Review of ACP-2022-587, Easterbrook et al., Measurement of Henry's law and liquid-phase loss rate constants of peroxypropionic nitric anhydride (PPN) in deionized water and in n-octanol

This paper reports measurements of the solubility and first-order reaction rates of propionyl peroxynitrate (PPN) in water and n-octanol, and limited measurements of the solubility of acetyl peroxynitrate (PAN) in water. The data were then used to estimate atmospheric lifetimes of PPN against heterogeneous uptake in a number of scenarios. The measurements are solid and were well explained. I have only a few minor comments that need to be addressed and the paper should be acceptable for publication.

Line 45. It is not possible to make a blanket statement that the OH rate constants of PANs are low since MPAN (methacrylyl peroxynitrate) and APAN (acryloyl peroxynitrate) have unsaturated R- groups and are known or estimated to react rapidly with OH (Orlando and Tyndall, 2002; Orlando et al., 2002). The statement is true for PAN and PPN, but would benefit from having a range of lifetimes mentioned here.

Line 138. The mixing ratios noted here are quite high. Do they refer to the mixing ratios at the exit of the sources, or the entrance of the reactor. Most GC/ECD systems are limited in linearity at the high end. The technique used in this work relies on the detection scheme being linear with concentration over the range used in the experiment. How do you know your GC systems were linear at the highest mixing ratios used?

Line 155. The same idea as above, you need to justify the assumption of linearity.

Line 180. Instead of the word “known” here, the word “estimated” seems more appropriate.

Line 189. Was it possible to estimate H and k for ethyl nitrate? It looks like there is plenty of signal/noise for that peak.

Line 208 and Figure 5. The authors show, but do not explain points from Raventos-Duran et al., which appear to be estimates from structure-additivity relationships? This needs to be explained in the text.

Line 244. The Tables show lifetimes of 5 and 9 days, which are more than “several days”

Line 259. It would be useful to have the Kames and Schurath number for 278.15K in the table so we can see for ourselves.

Line 299. I think the authors mean “lipophobic” not “lipophilic”. Lipophilic fragments would tend to react with n-octanol.

Lines 312-314. There is a difference in PAN and PPN lifetimes against uptake in marine fogs. However, the difference in thermal decomposition rates will be a bigger effect because of the shorter timescales over which thermal decomposition happens.  

Table 1. The numbers from Burkholder et al are based on the Kames and Schurath work, so are not independent. Moreover, the uncertainty given by Burkholder et al seems inappropriately high. This may be due to the custom in chemical kinetics evaluations of assigning extra uncertainty when there is only one measurement reported in the literature.  

References

Orlando, J. J. and Tyndall, G. S.: Mechanisms for the reactions of OH with two unsaturated aldehydes: Crotonaldehyde and acrolein, J. Phys. Chem. A, 106, 12252-12259, 2002.

Orlando, J. J., Tyndall, G. S., Bertman, S. B., Chen, W., and Burkholder, J. B.: Rate coefficient for the reaction of OH with CH₂=C(CH₃)C(O)OONO₂ (MPAN), Atmos. Environ., 36, 1895-1900, 2002.

Easterbrook et al. measured Henry's law constants and liquid-phase loss

rate constants of PAN and PPN. The manuscript is well-written, and I

recommend publication in ACP after several minor issues have been dealt

with.

- I think the introduction is too long. In particular, I don't think it

  is necessary to discuss the enthalpy and entropy of solvation, as they

  aren't even used in the rest of the manuscript. It should be

  sufficient to say that the parameters A_H, B_H and C_H are used to

  describe the temperature dependence.

- Please specify what temperature and pressure you are referring to when

  you use "sccm". There are many so-called "Standard" values, see

  https://en.wikipedia.org/wiki/Standard_temperature_and_pressure and

  https://en.wikipedia.org/wiki/Standard_cubic_centimetres_per_minute

- Line 125: FEP should not be called "Fluorinated ethylene propylene

  teflon" because it is not teflon.

- Line 138: The recommended symbol for gas-phase mixing ratios (mole

  fractions) is x, not c.

- Line 153: I would call the step from Eqn. (5) to Eqn. (6) an

  integration, not a rearrangement.

- Line 160: The quantity in Eqn. (7) should be called a "ratio", not a

  "fraction".

- Eqn (7): The factor "L" in this equation makes sense only if [X]_l and

  [X]_g are defined in a suitable way. Most likely, [X]_l refers to the

  volume of the air parcel, not to the liquid volume. Please provide the

  definitions of [X]_l and [X]_g.

- Line 238: Why is a different definition of the liquid water contents

  used here than in Eqn. (7)? For consistency, I suggest to use only one

  version of the liquid water contents.

- Line 304: I suggest to replace "have units of years" by "are on the

  order of years". The unit chosen for a quantity doesn't say anything

  about its magnitude.

- Line 318: Change "This work has shown the H constants..." to "This

  work has shown _that_ H constants..."

- Data availability: ACP requests depositing data in reliable public

  repositories. I don't think that providing data data upon request is

  sufficient:

  "Copernicus Publications requests depositing data that correspond to

  journal articles in reliable (public) data repositories, assigning

  digital object identifiers, and properly citing data sets..."

  

  (https://www.atmospheric-chemistry-and-physics.net/policies/data_policy.html)

- Figs. 5 and 6: If your plot program allows it, it would be nice to add

  a second x-axis at the top of the plot, showing T in addition to

  1000/T.

- Tab 1: It should be mentioned that, unlike the other entries in this

  table, Burkholder et al. (2020) is a literature review.

- Tab 1: Since calculated data from Raventos-Duran et al. are already

  shown in Fig. 5, I think that they should also be mentioned in Tab. 1.

  Note that there is another publication with calculated Henry's law

  constants, including PAN and PPN: 10.5194/acp-17-7529-2017

- It is nice to see that the authors are following the new IUPAC

  recommendations. However, a very minor comment is that lower case

  superscripts should be used for c and p because these are the symbols

  for concentration and pressure, respectively.

- The Engauge Digitizer is not sorted alphabetically in the list of

  references.