This paper is publishable, except that I would like to request one editorial change.
In your response to Reviewer 2's question about snowpack photochemistry on the original page 3647, lines 21-23, you stated "...HNO3 and HONO are also known to deposit to snow...".
It is also known that HONO is emitted from sunlit snowpacks, e.g. as discussed in Zhou et al. (GRL, 2001). This fact impacts the next part of your addition to the paper, in which you state "...a surface depletion of HO2 radicals would be expected". However, snowpack photochemistry is highly complex and while few emission fluxes have been measured, it is easy to hypothesize the reverse (HO2 being enhanced at the surface) as HOx precursors such as HONO and HCHO will be emitted from the snowpack. You might want to cite the appropriate studies from places like Summit, Alert, and Barrow about emission of HOx and NOx precurors from sunlit snowpacks, and be a bit more equivocal about the impact on HO2 near the surface. With this addition/change, the paper will be accepted.