Long-term time series of ground-based NDACC FTIR trace gases at Paris between 2011 and 2022

Abstract. We present long‐term atmospheric trace gas measurements at Paris (48°50′04″ N, 2°21′02″ E; 60 m a.s.l.), using ground-based remote sensing technique and covering the period 2011–2022. The Fourier Transform Spectrometer of the Paris station (FTS-Paris) has been operated regularly since 2011 and has been part of the Total Carbon Column Observing Network (TCCON) since 2014. It also recently joined the Network for the Detection of Atmospheric Composition Change – InfRared Working Group (NDACC-IRWG). Here we describe the instrument setup, the automated operation mode, and the SFIT4 retrieval strategy for ten Paris NDACC-IRWG products: CH4, N2O, CO, C2H6, H2CO, NO2, OCS, HCl, HF and HCN. The nominal retrieval settings were selected by comparing and evaluating the OEM and TP methods, using spectral fit quality, vertical profiles, degrees of freedom, averaging kernels, and retrieval errors as criteria. Data quality is assessed through error characterization, instrument line shape sensitivity study, comparison with previous PROFFIT9 retrievals, and evaluation of the post-processing filtering criteria. Retrieval noise dominates the random error, while spectroscopic uncertainties are the main source of the systematic error. Post-processing filtering removes about 2–6 % of data, mostly outliers. The 2011–2022 time series show increasing trends for CH4 and N2O, decreasing trends for CO, C2H6, H2CO, NO2 and OCS, and an undefined long-term evolution for HCl. HF and HCN records only cover the 2018–2022 period and derived trends require caution. The Paris FTIR measurements have been archived in the NDACC data repository and on Zenodo using the Hierarchical Data Format version 4 (HDF4).