== Overview ==
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[[NoteBox(note,This page is part of the **Aerosol Model** (SALSA) documentation. \\ It contains a description of SALSA. \\ For an overview of all SALSA-related pages\, see the **[wiki:doc/tec/aerosol SALSA main page]**.)]]

The aerosol module SALSA ([wiki:doc/app/salsaref/ Kokkola et al., 2008]) embedded in PALM ([wiki:doc/app/salsaref/ Kurppa et al., 2019]) can be used to simulate the aerosol particle concentrations, size distributions and chemical compositions. In SALSA, the aerosol size distribution is represented as a discrete set of size bins (by default 10 bins). 
The number n,,i,, (m^-3^) and mass concentration m,,c,i,, (kg m^-3^) of each size bin i and chemical component c are the model prognostic variables. Currently, the following chemical components can be included: sulphuric acid (H2SO4), organic carbon (OC), black carbon (BC), nitric acid (HNO3), ammonium (NH3), sea salt, dust and water (H2O). Furthermore, the gaseous concentrations of H2SO4, HNO3, NH3 and semi- and non-volatile organics (OCNV and OCSV) are also default prognostic variables. 
The aerosol dynamic processes included are
 * coagulation,
 * condensation of H2SO4, organics (both OCSV and OCNV)) and water vapour, 
 * dissolutional growth by HNO3 and NH3, 
 * nucleation and dry deposition on horizontal and vertical surfaces and resolved vegetation. 

SALSA can be coupled with the [/wiki/doc/app/chempar#chemistrymodule "chemistry module"]. In that case, the five gaseous compounds (H2SO4, HNO3, NH3, OCNV and OCSV) will be imported to SALSA from the chemistry module and should thus be included in the chemical mechanism applied ([https://palm.muk.uni-hannover.de/trac/browser/palm/trunk/UTIL/chemistry/gasphase_preproc/mechanisms/def_salsa%2Bsimple "Example"] for a chemical mechanism including the gases needed in SALSA).

SALSA is enabled by adding the NAMELIST {{{salsa_parameters}}} with appropriate parameters to the INPUT parameter file ({{{<run_identifier>_p3d}}}).

SALSA can be run with horizontal boundary conditions that differ from the remaining PALM code. For example, it is possible to use non-cyclic boundary conditions for the SALSA variables, while cyclic conditions are used for all other variables. See respective boundary condition parameters like [wiki:doc/app/salsa_parameters#bc_aer_n bc_aer_n].