Top-down constraints on N2O emissions from Canada.

Canadian nitrous oxide (N 2 O) 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 N 2 O 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 N 2 O source according to the inversion, although some process-based models suggest a source more on the order of 2%. • Canadian cropland emits 0.08 ± 0.08 Tg N 2 O–N/yr according to a regional inversion. • This represents ∼1% of the global anthropogenic N 2 O source. • Including 4 new Canadian monitoring sites modestly improves inversion uncertainty. • Canadian cropland N 2 O fluxes have comparable freeze-thaw and growing season peaks. [ABSTRACT FROM AUTHOR]