This report is one of a series of ten titles that deals with pollutants suggested to EPAQS by the Department of the Environment, Transport and the Regions, the Scottish Executive, National Assembly for Wales and the Department of the Environment in Northern Ireland. The reports normally consider individual pollutants except where the Panel decide to deal with more than one because of the relationship between pollutants. Key features of the reports include: evidence of the effects of air pollution on human health and of progressive development of the air quality monitoring network; discussion of the appropriate measurements on which to base an airborne particles standard in the UK; and sections on sources, chemical and physical characterization, personal exposure, mechanisms of action and epidemiology of particles.