Top-down constraints on N2O emissions from Canada

Canadian nitrous oxide (N2O) emissions over 2011–2015 are estimated using the CarbonTracker-Lagrange (CT-L) regional inversion. The uncertainty in the whole-country total is high, on the order of 100% or more, with a net flux not significantly different from zero. Emissions are better resolved in Canadian cropland, primarily in Alberta, Saskatchewan, and Manitoba, where the total flux is estimated at 0.08 ± 0.08 Tg N/yr. The uncertainty is improved by the addition of 4 new Canadian sites to the inversion, but remains large, mainly due to the low signal to background ratio at all Canadian N2O measurement sites. The seasonal patterns in Canadian cropland emissions suggest a dual maximum, with a late winter freeze-thaw pulse and a growing season flux of similar magnitude. Overall, Canadian cropland accounts for ∼1% of the global anthropogenic N2O source according to the inversion, although some process-based models suggest a source more on the order of 2%.