Ground-based FTIR retrievals of SF 6 on Reunion Island

SF 6 total columns are successfully retrieved from FTIR measurements (Saint Denis and Maido) at Reunion Island (21° S, 55° E) between 2004–2016 using the SFIT4 algorithm: the retrieval strategy and the error budget are presented. The FTIR SF 6 retrieval has independent information in only one individual layer, covering the whole troposphere and the lower stratosphere. The trend of SF 6 is analysed based on the FTIR retrieved dry air column-averaged mole fractions ( X SF 6 ) at Reunion Island, the in-situ measurements at America Samoa (SMO) and the collocated satellite measurements (MIPAS and ACE-FTS) in the southern tropics. The SF 6 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 SF 6 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.