The EU directive 96/62/EG (1996) includes the basic principles for an EU strategy on air quality. In the directive it is stated that measurements have to be made in urban areas of more than 250 000 inhabitants, in zones where the limit values are exceeded and in zones where concentration levels are lower than the limit but exceed a certain upper assessment threshold, given as a percentage of the respective limit values for the pollutants.

In order to achieve as good knowledge as possible of the air quality in different parts of the respective countries, measurements and modelling should be combined. When a first assessment is completed, a combination of models and measurements can be used in areas where concentration levels are lower than the upper assessment threshold. If concentration levels are higher, measurements are required. If the levels are considerably lower, that is below the lower assessment threshold, modelling is enough to determine the air quality.

For the specific pollutants, daughter directives are worked out. In a first step, so-called position papers have been completed for sulphur dioxide, nitrogen oxides, particles and lead. Recently work has begun to establish limit values and to write position papers for benzene and carbonmonoxide. In appendix 1 the EU limit values for SO₂ and NO₂ are presented.