Dear authors,

After having a reviewer go through your manuscript here are the different points you need to improve upon before I consider its publication:

Here are the reviewer's comments:
'I’ve read through the attached document (their replies to the reviewer comments and their changed manuscript). Overall, I am happy with the way they addressed my comments and those of the second reviewer . I certainly think this manuscript should eventually be published, but I still feel that, at times, the writing style is too poor and too qualitative for ACP standards. There is an experienced co-author on the paper, so there’s no excuse here to my mind. I have added some comments on the attached .pdf, My main quibble is about their sentence saying that pollution increased by up to 50 ug/m^3 (lines 4-6 abstract) this is not true and the authors state that later themselves (lines 1-2 on page 4 of their revised paper in the attached document). They explain in the reply to my comment that they excluded these stations, but to my mind that cannot be a valid reason to state in an abstract that pollution reached up to 50 ug/m^3 because I think people agree that the pollution episodes (> 500 ug/m3) in Ireland on 6 Sep 2014 are linked to Holuhraun.'

So, Michael should attentively address the style and consider where the text is too qualitative.

Considering this sentence:
“Surface observations in Europe showed concentration increases up to 50 μg/m3 averaged over an
hour of SO2 from volcanic plumes passing.”
the reviewer wrote the following comment:
in Ireland SO2 surface concentrations increase to over 500 ug/m3 on 6 Sep 2014. I don't understand this sentence nor is it very specific. The authors should state the period of observation and location. I assume they are not talking about the volcanic pollution episode on 6 Sep 2014 as otherwise the 50 ug/m3 is too low.

Does the terminology 'basic (bas)' in the sentence below refer to the baseline simulation?
"The control simulation is renamed basic (bas). From the observed heights, and emission fluxes given
elsewhere, this simulation is the “best guess” simulation."

In the following text:
“For the first six day period, between 20 to 26 September, high concentrations of SO2 were measured
over Great Brittain, and countries to the south. For the second six day period,"
please add 2014 behind September. The manuscript needs to be checked for such things throughout.

With respect to this statement:
"The detailed information will be included in the manuscript. The high SO2 concentration observed
over Ireland on 6 September did not show up on many of the station that we were able to collect, so it
was left out of the manuscript, but two Irish stations are shown in Figure 3."
The reviewer had the following comment:
I don't understand why this is a reason to leave out these data. several stations in Ireland detected high SO2 pollution and backward and forward trajectory analysis shows that it is volcanic pollution.

Please rephrase the sentence below that the reviewer deem is neither correct, nor good english:
"Surface observations in Europe showed peak type concentration increases up to 50 μg/m3 averaged over an hour of SO2 concentrations from volcanic plumes passing by and lasting only for a short time."

"The eruption ended in February 2015 and during the 6 months of eruption a total of approximately 11 (± 5) Tg SO2 may have been released (Gislason et al. 2015), and the total lava field from the fissure were 85 km2 with a volume of 1.4 km3 (vedur.is)."
Check wording, is the word area missing from this sentence?

THe authors introduced the changes requested by on reviewer and improved the subtantially the text.
Please make the following minor changes before the paper can be published in ACP.

In the abstract, please be more clear about what you mean by a 'three months average SO2 and PM2.5 concentrations' in the following sentence:
'On three month average over Europe, SO2 and PM2.5 surface concentrations increase, due to the volcanic emissions, increased by only ten anqdand six percent over Europe, respectively.'
Do you mean that the PM2.5 concentrations increased during a particular 3-months period? If this is the case, indicate exactly the period. If not, clarify what you meant.

Change 'exceedances days' to 'exceedance days' in the abstract


Sorry it took me a long time to get to review this version of the paper.

Sincerely,

Yves Balkanski