A generator for the production of sulfuric acid-coated diesel soot aerosols

Diluted diesel engine exhaust was mixed with sulfur trioxide and the resulting acid-soot aerosol characterized. The generation system, which is suitable for inhalation toxicology studies, was characterized at a soot concentration of approximately 0.5 mg m^-3 and H²SO⁴ coating levels from 0 to 5 mg m^-3. Aerosol characterization included measurement of particle size (cascade impactor + electrical aerosol analyzer tandem sampler) and acid-soot association (electron microscopy of BaCl₂-coated sample grids). The mass distribution of both acid-coated and uncoated diesel soot was unimodal and approximately lognormal. The acid coating increased both the size and monodispersity of the soot aerosol. The mass median Stokes equivalent diameter and geometric standard deviation were 0.12 μm and 2.4 for the uncoated soot, and 0.28 μm and 1.9 at 5.0 mg m^-3 H₂SO₄. Approximately 95% of the soot particles were coated with H₂SO₄; the remainder appeared uncoated. Some H₂SO₄ droplets without a visible nucleus were also observed.