## Advanced / Configuration Setup / In-Line Conversion Modules

Setting the ICHEM variable to a non-zero value changes the model's internal configuration in terms of how it treats the pollutants. Some conversion options require additional modules and specific requirements in setting up the CONTROL file. See the linked discussion under each option for more information.

ICHEM is chemistry module selection index:

- 0=none (DEFAULT)
- 1=Restructure the concentration grid to a source-receptor format
- 2=Convert species #1 to species #2 at 10% per hour
- 3=Enable the PM10 dust storm emission algorithm
- 4=Force concentration grid to be identical to meteorology grid
- 5=Deposit particles rather than reducing their mass
- 7=Transport deposited particles on the ocean surface

Additional Chemistry Options

MAXDIM is the maximum number of pollutants that can be attached to one particle. Otherwise, if multiple pollutants are defined they are released as individual particles. This feature is only required with chemical conversion modules, which are not part of the standard distribution. However, the species 1->2 conversion option will automatically set MAXDIM=2, but the standard emissions routine will still put each species on a different particle in its appropriate array element. The only emissions routine that is enabled to release multiple species on the same particle is the emissions file option. Setting MAXDIM greater than one forces all the species on the same particle, with the limitation that the number of defined pollutants must equal MAXDIM. No other combinations are permitted. The advantage of this approach is that not as many particles are required for the calculation as in the situation where every pollutant is on its own particle. The limitation is that each species on the particle should have comparable dynamic characteristics, such that they are all gases or have similar settling velocities; otherwise the transport and dispersion simulation would not be very realistic.

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