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Quantifying nitrous oxide emissions in the U.S. Midwest - A top-down study
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  • Maximilian Eckl,
  • Anke Roiger,
  • Julian Kostinek,
  • Alina Fiehn,
  • Heidi Huntrieser,
  • Christoph Knote,
  • Zachary Barkley,
  • Stephen Ogle,
  • Bianca Baier,
  • Colm Sweeney,
  • Kenneth Davis
Maximilian Eckl
Deutsches Zentrum für Luft- und Raumfahrt (DLR)

Corresponding Author:maximilian.eckl@dlr.de

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Anke Roiger
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
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Julian Kostinek
German Aerospace Center Oberpfaffenhofen
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Alina Fiehn
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
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Heidi Huntrieser
German Aerospace Center Oberpfaffenhofen
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Christoph Knote
Ludwig-Maximilians-University (LMU)
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Zachary Barkley
The Pennsylvania State University
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Stephen Ogle
Colorado State University
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Bianca Baier
NOAA ESRL Global Monitoring Division
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Colm Sweeney
NOAA Global Monitoring Laboratory
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Kenneth Davis
The Pennsylvania State University
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Abstract

Nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance, plays a crucial role in the atmosphere. Anthropogenic emissions from agriculture contribute to a rising trend in global N2O emissions and atmospheric concentrations. However, due to insufficient direct observations, regional N2O emissions derived in bottom-up and top-down studies are highly uncertain. The U.S. Midwest is one of the most intensive agriculture areas worldwide and hence may contribute significantly to the observed trend. Recent top-down studies suggest that bottom-up estimates underestimate agricultural emissions in that area by up to an order of magnitude. Here we quantify nitrous oxide emissions in the Midwest in October 2017 and June-July 2019 with a top-down approach. Unique continuous aircraft-based measurements of N2O conducted during the ACT-America campaign together with forward WRF-Chem model simulations are used to scale the EDGAR inventory thus quantifying emissions. On average we had to upscale October 2017 and June-July 2019 agricultural EDGAR 4.3.2/5.0 emissions by a factor of 6.3/3.5 and 11.4/9.9, resulting in 0.42 nmol m-2 s-1 and 1.06 nmol m-2 s-1 emissions in the Midwest, respectively. Finally, calculations of direct soil N2O emissions from the DayCent biogeochemical model are compared to our estimates.