4. Evaluating existing assessments

Member States may have existing data on air quality for some or all zones and

agglomerations. The Guidance document should also provide criteria for Member

States and the Commission to judge whether such existing information is sufficient

for a preliminary assessment (FWD, Article 5), or whether additional work should be

carried out.

There are three main assessment tools. Besides measurements emission inventories

and model calculations are used to describe the air quality (van Aalst et al., 1997).

Assessment of air quality is an important issue in many areas, especially in the urban

environment. The most credible, complete and useful assessment is obtained by

combining measurements and modelling results. The monitoring at chosen sites

provides data on air quality and its temporal variability. Dispersion models extends

the knowledge by computing concentration fields as a function of time at various

spatial scales. Under the Directive, if air quality is close to the limit value modelling

alone can not, and may not, be used to assess the air quality situation and exceedances

of air quality standards.


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