Nitrous oxide (inline-formulaN2O) is an important greenhouse gas and it can also generate nitric oxide, which depletes ozone in the stratosphere. It is a common target species of ground-based Fourier transform infrared (FTIR) near-infrared (TCCON) and mid-infrared (NDACC) measurements. Both TCCON and NDACC networks provide a long-term global distribution of atmospheric inline-formulaN2O mole fraction. In this study, the dry-air column-averaged mole fractions of inline-formulaN2O (inline-formula
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) from the TCCON and NDACC measurements are compared against each other at seven sites around the world (Ny-Ålesund, Sodankylä, Bremen, Izaña, Réunion, Wollongong, Lauder) in the time period of 2007–2017. The mean differences in inline-formula
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between TCCON and NDACC (NDACC–TCCON) at these sites are between inline-formula−3.32 and 1.37 ppb (inline-formula−1.1 %–0.5 %) with standard deviations between 1.69 and 5.01 ppb (0.5 %–1.6 %), which are within the uncertainties of the two datasets. The NDACC inline-formulaN2O retrieval has good sensitivity throughout the troposphere and stratosphere, while the TCCON retrieval underestimates a deviation from the a priori in the troposphere and overestimates it in the stratosphere. As a result, the TCCON inline-formula
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measurement is strongly affected by its a priori profile.
page1394Trends and seasonal cycles of inline-formula
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are derived from the TCCON and NDACC measurements and the nearby surface flask sample measurements and compared with the results from GEOS-Chem model a priori and a posteriori simulations. The trends and seasonal cycles from FTIR measurement at Ny-Ålesund and Sodankylä are strongly affected by the polar winter and the polar vortex. The a posteriori inline-formulaN2O fluxes in the model are optimized based on surface inline-formulaN2O measurements with a 4D-Var inversion method. The inline-formula
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trends from the GEOS-Chem a posteriori simulation (inline-formula0.97±0.02 (inline-formula1σ) ppb yrinline-formula−1) are close to those from the NDACC (0inline-formula.93±0.04 ppb yrinline-formula−1) and the surface flask sample measurements (inline-formula0.93±0.02 ppb yrinline-formula−1). The inline-formula
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trend from the TCCON measurements is slightly lower (inline-formula0.81±0.04 ppb yrinline-formula−1) due to the underestimation of the trend in TCCON a priori simulation. The inline-formula
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trends from the GEOS-Chem a priori simulation are about 1.25 ppb yrinline-formula−1, and our study confirms that the inline-formulaN2O fluxes from the a priori inventories are overestimated. The seasonal cycles of inline-formula
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from the FTIR measurements and the model simulations are close to each other in the Northern Hemisphere with a maximum in August–October and a minimum in February–April. However, in the Southern Hemisphere, the modeled inline-formula
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values show a minimum in February–April while the FTIR inline-formula
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retrievals show different patterns. By comparing the partial column-averaged inline-formulaN2O from the model and NDACC for three vertical ranges (surface–8, 8–17, 17–50 km), we find that the discrepancy in the inline-formula
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seasonal cycle between the model simulations and the FTIR measurements in the Southern Hemisphere is mainly due to their stratospheric differences.