The chemical composition of atmospheric ultrane particles

Atmospheric ultra› ne particles (with diameter less than 0.1 m m) may be responsible for some of the adverse health e¬ects observed due to air-pollutant exposure. To date, little is known about the chemical composition of ultra› ne particles in the atmosphere of cities. Ultra› ne particle samples collected by inertial separation on the lower stages of cascade impactors can be analysed to determine a material balance on the chemical composition of such samples. Measurements of ultra› ne particle mass concentration made in seven Southern California cities show that ultra› ne particle concentrations in the size range 0.056{0.1 m m aerodynamic diameter average 0.55{ 1.16 m g m i3 . The chemical composition of these ultra› ne particle samples averages 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 in the ultra› ne particles are Fe, Ti, Cr, Zn, with Ce also present. A source emissions inventory constructed for the South Coast Air Basin that surrounds Los Angeles shows a primary ultra› ne particle emissions rate of 13 tonnes per day. Those ultra› ne particle primary emissions arise principally from mobile and stationary fuel combustion sources and are estimated to consist of 65% organic compounds, 7% elemental carbon, 7% sulphate, 4% trace elements, with very small quantities of sodium, chloride and nitrate. This information should assist the community of inhalation toxicologists in the design of realistic exposure studies involving ultra› ne particles.