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 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.