Dust Emission Schemes with MOSAIC

Hi
I am using WRF-Chem v3.8.1 with CBMZ gas-phase and MOSAIC-VBS aerosol mechanisms. When I checked the code "module_mosaic_addemiss.F", there are two dust emission schemes coupled with MOSAIC [dust_opt = 2 & dust_opt = 3 which have been changed to 13 in WRF-Chem v3.9.1].
My questions:
- What is dust_opt = 13 coupled with MOSAIC? Is it a simple GOCART or GOCART-AFWA? When I looks through the code and from my literature reading, it looks like simple GOCART. But it is confusing me when they said dust_opt =3 in the source.!!!!
- How can I modify the code in "module_mosaic_addemiss.F" for dust_opt = 2 which is DUSTRAN (Shaw et al., 2008) according to the dominated vegetation types over my study region because it works well for dry season over Mexico.
I figure out that I should modify Part 1 - compute vegetation mask in the ”module_mosaic_addemiss.F” source code (highlighted in yellow: the soil types over the study region) but I don’t know how according to what I should change the fractions of the Olson vegetation classes (f8, f50, f51, f52) for each soil type.

Part 1 - compute vegetation mask
alphamask=0.001
if (ivgtyp(i,j) .eq. 7) then
f8=0.005
f50=0.00
f51=0.10
f51=0.066
f52=0.00
alphamask=(f8+f50)*1.0+(f51+f52)*0.5
endif
if (ivgtyp(i,j) .eq. 8) then
f8=0.010
f50=0.00
f51=0.00
f52=0.15
f52=0.10
alphamask=(f8+f50)*1.0+(f51+f52)*0.5
endif
if (ivgtyp(i,j) .eq. 10) then
f8=0.00
f50=0.00
f51=0.01
f52=0.00
alphamask=(f8+f50)*1.0+(f51+f52)*0.5
endif

Regards,
Siham