GEM does not calculate or advect aerosols. However...

‘cccmarad’ considers the following 5 types of background Aerosol Optical Depth/Thickness (AOD/AOT):

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

The AOD can be different for all model levels.

GEM:

By default, GEM uses hardcoded background Aerosol Optical Depth/Thickness (AOD/AOT).

• 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 red line in image below
• 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 blue line in image below
• 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.

CRCM6-GEM5:

In CRCM6-GEM5 one has the possibility of reading prescribed 2-D background AODs for all 5 types of aerosols, which will then get used by 'cccmarad2'. The fields can vary in time, but so far only 2-D fields can get read. As when using the default AOD, they will be distributed evenly (in term of meters) over all model levels of the planetary boundary layer.