Congratulations on your manuscript that is accepted for publication in AMT, provided you take into account the following comments.

1. Your statements that trace gas retrievals will improve when including snow-covered scenes are too strong. I agree that the high surface reflectivity is potentially benefitting the vertical sensitivity to NO2 in clear-sky situations. But the reality for all retrievals is that they need highly accurate cloud retrieval schemes that can distinguish between a bright surface and bright, low altitude clouds. I don’t think we have those in place yet. I think this line of thought should be reflected in the text.

P7, L14: …high reflectance is potentially advantageous …

P8, L36-39: clarify that the number of observations and sensitivity improves strictly in clear-sky situations, in reality snow-covered scenes will often be covered by clouds screening the NO2 below.

P17, L295-297: “The increase in AMF … to tropospheric NO2.” is a too strong statement. You should clarify that this is only valid if one assumes that a cloud algorithm will handle the snow-covered scenes with 100% reliability. The quality of information will furthermore only be achieved if the NO2 profile and albedo value are of high quality.

2. You test in the paper the presence of snow – but what about the snow albedo value? In Figure 4, these values are listed as 0.81 and 0.83, but based on what? Adding a bit of discussion on the snow albedo values from the various sets and their uncertainties would be useful.

P14, L211: please rephrase considering that snow albedo values may be quite uncertain and that residual clouds may be present affecting this sensitivity – otherwise the readers may wrongfully conclude “snow means better sensitivity”, whereas the message should be that “under clear-sky conditions and with very good knowledge of snow albedo, the presence of snow means better sensitivity”.

Specific comments:
P9, L65: please add that … are often omitted or flagged as unreliable to avoid potential errors

P17, L302: please add …retrievals over clear-sky reflective snow-free surfaces…

P18, L326: please add …significant impact on retrieved NO2 columns and clouds (Vassilkov et al., 2017; Lorente et al., 2018).

Caption Figure 3: please explain how you obtained the snow reflectance value.

Lorente, A., Boersma, K. F., Stammes, P., Tilstra, L. G., Richter, A., Yu, H., Kharbouche, S., and Muller, J.-P.: The importance of surface reflectance anisotropy for cloud and NO2 retrievals from GOME-2 and OMI, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-32, in review, 2018.

Congratulations on your manuscript that is now accepted for publication in AMT.