The authors discuss the trends, budget and deposition of TFA in Switzerland. The study is very comprehensive, including measurements of TFA in rainwater, rivers, lakes, modelling of the deposition of TFA from fluorinated gases, and estimated of TFA from pharmaceuticals and plant protection products. The paper has a good and extensive introduction of TFA. The methods, measurements and model calculations are described in great detail. The results are also described in detail with all their uncertainties and caveats. I want to compliment the authors with this paper, well done. I only have some smaller textual comments.

Some specifics comments on the text:

L9: Specify the region the deposition of 24.5 Mg applies to.

L11-12: “In croplands … deposition”. I suggest removing this sentence. Although interesting, it disrupts the flow of the abstract and is does not add relevant information for the remainder of the abstract.

L12: It is not clear how old the “archived samples” are. Are they from the 1990s?

L17: You write about the risk assessment, but later in the paper you mention that there is no consensus of the risks of TFA (L81). I suggest you rephrase the sentence, e.g. “for refining the assessment of TFA sources for potential health and environmental risks.”.

L53-58: This a very long sentence and therefore hard to read. Please rephrase.

L474: Data from WWTP could indeed be valuable, but are they a new source not accounted for yet? Do the WWTPs not discharge their water on the rivers?

L657: “The gap in explained deposition…”. Where the gap refers to is not clear from the previous sentences. Please add some text here.

P30, table 2: There is a typo in the compound name: It should be HFC-43-10mee, not HFC-41-10mee

The authors present a comprehensive assessment of TFA concentrations recorded in precipitation and surface waters in Switzerland 2021-2023. They compare these measurements with those taken from archived water samples and demonstrate significant increases in TFA concentrations in recent years. They also conduct a number of modelling studies to determine TFA deposition from the atmosphere and determine that this cannot be the sole driver of the observed TFA increases. They propose terrestrial inputs from PPP and veterinary pharmaceuticals as a more significant contributor to TFA contamination in surface waters. They also suggest an atmospheric TFA source that predates the introduction of known precursors (though it seems they are suggesting a further anthropogenic source, in which case this should be made clearer in the abstract).

The report is generally well written and presents an important study into TFA contamination at a national level. However, there a few areas that need further discussion or that have been omitted. Firstly, there should be full justification of the veracity of the archived water samples as these form a major basis for many of the conclusions drawn. Secondly, the relationship between CF₃CHO and TFA formation has been omitted from this study. Given the recent literature on the potential impacts of CF₃CHO on TFA concentrations and the uncertainty it introduces to TFA yields etc. it should at least be discussed and could go some way to closing the gap seen between the modelled deposition and the measurements.

More generally, tables and figures could be better placed throughout the manuscript (i.e. near the text the references them) and more accessible for those with colour-blindness (though I appreciate this is difficult to achieve with figures such as those presented here).

Specific comments:

Line 7: unnecessary ‘-‘

Line 8: Where does the 60-70% come from? From the other % range seems like it should be 52-71%?

Line 11: Presumably this value refers to total atmospheric deposition (wet + dry?)

Line 14: 1990s instead of 1990ies (also occurs …)

Line 24: There are some reports that suggest TFA may bioaccumulate in plant material

Line 39: ‘As a consequence’ as opposed to ‘In consequence’, ‘potential risk’ as opposed to ‘risk’

Line 56: () within ()

Line 117: Is the conducted test sufficient to prove the veracity of the archived samples?

Line 169: Error of 10% for the emissions estimates – please justify this number?

Line 197: You should justify why the model was run for 60 days, as from a trajectory viewpoint it seems far too long to give a reliable distribution

Line 241: What is the timescale of hydrolysis of TFF to TFA? 

Line 247: Why did you use The Henry’s Law constant of HNO₃ when there are reported values for TFA? There is uncertainty in the TFA value that may mean it diverges from the HNO₃ value. Given the importance of this parameter in wet deposition and the importance of this loss to the atmospheric fate of TFA, the uncertainty of this would be a useful thing to explore. Regardless, the value used should be given in the text with ref

Line 255-275: There should be mention of recent publications relating to CF₃CHO that dispute TFA yields, specifically the 4-60% value for HFO-1336mzzZ, and introduce extra uncertainty that hasn’t been accounted for in this study as it stands

Line 274: Typo ‘emissions’

Line 280: Are the samples below the estimated quantification limit considered in the average? How can you quantify a value below the limit of quantification? What is the limit of detection? How is the limit of quantification derived?

Line 281: Is this 0.58 ± 0.58 correct?

Line 283-303: Are you using T-dependent rate constants for HFO+OH? Some of the HFOs you are considering have a negative relationship between k and T

Line 311: Could deposition not also be a driver of load seasonality (in addition to discharge seasonality)?

Line 327-329: ‘underlines’ and ‘underlining’ should be replaced with ‘supports’ and ‘reinforcing’

Line 330-334: Does this evidence not serve as an argument against pre known-precursor TFA?

Line 343: ‘No significant TFA gradients with depths were detected in the other lakes’ so concentrations at depth were the same as the surface? Were the values elevated?

Line 383: Replace ‘the latter’ with ‘this’

Line 391: ‘large HFO emissions in the Po Valley’ ? Are these emissions simulated in the model at an appropriate resolution to be able to make this claim?

Line 400: ‘compared with’ instead of ‘compared to’

Line 409: Remove ‘as well’ and replace with also earlier in the sentence

Line 415: It also suggests that if these unknown sources exist, they are likely to be anthropogenic

Line 426: What is the estimated combined uncertainty of the simulated TFA deposition? It should be reported here along with the specific contributions of the TFA yield vs the precursor emissions

Line 430-431: This sentence ‘faster (slower) … increased (decrease)’ is not worded clearly.

Line 448: ‘which is in the range smaller 0.3%’ does not make sense and there is also an unclosed ‘(‘

Line 451: ‘For non-atmospheric sources of TFA’

Line 484: Need an ‘is’ between ‘discharge’ and ‘below’

Line 489: This should be more specific e.g. ‘PPPs may be a more relevant source of TFA to environmental aqueous phases (i.e rivers and lakes) in Switzerland’

Line 494: Remove () from reported flux to be consistent

Line 503: Missing ‘(‘

Line 511: TFA in rainwater in Bayreuth?

Line 514-518: Clarify that you’re talking about TFA concentration in rainwater and in archived plant material

Line 528: Was 2019 when HFO use started to increase exponentially? If yes, I would explicitly make this link

Line 542: You should be specific as to what other sources you are suggesting (agricultural run-off? Natural sources?)

Line 548: Do these processes release fluorocarbons into the environment via wastewater etc only or is there a potential gaseous emission?

Line 627: Also there’s massive uncertainty in the yields?

Figure 2 & 3: Additional x-ticks representing the months or every 3 months would make these figures easier to interpret where variations are not exactly halfway through the year

Table 2 & 3: Should present the 3 yields used rather than the range, lifetime of ‘1’ should be reported as ‘1.0’ for consistency, last column in each needs () around units