Overview

This page is part of the Chemistry Model (CHEM) documentation.
It contains a description of CHEM including the topics aerosol compounds, deposition and emission.
For an overview of all CHEM-related pages, see the CHEM main page.

All parts of the code that are related to chemistry start with chem_. The main routines and the driver of the chemistry module is included in chemistry_model_mod.f90​, subroutines are in chem_gasphase_mod.f90, chem_photolysis_mod.f90, and chem_emissions.f90.

The chemistry model is automatically activated when a chemistry_parameters namelist is included in the parameter file (<run_identifier>_p3d).

The module chem_gasphase_mod.f90, where the gas-phase chemistry rate equations are solved within PALM-4U depends on the chosen chemical mechanism. chem_gasphase_mod.f90 is generated by a preprocessor that is based on the Kinetic Pre-Processor KPP (Damian et al. (2002), Sandu et al. (2006)), Release 2.2.3 from November 2012 (​http://people.cs.vt.edu/asandu/Software/Kpp/, kpp-2.2.3.tar.gz) and an adapted version of the KPP postprocessor KP4 (Jöckel et al (2010)). This adapted version of KP4 which converts the KPP-generated code to a PALM-4U module is named kpp4palm.

The chemical preprocessor is located in the subdirectory UTIL/chemistry/gasphase_preproc.

Currently, aerosol compounds can be considered either as passive compounds or the sectional aerosol module SALSA (Kokkola et al. (2008)) can be used to simulate the aerosol particle concentrations and size distributions.

Deposition processes are also taken into account in the chemistry model. The deposition of particles is derived following Zhang et al. (2001) while gases are deposited using the DEPAC model following van Zanten et al. (2010).

The main factor influencing atmospheric chemistry is the emissions of reactive compounds. In PALM-4U emissions can be provided by the user in different levels of detail (LOD):

• LOD 0: Traffic emissions are parameterized depending on the values of street_type in the static file. Emission values for each street type and chemical compound must be supplied in the namelist. This option, named ’Parameterized’ mode, is currently only implemented for the traffic sector. No other emissions are considered. street_type can be obtained from OpenStreetMap.
  
• LOD 1: Gridded annual emissions must be supplied by the user as specified in the PIDS document​. A typical diurnal profile based on urban traffic counts is implemented to disaggregate the total emission of the different species to hourly values.
  
• LOD 2: Gridded preprocessed hourly (other temporal intervals will be possible in later versions) emission information that is already temporally disaggregated must be supplied by the user. IMPORTANT: In this mode, the initial date of the simulation has to coincide with the first day for which emission values are available.

Find a more detailed description of the PALM-4U emission input ​here.