Thank you for your careful revisions of your manuscript to address the referees’ comments. As the referees’ questions have been largely answered through your reply and revisions, and as the referees were both of a positive opinion regarding your manuscript, it can now be accepted for publication in ACP.

Below I have a few comments you might consider incorporating to improve the clarity of your paper before final publication.

First, regarding Figure S3 (formally S1), I agree with the authors that it is fine to leave this in the Supplemental as the key panels have already been included in Fig. 5 in the main paper.

Page 13, line 451: “Field studies have also produced varying results.” is a rather vague statement. Could you better elaborate here?

Page 13: To more completely discuss INP from carbonaceous aerosol, you could include a brief discussion regarding INP from biomass burning, as you briefly mention biomass burning INP later in the paper. This would be valuable as some biomass burning fuels have been found to emit much more efficient INP than are emitted from fossil fuel combustion.
You could also clarify that some of the wide variability in the INP efficiency of combustion soot aerosol comes from experiments using unrealistic soot particle mimics – elemental carbon particles generated by graphite spark discharge are much more efficient ice nucleants than realistic fossil fuel combustion soot particles are, for example. This has caused persistent confusion in the literature regarding the freezing properties of combustion soot.
To complete the discussion of possible relevant INP sources to your measurement site, you could briefly discuss the recent measurements of INP emitted from agricultural activities.

A comment regarding the use of sodium as a marker for marine INP influences. If the marine INP are caused by certain marine organic carbon components, these organics will tend to be concentrated in the smallest submicron marine sea spray particles, which contain much less Na+ (see Prather et al., PNAS, 2013, for example). Thus using the [Na+] mass concentration may not be a great tracer for marine INP sources. Your additional use of MSA as a marine aerosol tracer may help to address this.

Figure 2: I noted that the HYSPLIT back-trajectories ended at a height of 5.5 m agl, to correspond with the measurements made. Be aware that running HYSPLIT this close to terrain can cause issues as the trajectories can literally run into the terrain, causing a loss of information and less accurate calculated trajectories. While I doubt this would seriously change your computed trajectories and your conclusions, you might consider running your trajectories further above ground level, while still in the surface layer or low in the planetary boundary layer. There is some discussion of these terrain issues on NOAA’s HYSPLIT forums.

Figure 6: I was confused as to what “total particles (e)” referred to. This is the total number of particles > 500 nm counted by the WIBS?

There was also a sketch of a figure I think mistakenly added to the end of the file.


I look forward to seeing this manuscript published in final form in ACP.

Ryan Sullivan