Dear authors,

First of all, I would like to thank the two reviewers. I believe their comments were very constructive and they rightfully pointed out some of the limitations of your tagging methodology and its non-physical effects.

Reviewer 1 pointed out a number of points in relation to your methodology (consider of nox-limited or voc-limited regimes, non-physical effects, equal weighting to nox and voc precursors, tagging to a chemical family etc..). In particular, the reviewer wanted some of the limitations and non-physical effects to be discussed before publication. Having read your responses and your revised manuscript, I believe that you have adequately addressed this reviewer's concerns.

Reviewer 2 also pointed out the need for further explanation (factor of 0.5, production of NMHCs from methane) and again, I feel that this has been addressed adequately. However, I also felt that there was a misunderstanding by the reviewer of what the tagging method was diagnosing. In particular, it was not diagnosing the effect of an emissions reduction on ozone but rather diagnosing the contribution of a particular emissions source to ozone. Indeed, I felt that you were very clear in the introduction of the differences between a "contribution" and a "perturbation" approach and showed how they are used to answer different questions.

As a result, on balance, I am happy to recommend that your manuscript be accepted for publication in Geoscientific Model Development.

Some minor spelling mistakes:
1. Pg 20, line 591: developping -> developing
2. Pg 21, line 607: extend -> extent

Regards,
Fiona O'Connor