Article 2.5.2.3.1. The necessary measures shall be taken to ensure that in zones and agglomerations where the levels of sulphur dioxide, nitrogen dioxide, PM10, PM2.5, lead, benzene and carbon monoxide in the air are lower than the respective limit values stated in Appendices 2.5.3.11 and 2.5.3.14, the levels of these substances are kept below the limit values, and that efforts are made to protect the best air quality compatible with sustainable development.