In zones and agglomerations where the levels of sulphur dioxide, nitrogen dioxide, PM_{10}, PM_{2,5}, lead, benzene and carbon monoxide in ambient air are below the respective limit values specified in Annexes XI and XIV, Member States shall maintain the levels of those pollutants below the limit values and shall endeavour to preserve the best ambient air quality, compatible with sustainable development.
Article 12 - Requirements where levels are lower than the limit values
Article 12
Requirements where levels are lower than the limit values