I have read the response to the reviewers comments and revised manuscript
and can see that the authors have made a great deal of effort to address the
reviewers comments and suggestions.

The discussion on the timescale for SO2 chemical conversion after very large
volcanic eruptions, and the sensitivity experiments to test the effect of
Van Der Waals forces in accelerating the rate at which particles coagulate,
both represent valuable additions to the author response and the
revised manuscript.

However, I found the third addition to the revised manuscript, around
the discussion of the tropical stratospheric warming hard to follow and
out of scope. The reviewer's motivation for suggesting the potential was
to "test your aerosol radiative heating code", but the title of the paper is to
assess the stratospheric aerosol simulated by the model. The
warming anomaly from satellite observations represents a combination
of several signals including QBO variation, simulated aerosol properties,
and dynamical composition changes. That the model simulations are
nudged to meteorological re-analyses fields also futher complicates matters.

I find that whole section added in the revised paper to be out of scope and
request it be removed, ensuring the paper remains focussed on the topic
stated in the title.

Together with this major revision, I also have two minor revisions
which I strongly suggest the authors make to improve the manuscript.

Once these 3 sets of changes have been made, I expect the manuscript
to be ready for publication, without requiring further referees comments.
However, given the changes requested, I would ask to see the revised
paper before it be allowed to proceed to publication.

1) For the reasons above, please delete the text on page 3 (lines 4 onwards)
and page 4 entirely, and replace with a brief reply that given the stated
topic of the paper, assessing the warming is out of scope. The additions
added replying to the other two suggestions are already considerable and
sufficient. In the revised manuscript, please remove the two
paragraphs added to page 17.

2) The sensitivity simulations added to assess the Van Der Waals effects on
coagulation are valuable additions to the paper. A minor change of emphasis
is however required which I have made specific suggestion for below.
There is one minor required change to the manuscript, and then a series
of minor edits to the reply to reviewers required, which are important
given the wider relevance for the strong sensitivity to the coagulation
rate change the results indicate, and in light of the transparent review
process.

The change to the reply to reviewers, relates the statement "we have now
applied the parameterization of the enhancement factor of Chan and
Mozurkowich (2001)". The authors explain in the previous sentence that
they have not done that, and the text needs revising here. I am specifically
suggesting a series of minor wording changes to the sentences beginning
"In additional sensitivity tests...." that will together achieve this. Firstly,
replace "In" with "However, in" so that the sentence then follows logically
from the previous one. Second, replace "have now applied the parametrization"
with "test the above two limiting values of". Third, replace "(2001)" with
"(2001, equations 29 and 30)" to be clear on the source of the expression.
Fourth, replace "We perform two additional simulations" with "The experiments
involved". Finally, to make the rest of that sentence clearere, remove the
text "a first one with coagulation enhanced uniformly by the factor E(0) and
a second one" and finally replace "the factor E(infty), which is generally
larger than" with "the factors E(0) and E(infty), which are 1.25 and 2.27."

The text added to the actual revised manuscript requires only one
minor change to rephrase "only few measurements on" with
"only few measurements to constrain" (since the Van der Waals enhancement
cannot be observed directly).

3) On page 14 (1st sentence of section 3.1), state what the climatological
values for COS and SO2 are that are applied as a lower boundary condition.

Now that the authors have made the requested changes, I am now
content for the paper to proceed to publication in GMD provided
the following two very minor changes (in reply to the last set of
revisions that were made in version6 of the manuscript):

1) One of my comments requested "...and finally replace
"the factor E(infty), which is generally larger than" with
"the factors E(0) and E(infty), which are 1.25 and 2.27."

The authors replied, "We changed the text of the response accordingly,
except for the last point. The values of 1.25 and 2.27 are only valid for
colliding particles of identical size and for a certain temperature. But we
used the size and temperature dependent parametrization of E(0) and
E(infinity), which we now clarify in the text."

The request above was based on giving the reader some indication of
the size of those enhancement factors E(0) and E(infty).

Although I take the point that it would not have been correct to specify
the values "are 1.25 and 2.27.", I do still feel it important to state these
values -- but for the authors to add the extra few words they gave in
their explanation above -- so instead to say "are 1.25 and 2.27 for
colliding particles of identical size and for temperature T0" where
the value of the reference temperature T0 should be given explicitly.

That will then help the reader understand the magnitude of these
enhancement factors (i.e. that the Van der Walls forces can accelerate
the coagulation rates by between +25% and +127%) -- for the same
sized particles at that reference temperature.

2) I checked the manuscript and it looks like the authors forgot to
make one of the changes they agreed in their response to my Editor
Review to make. See I said:

"The text added to the actual revised manuscript requires only one
minor change to rephrase "only few measurements on" with "only few
measurements to constrain" (since the Van der Waals enhancement
cannot be observed directly)."

And the authors said:

"We changed the sentence accordingly."

But I checked and that sentence still has the original wording.
Perhaps it was simply a case that the authors forgot to make that change?

Once those two changes I am happy to proceed to publication in GMD.

The authors have made the final two very minor revisions I requested.
I am therefore happy to approve the manuscript to be published in
the main journal Geoscientific Model Development.