Dear Authors,

I read through the revised manuscript and contacted the reviewers to get their feedback on your response. Summarizing all the comments, I suggest the following minor revisions given below. If those are addressed I am happy to accept your manuscript for publication. Just as a note, I did not receive or were able to look at Corbin et al. papers in press or submitted. If you could send me the Corbin et al. AST paper, this would be beneficial for the evaluation.

With kindest regards,

Daniel Knopf

Minor revisions:
1. Regarding “In SP-AMS mode, 1064nm Light-absorbing Refractory PM (LR-PM) is heated to vaporization by the continuous-wave laser. Due to this heating, any internally-mixed material which is refractory below the LR-PM vaporization temperature may also be vapor- ized. In this study, the LR-PM was rBC, which vaporizes at 4000K (Schwarz et al., 2006; Moteki and Kondo, 2010), so that non-refractory PM (NR-PM, here mostly OM; Corbin et al., 2015a), ash, or BC surface functionalities (Corbin et al., 2015c) are vaporized when internally-mixed with rBC.”
The thermal vaporizer is not turned off in SP-AMS mode. Thus, in “SP-AMS mode” it is actually LR-PM that is detected along with both internally mixed NR-PM and externally mixed NR-PM. Without knowledge of the mixing state of the particles with respect to light-absorbing components, it is not possible to know the extent to which internally vs. externally mixed NR-PM contributes to the observed signals, which can be important as the fragmentation patterns may differ. This can be resolved by adding a sentence such as: “Any NR-PM that is externally mixed from the LR-PM components may still be vaporized by the thermal vaporizer, and thus the detected signals in the SP-AMS are a sum of those from refractory and NR-PM components that are internally mixed with LR-PM and of any NR-PM that is externally mixed from LR-PM.”

2. Discussion regarding CO+: The sentence “These values are consistent with literature-based expectations (Corbin et al., 2015a).” requires a different/additional reference, specifically to the literature from which the literature-based expectations come, not to the publication that discusses the methodology employed here and described further in that publication. Since the AS&T paper is not available, there remain some general concerns regarding the ability to quantitatively separate CO+ from N2+, especially when operated in “V” mode.

3. It is not entirely clear why dilution with synthetic air would make the correction smaller than that needed for atmospheric measurements. By “synthetic air” do the authors mean “a mixture of N2 and O2 and Ar, free from other impurities including CO2”? If this is the case, then shouldn’t the CO+ background be similarly smaller than needed for atmospheric measurements?

Technical corrections:
It is recommended the authors change “As discussed extensively in an earlier publication (Corbin et al., 2015a),” to “As discussed extensively in a separate publication (Corbin et al., 2015a),”

The reference to Bruns should be updated to the AMT reference (not AMTD). Similarly, the AMTD paper submitted by Corbin should be updated to the full reference.

Section 2.4.2: Check fonts at “~2 μg m-3“

Section 3: Section title, keep it just as “Results”

Section 3.2.1: Change “Previous work by our group…” to “Another study by our group…” or equivalent. A few lines below a period is missing after “Fig”.

Section 4: It is unusual to have 2 results sections and either title as is, is not very explanatory. I suggest having this section as 3.3 will a full section title. It does not make the reading of the paper more difficult.

Section 5 would then be section 4, etc.

A grammar note: In general, “which” should be used after a comma, while “that” is used to connect thoughts that do not require a comma. Although not universally true, the “comma-rule” can get one quite far.

Would it be possible to indicate the (CO+) detection limit in Figs. 3d and 5b (and 4d and 6d) in the figure (as horizontal line) or give the number in text or figure caption?

Figure caption 3 and 4: Typo in “H2O+”.

Dear Authors,

I am happy to accept your manuscript for publication in Atmospheric Chemistry and Physics.

With kindest regards,

Daniel Knopf