Ground-based FTIR retrievals of SF6 at Réunion Island

SF6 total columns are successfully retrieved from FTIR measurements (Saint Denis and Maïdo) at Réunion Island (21◦S, 55◦E) between 2004-2016 using the SFIT4 algorithm: the retrieval strategy and the error budget are presented. The FTIR SF6 retrieval has independent information in only one individual layer, covering the whole troposphere and the lower stratosphere. The trend of SF6 is analysed based on the FTIR retrieved dry air column-averaged mole fractions (XSF6 ) at Réunion Island, the in-situ measurements at America Samoa (SMO) and the collocated satellite measurements (MIPAS and 5 ACE-FTS) in the southern tropics. The SF6 annual growth rate from FTIR retrievals is 0.265±0.013 pptv/year for 2004–2016, which is slightly weaker than that from the SMO in-situ measurements (0.285±0.002 pptv/year) 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.