This was very interesting to read. Please find my comments attached. 

The manuscript explores the impact of ship emissions to a campaign-based Arctic cloud scene through large-eddy simulations. To mimic various ship exhaust technologies and their emissions, the authors impose aerosol particle size distributions informed by previous laboratory work and find microphysical responses that slightly alter clouds’ condensate amount and emitted longwave radiation.

The overall manuscript is well written. I have a couple of concerns that the authors should address before publication.

Major concerns

The title suggests a wider picture on Arctic clouds, but the manuscript focusses on a particular case. It is unclear, whether these results are representative for the wider Arctic. The authors should (1) put the selected case into perspective by using cloud statistics from Arctic observations, and (2) discuss potential impacts to clouds that have not been touched on here. I wonder if there are other cases of stronger cloud-aerosol-precipitation interaction, where the various aerosol scenarios make a more meaningful difference. Perhaps it also necessary to change the title to: “Potential impacts of marine fuel regulations on an Arctic stratocumulus case and its radiative response”.

The description of simulations lacks important details: (1) Looking at Christiansen et al., (2020), there is a large-scale divergence imposed – is that the case here, too? (2) Furthermore, the authors show the vertical temperature profile and indicate that it’s kept constant – is that achieved through nudging or advective tendencies and is either technique applied throughout or only in the free troposphere? (3) The authors should also specify how they calculate turbulent surface fluxes. (4) How do the authors justify imposing ship-based aerosol uniformly rather than only within the marine boundary layer?

The authors show a significant difference in longwave emissions but none in the shortwave spectrum. The latter is puzzling to me, and the authors should elaborate on why that is – are there perhaps compensating effects of cloud fraction and cloud albedo?

Minor concerns

ll. 108-110 Would it be possible to provide satellite imagery of this case (or at least coordinates) so that readers can obtain a visual impression of the case?

ll. 136ff (and also Fig. 1) It took me a while to understand the scenarios and their number of modes (and would expect the same for other readers). Perhaps it would be simpler to display all initial aerosol size distributions in Fig 1. I’m also not sure I understand the value of Fig. 1b – perhaps its better suited in the appendix?

l. 191 The label “mix” is confusing and should instead be labelled as “no ship”.

l. 381 “smaller” is ambiguous here.