Overview

This page is part of the Chemical Model (CHEM) documentation.
It contains a description of CHEM including the topics aerosol compounds

Description

All parts of 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 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, areosol 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).

A main factor influencing atmospheric chemistry are the emissions of reactive compounds. In PALM-4U emissions can be applied in three different ways:

• PARAMETERIZED: Traffic emissions are parameterized depending on the the values of street_type in the static file. Emission values for each street type and chemical compound must be supplied in the namelist as described below. No other emissions are considered. street_type can be obtained from OpenStreetMap.
  
• DEFAULT: Gridded yearly emissions must be supplied by the user as specified in the PIDS document (see sample emissions file). Typical temporal variations are apllied by PALM4U.
  
• PRE-PROCESSED: Preprocessed hourly (other temporal intervals will be possible in later versions) 3-d emission fields must be supplied by the user.

Importantly, for the DEFAULT and the PRE-PROCESSED mode of the emissions, the exact date of the start of the simulation must be indicated through the namelist parameter date_init of the date_and_time_mod module.

IMPORTANT: In the PRE-PROCESSED 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 in the corresponding attached document here.