Questions on optical property calculations in AeroCom phase II models with the purpose of a correct interpretation of diagnosed AOD properties in the AeroCom database:

1) Do you assume and how internal mixing when computing optical properties of total aerosol? Is Size varying? Which mixing assumption?

2) Do you differentiate between clear-sky and all-sky relative humidity and which one do you use for the AOD calculation, reported to AeroCom?

2b) If you differentiate, have you investigated the difference?

3) Is the reported-to-AeroCom AOD as asked under 2) used directly for the RF calculations?

4) Would you consider the diagnosed AOD provided to the Aerocom database as representative for clear-skies? Eg for comparison to Aeronet and satellite retrievals in clear skies?

5) If you diagnose a clear-sky AOD ⇒ How do you compute it? What are the assumptions on RH? Any threshold of RH you use? Cloud fraction weighting to derive a monthly average Clear-sky AOD?

6) Which humidity growth factor and variation do you use ? How does it depend on RH? Do you include sub-grid variability in relative humidity?

7) Do you diagnose the aerosol water mass or aerosol water AOD? How?

8) Is the diagnosed sea salt and sulfate AOD computed at ambient RH? And eventually is that using clear-sky or all-sky RH?

9) Do you average nighttime and daytime values of AOD into daily averages?

10) What is the single-scattering albedo of your BC, POM, DUST? Does it vary as a function of size, RH? How roughly? Which range?

11) What is the absorption coefficient of BC? How is it calculated?

12) Please provide the refractive index at 0.55 microns for each aerosol species? And eventually further information on the hygroscopicity for each species.