The Canadian

Centre for Environmental Modelling and Chemistry

EQC (Equilibrium Criterion) Model

Version 1.01 (16-bit) - May 1997

A more recent version of this model is also available. Version 2.00 Released May 2003

Chemical-physical properties are used to quantify a chemical's behaviour in an evaluative environment in this Visual Basic model. The evaluative environment includes the following compartments: air, water, soil, sediment, aerosols, and suspended sediment. Three types of chemicals are treated: chemicals that partition into all media (Type 1), involatile chemicals (Type 2), and chemicals with zero or near-zero solubility (Type 3). Levels I and II assume thermodynamic equilibrium is achieved; Level II includes advective and reaction processes. Level III is a non-equilibrium, steady state assessment.

This model is useful for establishing the general features of a new or existing chemical's behaviour, ie. the media into which the chemical will tend to partition, the primary loss mechanisms, and its tendency for intermedia transport. The result of various emission scenarios can be explored.

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

A more detailed description of the model is given in the three paper set:

  • Mackay D, Paterson, S., Kicsi, G., Di Guardo, A., Cowan, C.E. "Assessing the Fate of New and Existing Chemicals: A Five Stage Process". Environ. Toxicol. Chem. 15 No.9 , 1618-1626, 1996.

  • Mackay D, Paterson, S., Di Guardo, A., Cowan, C.E. "Evaluating the Environmental Fate of a Variety of Types of Chemicals Using the EQC Model", Environ. Toxicol. Chem. 15 No.9, 1627- 1637, 1996.

  • Mackay D, Paterson, S., Kicsi, G., Cowan, C.E., Di Guardo, A., Kane, D.M. "Assessment of Chemical Fate in the Environment Using Evaluative, Regional and Local-Scale Models: Illustrative Application to Chlorobenzene and Linear Alkylbenzene Sulfonates" Environ. Toxicol. Chem. 15 No.9, 1638-1648, 1996.

    • The required input data are:
    Chemical Properties:

  • chemical name
  • molecular mass
  • reaction half-lives in each of air, water, soil, and sediment
  • for Type 1 chemicals:

    • - data collection temperature
    - melting point
    - water solubility (g/m3)
    - vapour pressure
    - log Kow
  • for Type 2 and 3 chemicals:

    • - partition coefficients

    Environmental Transport Velocities:

  • air side air-water mass transfer coefficient
  • water side air-water mass transfer coefficient
  • rain rate
  • aerosol deposition rate
  • soil-air phase diffusion mass transfer coefficient
  • soil-water phase diffusion mass transfer coefficient
  • soil-air boundary layer mass transfer coefficient
  • sediment-water diffusion mass transfer coefficient
  • sediment deposition
  • sediment resuspension
  • soil-water runoff rate
  • soil-solids runoff rate

    • Emission Rates:

  • emissions to any or all of air, water, and soil

    • Model output for each Level as appropriate includes:

  • partition coefficients for Type 1 chemicals
  • Z and D values
  • fugacity of the system or of each compartment
  • concentrations and amounts in each compartment
  • residence times
  • a summary diagram
  • various summary graphs


    • This program is only available in compiled form. The equations are the same as those in the fugacity models. To run this program you will need a computer running either MS Windows 3.1 or Windows 95. The zipped file is 891KB and is self-expanding to about 2.78 MB.

    Please read the EQC 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 August 12, 2011.