For the evaluation of possible air quality standards exceedances, the integrated urban
models are the most useful. Single point source models will only provide information
on the contribution from a point source, which is of limited use for a total assessment.
Since traffic emissions will to a great extent determine the urban air quality, street
pollution models are useful to assess the zones at risk for exceedances, and for the
evaluation and extrapolation of measurement results to larger zones. This type of
model is relatively simple and is easy to use. The results are, however, only
indications of the real situations and must be evaluated further using monitoring data
and more advanced models.
Although there are a number of well-established models in use in urban areas in
different parts of Europe, no general recommendation can be made here. However, the
model must fulfil the requirements of QA/QC (see van Aalst, 1997) and be thoroughly
validated against monitoring data.
An increasing demand for air quality assessment is foreseen and will be the driving
force towards further development and improvement of dispersion models. Various
models are needed. Operational models are an important tool for city planning. Online
models are used for air pollution forecasting at pollution episodes to show present
and near-future risks. Models for regulatory purposes are used to demonstrate zones of
compliance/non-compliance with air pollution directives.
To be powerful tools, the models must fulfil certain quality criteria. Work on quality
assurance of models is important and has recently been started within different
organisations. Accuracy can be documented in terms of uncertainties in input
quantities and in model formulation, and could be demonstrated in the validation
process. Reference models will be defined in time. Development, validation and
application of urban models will be carried out within EUROTRAC-2, SATURN.
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