Review attached

Peron et al. used eddy covariance measurements of terpenoids and other VOCs to estimate their contributions from anthropogenic and biogenic sources in the city of Innsbruck, Austria.

The paper is an interesting contribution to the emerging subject of volatile chemical product emissions in urban areas, where it is especially challenging to find out how much of the terpenoids is anthropogenic. As such, it is especially important since there are, to date, few analyses of VCP emissions in European cities. The manuscript is well written, and I recommend its publication in ACP after the following comments have been addressed:

General: The paper mentions a lot of correlation analyses that were done for the data analysis but shows none of the plots. I think it would be beneficial to add supplementary material that makes at least the most important correlation analyses accessible and verifiable for the reader.

For the discussion: It would be interesting to compare the derived anthropogenic emissions to emission factors per person used in the literature (e.g. Coggon et al. 2021 use an estimate monoterpene emission factor per person), since the population in the footprint of the authors’ station should be available.

Coggon, M. M., Gkatzelis, G. I., McDonald, B. C., Gilman, J. B., Schwantes, R. H., Abuhassan, N., Aikin, K. C., Arend, M. F., Berkoff, T. A., Brown, S. S., Campos, T. L., Dickerson, R. R., Gronoff, G., Hurley, J. F., Isaacman-VanWertz, G., Koss, A. R., Li, M., McKeen, S. A., Moshary, F., Peischl, J., Pospisilova, V., Ren, X., Wilson, A., Wu, Y., Trainer, M., and Warneke, C.: Volatile chemical product emissions enhance ozone and modulate urban chemistry, PNAS, 118, 1–9, https://doi.org/10.1073/pnas.2026653118, 2021.

l. 39ff: Are these % by mass or molar? This makes an important difference. The first sentence (50% of terpene emissions are isoprene, which means that the other 50% must be monoterpenes+sesquiterpenes) contradicts the second one (15% + 0.5% do not add up to 50%).

l. 44: Unclear: do you refer to total emission strength from plants or of global methanol emissions?

l. 55: It is true that simple models based (just) on future temperatures predict an increase in BVOC terpenoid emissions, but I think the authors should acknowledge that there are other factors that play a role (e.g. increased CO2 inhibits isoprene fluxes), so the situation is way more complicated, as shown in this review: Holopainen, J. K., Virjamo, V., Ghimire, R. P., Blande, J. D., Julkunen-Tiitto, R., and Kivimäenpää, M.: Climate Change Effects on Secondary Compounds of Forest Trees in the Northern Hemisphere, Frontiers in plant science, 9, 1445, https://doi.org/10.3389/fpls.2018.01445, 2018.

As a result, it is impossible to predict how BVOC will change globally with climate change. This is e.g. discussed in the latest IPCC report (Szopa, S., v. Naik, Adhikary, B., Artaxo, P., Berntsen, T., Collins, W. D., Fuzzi, S., Gallardo, L., Kiendler-Scharr, A., Klimont, Z., Liao, H., Unger, N., and Zanis, P.: Short-Lived Climate Forcers, in: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M. I., Huang, M., Leitzell, K., Lonnoy, E., Matthews, J., Maycock, T. K., Waterfield, T., Yelekçi, O., Yu, R., and Zhou, B., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 817–922, https://doi.org/10.1017/9781009157896.008, 2021.)

l. 122 ff: Regarding interferences on m/z 69.07: Firstly, it is commendable that the authors acknowledge the presence of interferences on the protonated isoprene mass. However: Did the authors do their described correlation analysis also just using nighttime data? Given the low isoprene fluxes at night in general, the interference from cooking aldehydes may be more important during the night than on average. I would like to see the respective correlation plots in the Supplement.

An interference of 30% from m/z 87.08 plus an interference of <30% from higher aldehydes seems not insignificant if anthropogenic isoprene is 64% in the spring – given the potential interference discussed by the authors, it could be that a significant fraction of that is actually from an aldehyde interference and thus likely from cooking.

So, at least the percentages given e.g. in the abstract should include uncertainties, and I wish the authors would also consider in the discussion that they may partly see the influence of cooking emissions contributing to anthropogenic m/z 69.07. It would be even better if they could correct their isoprene fluxes for the interference(s).

l. 402: Maybe I am wrong, but wasn’t the R² of 0.48 in Gkatzelis et al. related to population density, not benzene?

l. 478: The Borbon et al. studies were done more than 20 years ago. Are there any newer studies to confirm that cars with modern catalysts still emit isoprene?

l. 482: also fragranced cleaning products?

l. 516: I am missing an explanation/hypothesis as to why the sum of monoterpene fluxes stays the same between spring and summer, but the anthropogenic fraction changes. Do people use less fragranced products in the summer? (Seems a little unlikely to me.)

Data availability: I do not think it is enough to make the data available on request. The authors should upload the final flux data to a publicly accessible server with a DOI. E.g., Zenodo makes this very easy.