Dear authors, co-authors,

I finally found the time to carefully check your response to the comments raised by the reviewers on your article on bi-directional exchange of methanol and acetaldehyde submitted for publication in ACP. The comments by reviewer #1 tackle a number of issues and going through your response as well as the suggested revisions, it seems that this helps in overall arriving at an improved version of the ms. Consequently, I decided to accept the ms for publication in ACP after you have tackled this last round of minor editor comments just coming up reading your response and revisions.

In the revised ms version I noticed this feature that should be corrected: Pp 4, lines, 17-19, “While firmly based in plant physiology and plant response to environmental conditions, this approach would allow modelslackingleaf-level processestoaccountforthechanges in fluxdirection”

Furthermore add the units after the term 3000, “where Rstom ((μmol m-2 s-1)-1) is the stomatal resistance, 3000 (s m-1) is the model default limiting night time value of Rstom and n is a scaling factor”

I have to say that this discussion on the selection of the values of the nocturnal stomatal resistance is not a strong feature of the paper also since it apparently is also included to represent removal over night by the (wet/dry) cuticle. Generally, choice of this nocturnal (stomatal) resistance term, which should reflect a general complete stomatal closure is rather arbitrary also due to the lack of direct observations. But having a quite high LAI can then even with such a selected large nocturnal value still result in quite some nocturnal removal and impact on simulated concentration also due to the limited mixing volume. Why did you not simply include the Rcut and Rstom terms as parallel resistances as is commonly done in dry deposition calculations and where Rstom (e.g., 1e6) is much higher than Rcut (3000 s m-1) resulting in a nocturnal Rleaf of 3000 s m-1 and a daytime Rleaf dominated by Rstom?

In your response to the reviewers comment on the role of advection, I see your point about the potentially small impact of “anthropogenic” air masses with the winds generally coming from a direction with a small anthropogenic footprint. But what about having a footprint from a natural source region with also substantial biogenic sources of methanol and acetaldehyde? Would there be other ecosystems located more to the north that could also potentially have a large bVOC source?

In your response to the reviewer on issues on the nocturnal decrease in methanol you mention that: “It is most likely due to the lack of an explicit treatment of wet deposition or wash-out within the model. We intend to develop FORCAsT in the future to include a representation of loss of methanol and other water-soluble compounds to wet surfaces based on relative humidity within the canopy as observations suggest this may be an important sink for such compounds”. I agree with this point on the potential role of wet-canopy removal. This might be interpreted as a formality (also since you have not included a reference to this in the paper) but according to my long-term knowledge on the dry deposition process, removal of gases/aerosols by a wet canopy are also seen as a dry deposition process feature and not referred to a wet deposition or wash-out. This is really referring to the process of removal of gases and aerosols by scavenging and rain-out.

Regards, Laurens Ganzeveld

Dear author, co-authors, have checked this last round of minor revisions I accept your submitted paper for publication in ACP. Let's now see how this paper will further trigger research on some of these mechanism's explaining some of the observed bi-directional exchange fluxes,

Regards, Laurens Ganzeveld