This paper extends traditional surface layer similarity to fog and aerosol layers where the particles have a constant gravitational settling velocity (Vg). Neutral and stable situations are considered. The result is a correction to traditional Monin-Obukhov (MO) profiles, which consist of a logarithmic profile + a stability function dependent on z/L, where z is height above the surface and L is the Obukhov length. A new dimensionless number Vg/(k u*) is introduced, where kappa is the vonKarman constant and u* is the friction velocity. This number characterises the relative importance of gravitational settling and turbulent flux. The merit of this paper is that it provides analytic solutions for profiles of liquid water content or aerosol concentration in the surface layer. They do not only depend on z/L as in traditional MO-similarity but also contain a dependency on Vg/(k u*). Although the analysis is limited to neutral and stable situations, the work is highly relevant for practical application in numerical weather prediction, because advection of fog over water with flow from warm to cold SST, leads to stably stratification and to fog formation once the air becomes saturated. The work is also highly relevant for aerosol modelling not in the least because it provides a framework to put widely used schemes for deposition velocity in the framework of MO similarity. The idea as presented in this paper is innovative, and will not only help to analyse data from profile measurements in fog and aerosols, but it will also help to formulate surface transfer laws in models. Surface transfer of fog droplets and aerosols is a highly sensitive component of models, but at the same time very uncertain. I therefore welcome this paper as it will inspire observational work and provide a framework for the analysis of observations. This is the only way forward to reduce uncertainty in models. 

I have no hesitation to recommend this paper for publication in its current form. The paper is innovative, well written, well embedded in relevant literature, and highly relevant for practical applications. Turbulent deposition of fog droplets is largely ignored in models (by lack of supporting science), so I hope it will inspire the science community to pay more attention to turbulent deposition of droplets and aerosols. 

Minor comments: 

1. Line 240

Reference is made to radiation fog over land as an example of fog with stable stratification. It would be good to mention advection fog over water where fog forms in a transition from warm to cold SST. 

I have the following comments for the author to consider in the revised version of this manuscript.

Abstract can be expanded a bit to include more detailed descriptions of the major findings and results.

Introduction provides a good discussion on the history of the similarity theory, which is based on constant flux layer situations in steady state. Cases under neutral stratification were discussed. May be the author can also provide a brief discussion on how the theory was expanded to unstable stratification, for a complete picture on this topic. The last paragraph in Introduction may be reorganized a bit so the readers can easily find out what materials are from existing theory, what are to be proposed in this study, the major goals of this study, and/or an outline of the following sections.

Line 125: delete “(i.e. not involving rain or snow - wet deposition)” to avoid confusion. This is because dry deposition happens all the time, even during precipitation events. As long as the pollutants are not incorporated into hydrometers before being adsorbed by surface, this process is referred to as dry deposition.

Line 130: add particle sizes for each scenario: “If gravitational settling is the main cause of FQc (e.g., for particles large than several micrometer), we would expect little change in Qc with height, but if turbulent transfer is dominant (e.g., for very small particles) then the choice of zref could be important”

Lien 148: This is my biggest concern of this study. Is this Rs defined here the same meaning as that in Zhang et al. (2001)?  If so, then Rs cannot be assumed to be 0. In any particle dry deposition model, Rs can never be 0, and actually is very large over water surface (Rs is usually >> Ra under unstable and neutral stratification, and on a similar magnitude to Ra under stable stratification).

Because all of the following sections are based on this assumption (Rs=0), which I do not agree with, I do not have much confidence on all the results generated here.  If not setting Rs as 0, is there a way to still generate some analytical formula? I guess not.

If section 3 was based on a false assumption (i.e., Rs=0), and if the author cannot fix the error, then this section should be deleted from this manuscript. To make the study still publishable, the author can change the study to a “Short communication” and then focus on Section 2 only. If possible, expand Section 2 to cover all stratification conditions over water surface, and if possible, provide some recommendation on how to expand to other land surfaces (smooth ones first and then vegetated surfaces).