Levels A, B, C, etc. are analogous to Levels 1, 2, 3, etc. used for satellite observations.
For real data you start from the observed "radiances" (Level 1), perform a retrieval (Level 2), 
then grid them (Level 3), or assimilate them (Level 4). 
So as not to get confused, for the simulated data, we use Levels A, B, and C.

Level A:  What we start with, the fundamental gridded model fields, aerosol physical and optical properties, and surface characterization (BRDF, NDVI, etc.), on their respective native grid.  Most people will not be interested in this, and the really large files may be archived elsewhere.

Level B: Model fields and BRDF sampled at the satellite location. Here you will find the mixing ratios, air density, RH, and BRDF kernels all sampled at the satellite footprint.

Level C: The simulation of the instrument observabls. 
For lidar, extinction and backscatter profiles - aeronet-g5nr.lc2.ext.YYYYMMDD_HHz_LAMBDAd00nm.nc4. 
For the polarimeter, the polarized reflectances - aeronet-g5nr.vlidort.vector.YYYYMMDD_HHz_LAMBDAd00nm.nc4. 
We also included in this file other derived aerosol optical properties such as SSA, effective radius, index of refraction, aerosol volume and surface area, etc., for the particular mixture that exists at that particular location and time. In this sense, index of refraction and effective radius are dynamic, depending on the mixing state and ambient relative humidity.