Ground-based FTIR retrievals of SF₆ on Reunion Island

SF₆ total columns were successfully retrieved from FTIR (Fourier transform infrared) measurements (Saint Denis and Maïdo) on Reunion Island (21° S, 55° E) between 2004 and 2016 using the SFIT4 algorithm: the retrieval strategy and the error budget were presented. The FTIR SF₆ retrieval has independent information in only one individual layer, covering the whole of the troposphere and the lower stratosphere. The trend in SF₆ was analysed based on the FTIR-retrieved dry-air column-averaged mole fractions (<i>X</i>_SF₆) on Reunion Island, the in situ measurements at America Samoa (SMO) and the collocated satellite measurements (Michelson Interferometer for Passive Atmospheric Sounding, MIPAS, and Atmospheric Chemistry Experiment Fourier Transform Spectrometer, ACE-FTS) in the southern tropics. The SF₆ annual growth rate from FTIR retrievals is 0.265 ± 0.013 pptv year⁻¹ for 2004–2016, which is slightly weaker than that from the SMO in situ measurements (0.285 ± 0.002 pptv year⁻¹) for the same time period. The SF₆ trend in the troposphere from MIPAS and ACE-FTS observations is also close to the ones from the FTIR retrievals and the SMO in situ measurements