The densely farmed U.S. Midwest is a prominent source of nitrous oxide (N₂O) but top‐down and bottom‐up N₂O emission estimates differ significantly. We quantify Midwest N₂O emissions by combining observations from the Atmospheric Carbon and Transport‐America campaign with model simulations to scale the Emissions Database for Global Atmospheric Research (EDGAR). In October 2017, we scaled agricultural EDGAR v4.3.2 and v5.0 emissions by factors of 6.3 and 3.5, respectively, resulting in 0.42 nmol m⁻² s⁻¹ Midwest N₂O emissions. In June/July 2019, a period when extreme flooding was occurring in the Midwest, agricultural scaling factors were 11.4 (v4.3.2) and 9.9 (v5.0), resulting in 1.06 nmol m⁻² s⁻¹ Midwest emissions. Uncertainties are on the order of 50 %. Agricultural emissions estimated with the process‐based model DayCent (Daily version of the CENTURY ecosystem model) were larger than in EDGAR but still substantially smaller than our estimates. The complexity of N₂O emissions demands further studies to fully characterize Midwest emissions.

中文翻译：

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量化美国中西部地区的一氧化二氮排放量：使用高分辨率机载原位观测的自上而下的研究

美国中西部人口稠密的农田是一氧化二氮（N ₂ O）的主要来源，但自上而下和自下而上的N ₂ O排放量估算值差异很大。我们通过结合大气碳和美国运输运动的观测结果与模型模拟来量化中西部的N ₂ O排放量，以扩展全球大气研究的排放数据库（EDGAR）。2017年10月，我们将农业EDGAR v4.3.2和v5.0的排放量分别按6.3和3.5的比例进行了换算，得出0.42 nmol m ^-2  s ^-1 Midwest N ₂O排放。在中西部发生极端洪水的2019年6月/ 7月，农业比例因子为11.4（v4.3.2）和9.9（v5.0），导致1.06 nmol m ^-2  s ^-1中西部排放。不确定度约为50％。使用基于过程的模型DayCent（CENTURY生态系统模型的每日版本）估算的农业排放量大于EDGAR中的估算值，但仍大大小于我们的估算值。N ₂ O排放的复杂性需要进一步研究以充分表征中西部的排放。