Key pollutants--airborne particles.

The sources and composition of airborne particles, and trends observed over the past 50 years are reviewed in this paper. Major components of recent samples include elemental and organic carbon, secondary ammonium sulphate and ammonium nitrate, resuspended dust, and soil and sodium chloride. Early measurements employed the black smoke technique. More recently, PM(10) has been the accepted measure and is the basis for air quality standards and limit values. Between 1970 and 1999, a substantial reduction in emissions of particulate matter was achieved mainly through a cut in emissions from commercial, residential, and institutional combustion. Forthcoming European Union standards are likely to require particulate traps on new diesel vehicles.