The report gives an overview and proceedings of the 2009 workshop on PM2.5 organized by the Netherlands Environmental Assessment Agency (PBL) in cooperation with TNO. The aim of this workshop was, given the European standards for PM2.5, to discuss with a number of European experts the current state-of-knowledge concerning all aspects of PM2.5. This means observations, emissions, modelling, source apportionment and health effects.
Countries have started to include measurements of PM2.5 and its components in their national air quality monitoring networks. Harmonization of the national air quality networks is on its way but takes a considerable amount of effort. As a consequence it is difficult to make a consistent view of PM2.5 Europe wide. Policy assessments which aim at finding adequate conditions for compliance to the PM2.5 standards are therefore still very uncertain. In addition there is growing evidence that, like PM10, also PM2.5 is a rather crude indicator for the health effects associated to particulate matter. So it is necessary to design smart policies which aim at the health improvement and take at the same time the current uncertainties into account about the efficiency of the PM2.5 air quality standards for health improvement.