Air quality plans - Article 23
Introduction
Directive 2008/50/EC fixes limit values for some air pollutants. After the expiration of all transition periods and possibilities for Member States to postpone their application, these limit values have applied all over EU since 1 January 2015. The limit values may not be exceeded when they are measured in conformity with the requirements of Directive 2008/50/EC.
Where such an exceedance of a limit value or target value of Directive 2008/50/EC occurs, the Member State in question must establish an air quality plan in order to bring air pollution down to limits of the limit value or the target value. The exceedance period must be kept as short as possible. When limit values of several pollutants are exceeded, an integrated air quality plan shall cover all the pollutants, "where appropriate".