S1 Additional validation of Arctic stratospheric ozone from the CAMS reanalysis.

Figure S1 shows a comparison between the CAMS reanalysis and Fourier-Transform Infrared Spectroscopy (FTIR) observations from the Network for the Detection of Atmospheric Composition Change (NDACC) network. A detailed description of the instruments and the applied methodologies for all NDACC FTIR observations can be found in Langerock et al. (2015). FTIR measurement techniques are sensitive to the stratosphere and have a typical uncertainty of 5% for the total column. Figure S1 illustrates that the CAMS reanalysis TCO3 values show a slight underestimation against NDACC FTIR data, which is below 10% for most stations and falls within the measurement uncertainty of 5% for a large part of the timeseries.