The Canadian

Centre for Environmental Modelling and Chemistry

Level II Model

32-bit Version 2.17 - September 1999
16-bit Version 2.1 - September 1998

A Level II simulation describes a situation in which a chemical is continuously discharged at a constant rate and achieves a steady-state and equilibrium condition at which the input and output rates are equal. Degrading reactions and advective processes are the loss or output processes treated. Intermedia transport processes (eg. no wet deposition, or sedimentation) are not quantified. The medium receiving the emission is unimportant because the chemical is assumed to become instantaneously distributed to an equilibrium condition.

Physical-chemical properties are used to quantify a chemical's behaviour in an evaluative environment. Three types of chemicals are treated in this model: chemicals that partition into all media (Type 1), involatile chemicals (Type 2), and chemicals with zero, or near-zero, solubility (Type 3). The Level II Program assumes a simple, evaluative environment with user-defined volumes and densities for the following homogeneous environmental media (or compartments): air, water, soil, sediment, suspended sediment, fish and aerosols.

This model is useful for establishing the general features of a new or existing chemical's behaviour. A Level II calculation gives an indication of the likely media into which a chemical will tend to partition and an indication of relative concentrations in each medium. The distribution between media is the same as in Level I. The results of changes in chemical and environmental properties may be explored.

Three persistences are calculated, an overall value, TO, and individual persistences attributable to reaction only, TR, and advection only, TA. Note that 1/TO equals the sum of 1/TR and 1/TA.

Consideration of advection and reaction rates allows for the calculation of chemical persistence. It provides a first estimate of overall environmental persistence, which is a critical property of the chemical. It also shows which loss processes are likely to be most important. A fast reaction or short half-life may not be significant if relatively little of the chemical is subject to this reaction by virtue of its partitioning. The potential for the chemical to be subject to long-range atmospheric transport is also indicated by the magnitude of the air advection loss. The global chemical persistence is best indicated by the reaction persistence, whereas the local persistence is indicated by the overall persistence.

Note that in this version, reaction half-lives are requested for all 7 media. In previous versions reactions in only 4 media were treated. The advective residence time selected for air also applies to aerosols and the residence time for water applies to suspended sediment and fish. The advective residence time of aerosols, suspended sediment and fish cannot be specified independently of the air and water residence times.

A Level II calculation is more realistic than a Level I calculation but requires additional information.

Features of the Level II Program:
Provides a database of chemicals and chemical properties.
Permits temporary additions/changes of chemicals and their properties to a simulation.
Permits permanent additions, changes and deletions of chemicals and their properties to the chemical database.
Supplies default values for all input fields which may be easily changed. These values match those in the EQC model.
Provides context-sensitive Help.
Displays and prints the Level II model calculations, as performed by the program.
Allows the printing of simulation tables and the summary diagram.
Allows the program results to be saved as an ASCII text file.

This program was based on the following publication:

Mackay, Donald (1991) "Multimedia Environmental Models: The Fugacity Approach" Lewis Publ., CRC Press, Boca Raton, FL.

The required input data are:
Chemical Properties:

  • chemical name
  • molecular mass
  • data temperature
  • reaction half-life estimates for

  • - air
    - water
    - soil
    - sediment
    - aerosols
    - suspended sediment
    - aquatic biota
  • Type 1 chemicals

  • - water solubility
    - vapour pressure
    - log Kow
    - melting point
  • Type 2 and 3 chemicals

  • - partition coefficients

    Environmental Properties:

  • volumes for all media
  • densities for all media
  • organic carbon content (soil, sediment & suspended sediment only)
  • fish lipid content (Type I chemicals only)
  • advective flow residence times for air (including aerosols), and water (including suspended sediment and aquatic biota)
  • advective flow residence time for sediment burial
  • Emissions:

  • chemical input rate
  • inflowing concentrations in air and water
  • Model Output:

  • partition coefficients (Type 1)
  • Z values
  • fugacity of the system
  • D values
  • reaction and advection loss rates
  • residence times or persistences (overall, reaction, and advection)
  • concentrations and amounts for each compartment
  • a summary diagram
  • This program is only available in compiled form. A "readme.txt" file with more detailed technical information is included in the zipped file.

    The 32-bit version 2.17 requires at least a Pentium-75MHz with 8 Mb of RAM running Windows 95. The monitor should be set to SVGA (800 x 600) resolution. The zipped file is 3.6 MB and requires about 12.5 MB of hard disk space to install.

    The 16-bit version 2.1 requires at least a 486DX-50MHz with 8 Mb of RAM running MS Windows 3.x. The monitor should be set to standard VGA (640 x 480) resolution. The zipped file is 3.0 MB and requires about 11.5 MB of hard disk space to install.

    For non-Windows users the BASIC, evaluative, Level I, II and III fugacity models are available.

    Please read the LEVEL II SOFTWARE LICENSE before downloading the software. Use of the software constitutes your agreement to abide by the terms and conditions set out in the license agreement.


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    Last updated June 12, 2013.