Aerosol particles with a wide range of light absorption properties were generated, transported, and characterized to permit meaningful intercomparisons of all the major types of light absorption instruments. The particles were generated in concentrations of ~1 mg m(-3) and 50 microg m(-3) for periods up to 2 h. The particle characteristics ranged from highly absorbing carbonaceous to nearly transparent ammonium sulfate, from submicron ammonium sulfate to supermicron Arizona road dust, and from spherical ammonium sulfate to chain-aggregate carbonaceous and irregular ambient particles.