(36)For zones where conditions are particularly difficult, it should exceptionally be possible to postpone the deadline for compliance with the air quality limit values in cases where, notwithstanding the implementation of appropriate pollution abatement measures, acute compliance problems exist in specific zones. Any postponement for a given zone should be accompanied by a comprehensive air quality roadmap to be assessed by the Commission. In such a case, the air quality roadmap should set out appropriate measures to keep the exceedance period as short as possible. Member States should also demonstrate that the measures in their air quality roadmaps have been implemented to ensure compliance.