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

42

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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