Review of Reinecke et al. 2024

General comments

The manuscript proposed by Tobias Reinecke et al. entitled “Direct detection of condensed particulate polycyclic aromatic hydrocarbons on a molecular composition level at low pg m-3 mass concentrations via proton-transfer-reaction mass-spectrometry” aims at presenting the online detection of PAHs in atmospheric aerosol at very low concentrations using high resolution chemical ionization mass spectrometer. The manuscript is well constructed and very pleasant to read. The study provide sounds results from a simple field campaign conducted in Austria, showing successful detection of PAHs at environmental levels. However the paper sometimes lacks precisions, and more information should be provided to fulfil the requirement for publication in an peer reviewed international journal. I think that the paper contains valuable information that may be published after the authors improved it. My comments are listed below.

Specific Comments

Methods

It is written that ADL, IMR and inlet were modified but no details are provided. For sure it is not necessary to give all details, but a few words should be said to one can understand what has been done and evaluate how these changes can affect the detection of organic compounds from either gas or particle phase.

L. 15 (also L135): at which m/z is the resolution 14 000 calculated?

L. 16-17 and in the manuscript: I understand the authors want to point how good is the new CHARON FUSION PTR-TOF 10k but the use of “unprecedent” twice in 2 lines is too much (and then through the paper, eg L.21 21 “greater detail”). The purpose is to show the detection of the PAHs and show the capability of the new instrument, which does not require the use many words like “unprecedent” and so on. Please revise the manuscript considering this.

L. 45: not true, see for example Srivastava et al. 2018 (STOTEN)

Introduction: FIGAERO-CIMS technology or EESI orbitrap were not mentioned while they are other technique, which, depending on CI, might detect PAHs at a time resolution lower than typically done with traditional offline filter approach. These technics should be at least mentioned so that the introduction is complete. For instance it is not complete.

L. 114-116 – Figure S1: The time response of the CHARON FUSION PTR-TOF is shown on figure S1 and shows that 10 % of the signal is still there after 31 s. What would be interesting instead is showing the time required to reach background. In other words what is shown here is that measurement at time resolution lower (i.e. faster) than 30 s is not possible due to the time response of the instrument.

Was the time response tested for other compounds (especially heavier? More oxygenated ? PAHs?)

L. 117-118: the modifications made to the ADL should be explained

L. 119-121: Was the particle enrichment factor estimated for other type of aerosols or organic compound? Just checking it is not affected by chemical composition (should not)

Figure 2: Is the peak system from the average spectra of the entire campaign? I suggest moving these mass spectra of peak systems to SI, it is not essential for the paper, as anyone knowing what a resolution of 14 000 (at which m/z?) means is convinced that most isobars can be separated.

Placing the 9 PAHs on the same figure makes it difficult to read, especially for the ones with low concentrations. I suggest splitting the figure or use log scale.

L. 209:211: It is not clear from figure 2 the time response is “quick” as the authors wrote. It took ca. 20 minutes for signal to reach back a low concentration after the peak observed the 09/18 at 23:00, which can reflect the real decay of the plume in the atmosphere, or this plume event might only be few minutes, and the rest is due to memory effect. If the authors do not have an external measurement (NOx for example) to confirm the observed trend on figure 2, I am not sure the authors can claim a real fast time response.

L. 215-217: these lines re explain the instrument capability, which was quite clear based on previous section. These lines are not necessary.

L. 224-225: the choice of 10 factors solution should be supported by a figure showing that adding more factors do not better explain variance. Therefore, examples of tracers used to identify the sources should be included.

L. 231: I suggest adding the sum of 10 factors and residual to SI.

L. 237-241: Naming this aged OOA is questioning as it contains significant amounts of PAHS, that are reactive compounds (Atkinson and Arey, 2007). They should be low in this factor if it corresponds to aged air mass. Wind speed and direction would help to confirm this is an aged OA factor.

Figure 4: it is very difficult to see something on the right panel. Maybe a log scale can help better visualize concentration variations

L. 257: Please be more precise and give numbers for the contribution of these 3 factors to the PAHS.

Conclusion: Finally, out of 4000 ions, only 9 were analysed as PAHs. Are potentially other PAHS present? Or PAHs are a very minor contributor to summer OA in Innsbruck?

L. 276-279: rather than ending on a future campaign of the research group, which is not appropriated for research paper in an international peer reviewed journal, it would be interesting to conclude on the possibilities offered by the new instrument, and the potential new scientific findings or field that are opened with the capability of the new instrument.

Minor Comments

L.134: I was curious to know why the upper m/z limit was so specific (719) ?

L. 162: please specify the software or code language used for source apportionment (NMF etc.)

Please make sure abbreviations are all explained

References:

 Deepchandra Srivastava, Sophie Tomaz, Olivier Favez, Grazia-Maria Lanzafame, Benjamin Golly, et al. Speciation of organic fraction does matter for source apportionment. Part 1: A one-year campaign in Grenoble (France). Science of the Total Environment, 2018, 624, pp.1598-1611. 10.1016/j.scitotenv.2017.12.135. ineris-01853324

Atkinson, R., Arey, J., 2007. Mechanisms of the gas-phase reactions of aromatic hydrocarbons and PAHs with OH and NO3 radicals. Polycycl. Aromat. Compd. 27, 15–40. https://doi.org/10.1080/10406630601134243