GEM does not calculate or advect aerosols. However, the radiation scheme 'cccmarad' uses a predefined background Aerosol Optical Depth/Thickness (AOD/AOT). 

‘cccmarad’ consideres the following 5 types of background aerosols:

• Organic carbon
• Sea salt
• Mineral dust (from deserts)
• Black carbon
• Sulphate

The their AOD can be different for all model levels.

In GEM:

• Organic carbon only exists over land where it’s AOD goes linearly from 0.25 at the equator to 0.05 at the poles – see image 
• Sea salt only exists over the ocean where it’s AOD goes linearly from 0.13 at the equator to 0.03 at the poles – see image
• Mineral dust, black carbon and sulphate are set to zero everywhere

The background AOD is distributed evenly (in term of meters) over all model levels of the planetary boundary layer.

In CRCM6-GEM5:

In CRCM6-GEM5 we now have the possibility of using prescribed 2-D background AODs for all 5 types of aerosols. The fields can vary from one month to the next, but so far only 2-D fields can get used. Although, it should not be that complicated to introduce 3-D fields. 
At the moment we only have a pre-industrial monthly AOD climatology from EC-Earth. But if you find others (for example for current and/or future) we can use those as well. For as long as they are AODs for the 5 types of aerosols cccmarad consideres.
See 2-D AOD plots on next slide.