General comments

This study introduces a hybrid approach to investigating changes in stratospheric transport times, combining observational, model and reanalysis data. By incorporating observational data, the authors effectively reduce the dependency of the derived age of air trends on the input reanalysis datasets. The manuscript makes a valuable contribution to our understanding of recent changes in the Brewer-Dobson Circulation and hemispheric asymmetries, both of which are important topics of ongoing discussion within the stratospheric community.

I find the manuscript to be very well-structured and comprehensively written. While the overall quality is high, I also fully support the Major Comments (MC1 and MC2) raised by S. Chabrillat in RC1. In addition, I have a few additional minor comments, listed below. Once these have been addressed, I strongly recommend publication.

Regarding Major comments from RC1

Regarding MC1 form RC1: I agree that describing the derivation of the slopes is an important part of the manuscript, that should be addressed more clearly in a way to facilitate reader understanding and potentially reproducing the results. However, if the authors consider the details of this methodology to be well-established and not central to reproducing their results, they could provide a more detailed description in the supplementary material.

Regarding MC2 from RC2: I agree that this manuscript could benefit from highlighting the differences between prior model-based results and this hybrid approach, especially by drawing a more explicit comparison with the previous study from Ploeger and Garny (2022).

Specific comments

SC1: Line 108,109: From my understanding, only the trend in AoA interhemispheric difference is calculated from all three species mentioned, whereas the latitudinally resolved AoA trend is derived only from N₂O. A more general phrasing such as “We derive trends in both the AoA interhemispheric difference (SH-NH) and the latitudinally resolved AoA from trace gas-AoA correlations.”, may suffice, as the specific substances and their roles are specified further down.

SC2: Figure 1 caption: Please consider aligning the figure caption more closely with the information provided in the main text to enhance clarity and make it more self-descriptive. In particular, adopting the term “monthly zonal mean”, as used in the main text, would make the figure caption more accurate.

SC3: Figure 1: In the main text the magnitude of differences across the reanalyses is discussed (l. 134 – 139). To complement this discussion, you may consider adding a figure showing a box plot time series (one box plot per year, each box based on 5 values (reanalyses and observations annual mean)), which might help highlight periods of low or high agreement between different reanalyses and observations.

SC4: Figure 2 caption: I suggest further elaborating on the figure caption to make it more self-descriptive. In particular, the caption should state that the correlation between AoA and the three trace gases is shown and that atmospheric pressure is used to draw vertical profiles.

SC5: Figure 3 caption: Again I think that you should add information for clarity. E.g. you could use “top row”, “middle row” and “bottom row” to avoid ambiguities. Also you could add “at different pressure levels” or something similar to the first sentence of the caption.

SC6: Figure 4 shows that the AoA anomalies are consistent across different input reanalyses. The manuscript could benefit from a clearer discussion of how similar the results are across reanalyses, ideally with metrics to quantify this agreement (such as correlation coefficients).

Technical suggestions

• 225: “some unaccounted sources […]” without the "for" for better readability
• You might consider uploading your code used to derive your results, ideally in the form of a Jupyter notebook, to enhance reproducibility and future application.