Thank you for your interesting manuscript on a potentially important topic in atmospheric chemistry. After considering reviewers' comments, I find that the identification of ketene is not sufficiently strong from an analytical chemistry point of view. The only clear conclusion from the results is that the abundance of m/z 43.018 is very significant. The laboratory investigation to rule out vinyl acetate is useful and convincing. It is, however, difficult to positively identify ketene as the species behind m/z 43.018. (Ruling out VA is useful, but not sufficient.) While ACP is not an analytical chemistry journal, it is still useful to follow some of the principles for chemical identification. The lack of authentic standards or separations, and the possibility of fragmentation in PTR pose serious problems to the identification. In my view, it would take more to convince readers about the ketene identification.

I understand that more experimental work is useful but just drags out the review process. I propose that the authors reword the manuscript and focus on the observations (i.e. abundance of 43.018 ion with a flux comparable to other well known VOCs) and propose ketene as a possible species, which would be more consistent with the level of certainty in species identification. It is still a useful and important contribution to show that this one ion is representing some unknown species. I am happy to accept a manuscript that conveys this message.