Dust emissions are calculated online in the Land Model. The method is currently being updated: https://github.com/ESCOMP/CTSM/issues/1604
A global dust emissions tuning factor is set in CAM (atm_in): dust_emis_fact
To change the dust emissions in your simulation, add dust_emis_fact to your user_nl_cam.
The dust_emis_fact is applied as dust emission flux / dust_emis_fact, so to reduce emissions from a previous run, increase the dust_emis_fact value.