Recital 54

(54)Since the objective of this Directive, namely to set out air quality provisions with the aim to achieve a zero-pollution objective, so that air quality within the Union is progressively improved to levels no longer considered harmful to human health, natural ecosystems or biodiversity, cannot be sufficiently achieved by the Member States by reason of the transboundary nature of air pollutants, but can rather, by reason of its scale and effects, be better achieved at Union level, the Union may adopt measures, in accordance with the principle of subsidiarity as set out in Article 5 of the Treaty on European Union. In accordance with the principle of proportionality as set out in that Article, this Directive does not go beyond what is necessary in order to achieve that objective,