Principles of modelling

For many impact assessments, releases of contaminants into the environment have to be modelled, because suitable data do not exist (e.g. where assessments are prognostic and need to estimate future releases under a specified scenario). 

The detailed structure of release models varies depending on the source type, contaminant, environmental medium (e.g. air, water or soil) into which release occurs, and details of the application (e.g. spatial scale, time scale).  The basic formulation, however, remains the same:

R = S * F

where, R is the release rate (mass or volume/time), S is the level of source activity (/time) and F is the emission factor (mass or volume/unit of activity). 

The term F  can be further expanded, where appropriate, to take account of emission controls inherent in the source:

F = E * (1-R/100)

where E is the emission rate and R is the emission efficiency (i.e. percentage of emissions removed/withheld by the emission control device).

Data inputs

Information on source activity can be obtained either from the available statistical information, or by modelling (see link to Contaminant sources in panel to left).  Established emission factors are also available, for a wide range of source activities and contaminants, derived from direct monitoring of typical sources, from experimental studies or from analysis of input and output data for individual processes.  These may allow for recognised emission control technologies; otherwise, estimates of emission effciency need to be derived from independent sources (e.g. test results from technology providers). 

Links

A range of release models have been developed for different pollutants and environmental media.  LInks to a selection of models and model factsheets are available in the Model section of the Toolkit.