Overall this is a solid paper describing the HETEAC aerosol optics/mixing model that is used to aid in EarthCARE algorithm, development.  As the authors note, EarthCARE is unique among satellite systems in its high degree of multi sensor integration in deriving aerosol products. Therefore, algorithm developers need a beginning baseline to ensure all of the systems are using compatible models. In and of itself, I think the paper does exactly what it sets out to do: explaining the model, the rationale for why they made the decisions they did, and provide some theoretical uncertainties.  From a science reviewer point of view, there is not much to say.   Given this is a baseline, they are keeping it all rather simple at this point.  They are projecting against the major sources in a logical manner and compare well with observations and existing optical models such as OPAC.  I only suggest minor revisions in a few areas.  Going through the paper, I made many notes when the authors massively oversimplified the discussion.  I am ok with a simple model as necessity dictates, but the authors need to be clear what the implications of the simplifications are so users can sequester uncertainty.  However, the conclusion covers nearly all of my distress (no longer necessary to write them down here)-especially on mixing state which I was most concerned about (which makes the section not really the conclusions).  So the paper is at times at odds between declarative statements made throughout, and then in the conclusion waving the hands. Therefore, my only suggestion is to move a lot of that material forward, and perhaps make it an early section.   State essentially that for necessity, you have a simple model, but simple models are, well, simple.   That is ok with what you want to do. Other minor things that the authors may want to emphasize is 1) these models probably will not be great for haze events such as in China or India; 2) use of the lidar ratio is dependent on having a good  retrieval, which for lower concentrations is not a given; and 3)  practically “dusty smoke” have long been the CALIOP’s go to for “We don’t know what this is really.”  How will you handle such uncertainty across platforms.  Other than these I wish the authors well.