Total ozone observations in Reykjavík, Iceland, using a Brewer spectrophotometer

The monitoring of total ozone and solar ultraviolet (UV) radiation in Reykjavík, Iceland, has been performed using an automated Brewer spectrophotometer (B199) since August 2021. A manual Dobson spectrophotometer (D050) has been in operation since the 1950s. The aim of the study was to compare the measurements of the two instruments and to assess the variability of total column ozone (TCO) in 2021–2024. The mean absolute and relative difference in the TCO measurements, defined as TCODOB – TCOBRE, was −1.1 Dobson Units (DU, −0.35 %). After applying a correction for the effective temperature of the ozone layer, the difference decreased to −0.8 DU (−0.26 %). The differences exhibited an annual cycle: in autumn and spring, the Dobson spectrophotometer underestimated total ozone, while in February and in summer, a slight overestimation was observed. February discrepancies were likely related to a frequent use of the Global Irradiance (GI) measurement mode in the Brewer spectrophotometer, which was associated with the largest positive differences between the two instruments. A statistically significant correlation was also found between relative differences, sulphur dioxide concentrations and atmospheric optical mass. During the study period, total ozone followed a standard annual course with maxima in spring and minima in autumn.