An intercomparison of total column-averaged nitrous oxide between ground-based FTIR TCCON and NDACC measurements at seven sites and comparisons with the GEOS-Chem model

Nitrous oxide (N2O) 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 N2O mole fraction. In this study, the dry-air column-averaged mole fractions of N2O (X-N2O) from the TCCON and NDACC measurements are compared against each other at seven sites around the world (Ny-Alesund, Sodankyla, Bremen, Izana, Reunion, Wollongong, Lauder) in the time period of 2007-2017. The mean differences in X-N2O between TCCON and NDACC (NDACC-TCCON) at these sites are between -3.32 and 1.37 ppb (-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 N2O 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 X-N2O measurement is strongly affected by its a priori profile.