The Commission has issued in 2005 a proposal for replacing the current Framework Directive on air quality and its first three daughter directives by a single new directive on ambient air quality. The proposal responds to the high priority given by the Thematic Strategy on Air Pollution to regulating PM2.5 in order to reduce the severe health risks associated with this component of particulate matter. One of the proposed changes is the adoption of an exposure reduction target for PM2.5, a new type of standard which, combined with a binding concentration cap, aims at delivering more substantial benefits in terms of population exposure, compared to the traditional approach. The directive also addresses certain difficulties that Member States are experiencing in implementing the existing directives. This concerns in particular the questions of where limit values apply and how to deal with natural sources of particulate matter when establishing compliance with limit values and the introduction of the possibility for extending, under strict conditions, the time frame for meeting limit values. This paper summarises the main elements of the existing directives, experience of its implementation in Member States and proposed changes. At the time of writing the paper, the proposal was under negotiation in Council and Parliament.