，对其他监测技术的补充。