Dear authors,

Thank you for your detailed response to the reviewers' comments. I have received further comments from the reviewers, which I copied below. Once these comments are addressed, the manuscript will be suitable for publication in ACP.

Best,
Sally

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Additional comments from reviewers:

The details provided on the OH reactivity instrument are still rather brief although there is a reference to Mao et al. (2009) where further details can be found.

Although in the response the uncertainty in the zero is now stated (0.5 s-1, 2 sigma), the actual zero of the instrument is still not stated, and needs to be as this is a fundamental parameter. Also in the response it is not clear what is meant by "instrument offset"? In the revised manuscript, it states that the "zero" is (0.5 s-1, 2 sigma), whereas should this be the uncertainty in the zero, as stated in the response? This inconsistency needs to be addressed. The zero should be stated with its uncertainty.

Given that uncertainty in the dilution rate is stated in the response to represent the largest source of uncertainty in modelling OVOCs - the amount of material on this point in the main paper ought to be increased (most of the discussion on this important point is in the supplement).

I would recommend that the authors add an additional paragraph to the main text describing the additional results illustrated in Figure S5, as there is little discussion of these results in the main text or in the supplement.

I would also recommend deleting the sentence on page 9 line 16 ("This suggests that the total RO2 production rate and resulting O3 formation are likely well understood") as it detracts from the main conclusions of the paper regarding the ability of the model to reproduce the observed total OH reactivity.

Dear authors,

Thank you for your response to the reviewers’ further comments. I think you have addressed the comments adequately. However, I echoed the suggestion raised by one of the reviewers to delete the sentence “This suggests that the total RO2 production rate and resulting O3 formation are likely well understood”. Specifically, the agreement between modeled total OH reactivity and measurements can suggest that the RO2 production rate from VOC oxidation is well understand, but this does not necessarily suggest that the total RO2 production rate and thus ozone formation are well understood. The model over-predicted isoprene first-generation oxidation products and it was suggested that the largest uncertainty influencing OVOC concentrations is dilution. Nevertheless, as noted in the manuscript, an extremely high dilution rate would need to be incorporated for dilution alone to account for the difference between model results and measurements. As such, this would seem to suggest that some other factors could be at play and that the fates of radicals (thus ozone production) are not fully understood. I suggest either removing this sentence, or keeping the sentence in the manuscript but adding some caveats to reflect some limitations of this statement. Either way, this would not divert the merit of the manuscript. Once this is addressed, the manuscript can be accepted for publication in ACP.

Best,
Sally