The Canadian

Centre for Environmental Modelling and Chemistry

Evaluative Level I, II, III Fugacity Models


This series of BASIC models treat the partitioning of a specified organic chemical in an evaluative environment with an area of 1 km2 at 25 oC. Each Level has two versions, one with an environment of only air, water, soil, sediments (designated "a"), the other with the additional media fish and suspended solids (designated "b").

This series of models 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. The Levels provide a progression of understanding.

A more detailed description of all three Levels is included in the text "Multimedia Environmental Models; The Fugacity Approach" by D. Mackay, Lewis Publishers, CRC Press. 1991 on pages 67-183.

Windows users may prefer the friendlier Visual Basic EQC model which treats all Levels.

Level I

This program estimates the equilibrium partitioning of a quantity of organic chemical between the homogeneous environmental media with defined volumes, densities, organic carbon contents, and lipid fraction. There are no in- or out-flows of chemical, and no degrading reactions occur.

We recommend that Windows users try the new Visual Basic Level I model.

The required input data are:
Chemical Properties:

  • chemical name
  • molecular mass
  • temperture
  • water solubility
  • vapour pressure
  • log Kow
  • Amount of chemical

    Model output includes:

  • overall prevailing fugacity of the system
  • partition coefficients
  • Z values
  • concentrations and amounts in each compartment

  • Level II

    This program is similar to the Level I described above, but is a steady state model with a constant input rate, rather than single dose of chemical. There is both advective in- and out-flow of chemical from the unit world. Chemical losses can also occur through degrading reactions.

    In addition to the data required for Level I the following must be input:

  • emission rate in place of amount of chemical
  • advective inflow rates
  • inflow concentrations
  • reaction half-lives in each medium

  • Model output now also includes:

  • D values
  • reaction and advection loss rates
  • residence times
  • Level III

    This program does not assume an equilibrium state, but only steady state. The program uses conventional expressions and typical parameters for intermedia transfer by processes such as wet deposition from the air, sediment deposition in the water, and soil runoff. If intermedia transfer rates are not known, use the BASIC Generic model which assumes a set of transfer rates.

    In addition to the data required for Level II the following must be input:

  • emissions, and advective inflow rates and concentrations to each medium
  • intermedia transfer rates

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

    Model output now also includes:

  • fugacity of each compartment
  • System requirements to run the compiled programs are minimal. The entire series is included in a single, self-extracting, downloadable file.

    Please read the LEVEL I, II, III 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 10, 2013.