30 years of total column ozone and aerosol optical depth measurements using the Brewer spectrophotometer in Poprad-Gánovce, Slovakia

Abstract. Long-term observations (1993–2024) of total column ozone (TCO) and aerosol optical depth at 320 nm (AOD320) from the Brewer spectrophotometer at Poprad-Gánovce, Slovakia, were analysed. The data used in this study are closely tied to three environmental issues driven by human activities: ozone depletion, climate change, and air pollution caused by aerosols. Both parameters exhibit distinct seasonal variability, with AOD320 peaks in April and August and TCO maxima from February to April. AOD320 shows a statistically significant long-term decrease (−0.057 ± 0.005 per decade), reflecting reduced anthropogenic emissions. The lowest annual mean occurred in 2020, corresponding to the first year of the COVID-19 pandemic. In contrast, TCO shows no clear trend (0.0 ± 0.4 DU per decade), whereas the tropopause height increases markedly (105 ± 7 m per decade) and exerts an inverse influence on TCO. After removing this effect, a positive TCO trend (1.3 ± 0.3 DU per decade) appears, while the tropopause-related component decreases (−1.3 ± 0.1 DU per decade). The most significant positive linear trend in tropopause height was identified in August (200 ± 70 m per decade), while the strongest negative TCO trend also occurred in August (−3.6 ± 1.8 DU per decade). Only about one third of this August TCO decrease is explained by the tropopause rise. LOTUS regression confirmed the inverse TCO-tropopause relationship and revealed significant ENSO (positive) and QBOB (negative) influences. A weak positive trend in TCO since 1997 (2.0 ± 1.2 DU) indicates ongoing recovery from ODS reductions.