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 (e.g. 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 model assumes a simple, evaluative environment with user-defined volumes and densities for the following homogeneous environmental media (or compartments): air, water, soil, sediment, suspended particles, 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 persistence are calculated, an overall value, TO, and individual persistence 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 particles and fish. The advective residence time of aerosols, suspended particles 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 and charts.
- Allows the program results to be saved as a comma separated value (.csv) file readable by most spreadsheet software.
This program was based on the following publication:
Mackay, D. 2001. "Multimedia Environmental Models: The Fugacity Approach - Second Edition", Lewis Publishers, Boca Raton.
The required input data are:
Chemical Properties
- Chemical name
- Molar mass
- Data temperature
- Reaction half-life estimates for
- Air
- Aerosols
- Water
- Suspended particles
- Aquatic biota
- Soil
- Sediment
- For Type 1 chemicals
- Water solubility
- Vapour pressure
- Log Kow
- Melting point
- For Type 2 and 3 chemicals
- Partition coefficients
Environmental Properties
- Volumes for all media
- Densities for all media
- Organic carbon content (soil, sediment, and suspended particles only)
- Fish lipid content
- Advective flow residence times for air (including aerosols), and water (including suspended particles and aquatic biota)
- Advective flow residence time for sediment burial
Emissions
- Chemical input rate
- Inflowing concentrations in air and water
Model output includes
- Partition coefficients (Type 1)
- Z values
- Fugacity of the system
- D values
- Reaction and advection loss rates
- Residence times or persistence (overall, reaction, and advection)
- Concentrations and amounts for each compartment
- A summary diagram and charts
This program is only available as an Excel spreadsheet, and is in "beta" testing. Please send any comments or problem reports to Mark Parnis
The Basic Level II Model Version 3.00, released September 2005 continues to be available below.
Please read the 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.