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Abstract:
This study examines N2O emission estimates from 5 different atmospheric inversion frameworks. The 5 frameworks differ in the choice of atmospheric transport model,
meteorological data, prior uncertainties and inversion method but use the same prior
5 emissions and observation dataset. The mean emissions for 2006 to 2008 are compared
in terms of the spatial distribution and seasonality. Overall, there is a good agreement
among the inversions for the mean global total emission, which ranges from 16.1
to 18.7 TgNyr−1 and is consistent with previous estimates. Ocean emissions represent
between 31% and 38% of the global total compared to widely varying previous esti10
mates of 24% to 38%. Emissions from the northern mid to high latitudes are likely to
be more important, with a consistent shift in emissions from the tropics and subtropics
to the mid to high latitudes in the Northern Hemisphere; the emission ratio for 0–30 N
to 30–90 N ranges from 1.5 to 1.9 compared with 2.9 to 3.0 in previous estimates. The
largest discrepancies across inversions are seen for the regions of South and East
15 Asia and for tropical and South America owing to the poor observational constraint for
these areas and to considerable differences in the modelled transport, especially interhemispheric
exchange rates and tropical convection. Estimates of the seasonal cycle
in N2O emissions are also sensitive to errors in modelled stratosphere-to-troposphere
transport in the tropics and southern extra-tropics. Overall, the results show a conver20 gence in the global and regional emissions compared to previous independent studies.
