the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Jun 2025
30 years of total column ozone and aerosol optical depth measurements using the Brewer spectrophotometer in Poprad-Gánovce, Slovakia
Abstract. Long-term measurement series are a rare but valuable source of information. The first measurements using the Brewer ozone spectrophotometer in Slovakia began at the Poprad-Gánovce station in August 1993. As a result, a 30-year series of measurements was completed in 2023. The primary goal of this study is to present the calculated values of total column ozone (TCO) and aerosol optical depth (AOD) derived from measurements conducted with the same Brewer spectrophotometer. Additionally, this time series of measurements is enriched with tropopause height values, made possible by aerological sounding measurements regularly conducted at the Poprad-Gánovce station. This work provides a climatological and long-term trend analysis of the time series for these three atmospheric characteristics. 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. No clear trend was observed for the annual TCO averages, while AOD at 320 nm exhibited a distinct decresing trend with a slope of −0.06 per decade. The lowest annual average of AOD at 320 nm was measured in 2020, corresponding to the first year of the COVID-19 pandemic. The highest increases in tropopause height were found in August, at 200 m per decade, and in September, at 210 m per decade. The largest declines in TCO occurred in the same months, with a rate of change of −3.5 DU per decade in August and −2.8 DU per decade in September.
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- RC1: 'Good 30 years time series. Expand on tropopause height and total column ozone.', Anonymous Referee #1, 11 Jul 2025
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RC2: 'Comment on egusphere-2025-2887', Anonymous Referee #2, 11 Aug 2025
General Comments:
This study presents a valuable long-term dataset of total ozone and aerosol optical depth (AOD) derived from Brewer spectrophotometer observations. The extended temporal coverage makes the work particularly relevant. Its scientific impact would be significantly enhanced if the dataset were made publicly available through established repositories such as the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) and/or EUBREWNET, and ideally registered with a DOI to ensure long-term accessibility and citation.
The AOD retrieval methodology, originally described by Hrabcak (1998), is extensively detailed in the manuscript. I recommend condensing this section and referring to the original publication, focusing instead on the specific updates or modifications introduced in the current study.
In contrast, the description of the total ozone retrieval process is relatively brief. It would be beneficial to expand this section to include details on the o3brewer software setup, including the application of the Standard Lamp correction. Calibration procedures, and how major repairs or maintenance events were handled is also valuable. Clarifying how calibration changes were applied retrospectively and outlining the traceability of Brewer #97 to the reference triad would improve the technical transparency of the study. Additionally, how does the IOS traveling standard compare with the reference triad over the 30-year period? This comparison is essential for assessing long-term consistency.
I suggest to include the comparison of the presented dataset with existing observations archived in WOUDC (Station 331, (https://woudc.org/data/stations/331) and EUBREWNET (https://eubrewnet.aemet.es/eubrewnet/station/view/33).Single-monochromator Brewer spectrophotometers are subject to straylight interference, which introduces systematic biases in ozone and sulfur dioxide retrievals. This effect arises from the intrusion of longer-wavelength photons during short-wavelength measurements, leading to underestimation of trace gas concentrations (Savastiouk et al., 2023; Karppinen et al., 2014; Rimmer et al., 2018). To mitigate this, the dataset was filtered to include only observations with an airmass less than 4. However, as straylight effects scale with the ozone slant column (total column ozone × airmass), filtering based solely on airmass may be insufficient.
A double-monochromator Brewer spectrophotometer, which is not affected by straylight, has been operational at the station since 2015 (EUBREWNET Station 225). Comparative analysis between the single and double Brewer time series offers a means to validate the filtering approach. Moreover, straylight correction algorithms developed within EUBREWNET (Redondas et al., 2018) and by IOS (Savastiouk et al., 2023) can be use on the single brewer. Applying these corrections and assessing their impact on long-term ozone trends using the double Brewer as a reference could substantially improve the reliability of the dataset and enhance the interpretability of observed atmospheric changes.
Concernign the analysis of the series, i reconnice the difficulty to deal with a no signifciant ozone trend, could be more appropiae to use the Multiple Linear Regresion Methods like developed in LOTUS project (GitHub - usask-arg/lotus-regression) to assest the the influence of the tropopause height.
Specific comments:
I suggest to Include on Figure 1 and 2 also the series of tropopause heights
L 97 -Homogeneus, please justify
L135 Why the SO2 measurements are not reliable, please justify
L190 how the filter attenuation are obtained
L 210 : which are the differences ?
L230 : Not clear
L425: Table 5, include the errors
L450: Include reference
References
- Savastiouk, V., Diémoz, H., & McElroy, C. T. (2023). A physically based correction for stray light in Brewer spectrophotometer data analysis. Atmospheric Measurement Techniques, 16, 4785–4806. https://doi.org/10.5194/amt-16-4785-2023
- Karppinen, T., Redondas, A., García, R. D., Lakkala, K., McElroy, C. T., & Kyrö, E. (2014). Compensating for the Effects of Stray Light in Single-Monochromator Brewer Spectrophotometer Ozone Retrieval. Atmosphere-Ocean, 53(1), 66–73. https://doi.org/10.1080/07055900.2013.871499
- Rimmer, J. S., Redondas, A., & Karppinen, T. (2018). EuBrewNet – A European Brewer network (COST Action ES1207), an overview. Atmospheric Chemistry and Physics, 18, 10347–10353. https://amt.copernicus.org/preprints/amt-2018-157/amt-2018-157-RC1.pdf
Citation: https://doi.org/10.5194/egusphere-2025-2887-RC2
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- 1
The manuscript presents 30 years of total column ozone and aerosol optical depth data measured by a Brewer Spectrometer at the Poprad Ganovce station in Slovakia, in Eastern Europe. In addition, tropopause height data are presented from regular radiosonde lauches at the same site. In large parts, the paper is an update of a previous paper by Hrabčák et al. (2018), which uses the same instrument and methods. The authors report a significant decreasing trend of aerosol optical depth, in all seasons, a significant increasing trend in tropopause height, throughout most of the year, and little or no trend in total column ozone.
Consistent long-term observations, like the ones present here, are important and deserve publication in a journal like ACP. While the manuscript presents no ground-braking new results, it still confirms findings of other studies, and helps with our understanding of long-term changes in the atmosphere. I suggest publication in ACP after a few generally minor revisions.
Section 2.4, in my opinion is rather lengthy, difficult to understand, and essentially a complete repeat of what is already presented in Hrabčák et al. (2018). I suggest to remove most of section 2.4, only describe the most salient points, and otherwise refer to Hrabčák et al. (2018). Essentially, to get aerosol optical depth, you need the measured intensity S from the Brewer, the ETC S_0, and you have to subtract ozone and Rayleigh optical depths times their air-masses. Why not write the relevant Equation that provides aerosol optical depth, and then say that Hrabčák et al. (2018) explain how to get all the parameters in that Equation. If there is anything different from Hrabčák et al. (2018), then explain that. Doing this will reduce Section 2.4 from about 100 lines to 10 or 20 lines, and will make the manuscript much more readable.
Figure 2: you might want to show another panel, which would present the annual cycle of tropopause height in a similar fashion. You might be surprised how closely the annual cycle of tropopause height mirrors the annual cycle of total column ozone.
Lines 286 to 292: I would drop this paragraph. It is not needed here.
Tables 3 to 6: It would be good to have additional columns giving uncertainty estimates for the trends.
Figure 6 and Table 6: It would be very interesting to see hypothetical TCO time series and trends, in which the -11.6 DU/km "dependence" on tropopause height has been backed out. Such a hypothetical time series in Fig. 6 might show a TCO increase, and the hypothetical effect of tropopause height changes. In Table 6, the hypothetical TCO trends would mostly become more positive by around 1 DU / decade. In fact, an additional Figure showing the seasonal variation of TCO trend, tropopause height related TCO trend and "hypothetical" TCO trend would be interesting. I suggest that the authors add such a Figure and discuss it. The slightly positive "hypothetical" TCO trend would be inline with ozone increases expected to to declining ODS (possibly enhanced by stronger Brewer Dobson Circulation). The discussion would give more meaning and context for tropopause height / climate change influences on total column ozone, and would round the paper nicely.