Since WRF v3.6 there is an option to have a micro-physics scheme with awareness on aersol densities. See more details in Thompson Aerosol-aware.
One need to add at WPS - metgrid, the files with the climatologies of aerosos. These climatologies come from GCM runs where aerosols where active. There are 3 different climatologies (QNWFA_QNIFA_Monthly_AWIP/GFS/ERA), comming from the ue of 3 different re-analysis.
In case of using ERA-Interim re-analyses, on should include on the <code<namelist.wps