Regional sources of nitrous oxide over the United States: Seasonal variation and spatial distribution

This paper presents top‐down constraints on the magnitude, spatial distribution, and seasonality of nitrous oxide (N₂O) emissions over the central United States. We analyze data from tall towers in 2004 and 2008 using a high resolution Lagrangian particle dispersion model paired with both geostatistical and Bayesian inversions. Our results indicate peak N₂O emissions in June with a strong seasonal cycle. The spatial distribution of sources closely mirrors data on fertilizer application with particularly large N₂O sources over the US Cornbelt. Existing inventories for N₂O predict emissions that differ substantially from the inverse model results in both seasonal cycle and magnitude. We estimate a total annual N₂O budget over the central US of 0.9–1.2 TgN/yr and an extrapolated budget for the entire US and Canada of 2.1–2.6 TgN/yr. By this estimate, the US and Canada account for 12–15% of the total global N₂O source or 32–39% of the global anthropogenic source as reported by the Intergovernmental Panel on Climate Change in 2007.