The chemical composition of atmospheric ultrafine particles

Atmospheric ultrafine particles (with diameter less than 0.1 mum) may be re sponsible for some of the adverse health effects observed due to air-pollut ant exposure. To date, little is known about the chemical composition of ul trafine particles in the atmosphere of cities. Ultrafine particle samples c ollected by inertial separation on the lower stages of cascade impactors ca n be analysed to determine a material balance on the chemical composition o f such samples. Measurements of ultrafine particle mass concentration made in seven Southern California cities show that ultrafine particle concentrat ions in the size range 0.056-0.1 mum aerodynamic diameter average 0.55-1.16 mug m(-3). The chemical composition of these ultrafine particle samples av erages 50% organic compounds, 14% trace metal oxides, 8.7% elemental carbon , 8.2% sulphate, 6.8% nitrate, 3.7% ammonium ion (excluding one outlier), 0 .6% sodium and 0.5% chloride. The most abundant catalytic metals measured i n the ultrafine particles are Fe, Ti, Cr, Zn, with Ce also present. A sourc e emissions inventory constructed for the South Coast Air Basin that surrou nds Los Angeles shows a primary ultrafine particle emissions rate of 13 ton nes per day. Those ultrafine particle primary emissions arise principally f rom mobile and stationary fuel combustion sources and are estimated to cons ist of 65% organic compounds, 7% elemental carbon, 7% sulphate, 4% trace el ements, with very small quantities of sodium, chloride and nitrate. This in formation should assist the community of inhalation toxicologists in the de sign of realistic exposure studies involving ultra fine particles.