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This paper describes the appearance of wildfire smoke at the United Kingdom at around the same time as an ash cloud was expected from Raikoke volcano in the Kurile Islands.  The distribution and composition of the clouds were analyzed from satellite and lidar measurements, and the Met. Office dispersion model NAME was used to compare the simulated and observed arrival times.  The different clouds could not always be distinguished based on composition, e.g. from particle depolarization ratios in lidar, and so model simulations were required to distinguish them.

The study takes advantage of the rare opportunity to compare ash-cloud simulations with real data over Europe.  And the presence of a smoke cloud adds a twist and makes the study unique and highly worthy of publication.  The paper is well written, figures are clear and well explained, and the inferences seem to be well supported by the data. 

I have made comments throughout the attached pdf.  None point to any significant flaws.  The most significant of the minor comments are below:

1. In Section 3.1.2, the source of plume height and height-mass distribution of ash, used to model ash transport at Raikoke, is said to come from a report at https://wiki.earthdata.nasa.gov/display/volres. I was unable to find a report at that site.
2. In Figure 5, the caption doesn’t seem to match the figure. 
3. Line 312 and earlier: what particle density are you assuming when converting lidar backscatter data to particle concentrations?  How does uncertainty in this value affect uncertainty in concentration?
4. Line 184: it's not clear how the stacked cylinders in Fig. 1b define the source mass release in NAME.  Does each cylinder release the same number of particles?  Do particles originate from random locations within each cylinder?

I look forward to seeing the paper officially published.

Larry Mastin

This paper presents a study combining NAME model simulations with satellite and ground-based observations to determine the composition and origin of aerosol plumes over the United Kingdom. This involved analyzing the long-range transport of stratospheric aerosol in the Northern Hemisphere and the optical properties of the aerosol to identify the source of aerosol from biomass burning by wildfires in Canada, as well as volcanic ash and volcanic sulfate aerosol from the Raikoke volcanic eruption in June 2019. Finally, both signals could be well separated from each other using the described technique.

The paper is well written and I have mostly minor comments on the figures and technical corrections. I have made some technical notes in the attached pdf file.

General comments:

I have a question to clarify the implementation of emissions in your model simulations: You used "a series of stacked and staggered cylinders" to implement the vertical emissions from the forest fire. If I understand you correctly, you are using a column above the volcano with a vertical SO₂ emission profile from the first paper, but not individual cylinders as for the forest fire emissions? You also used a vertical profile for volcanic ash implementation. But I can't find a vertical profile for the implemented forest fires. So how did you scale the 0.1 Tg of material released in each cylinder? Could you briefly describe how you calculated the mass, size, height and position of these cylinders? Could you also provide a vertical profile for the implementation of the forest fires, similar to Figure 2?

Specific comments:

p.15 l. 325: The value 25 µgm^-3 does not fit the scale in fig. 5c.

Figure 4 and Figure 7: For some people, it might be difficult to distinguish between these colors: 0; 7; 9; 10

Figure 5: The caption does not belong to figure 5 -> figure 6.

Figure 8b: Panel 8b is not described in the text. What is panel 8b (volume depolarisation ratio) needed for?

Figure 11: The units in figure 11 are log10 VDR [AU] and log10 RCS [AU], but in the text you use PDR [%]. Maybe you might highlight the most important spots, as in Figure 5, to clarify the description in the text on p. 24-26.

Technical corrections:

You mix different spellings of sulphate/sulfate in the text e.g. p. 7 l.176/177. In part 1 paper you used sulfate.

End all captions of figures and tables with: “.”

Check that there is always a blank between the value and the unit.

Title: part 2: In the first part of your study you wrote: ... - Part 1: ...

p.6 Table 1: double parenthesis ((1999); “blank” between (2007), used

p.7 l.156: “blank” between Raikoke eruption

p.7 l.172: No reference for de Leeuw et al. (2021). Do you mean 2020?

p.8 Figure 2 l.4: the SO₂ product

p.9 Table2: at 532 nm

p.12 l.252: cm³

p.13 l.261: right-hand column

p.13 l.271: SO₂

p.13 l.278: “blank” 532 nm

p.14 l.320: “blank” 13 km

p.19 l.379: 57°N and 60°N

p.19 l. 393: Petzold et al., (2007)

p.20 figure 7: “blank” 532 nm

p.22 figure 8: [m^-1sr^-1]

p.22 l.408: 77°N are out of range of figure 6.

p.23 figure 9: [number per cm³]

p.25 l.436: panel A

p.25: Check the parenthesis of your citations.

p.27 table 5: Formatting: X km for each entry

References: Please double check the format of your references ONE BY ONE to make sure they are in the ACP reference format: e.g. n/a–n/a, two web links, …