Direct ultraviolet photoionization electrically charges particles using a mechanism distinct from di usion charging. The purpose of this study is to evaluate aerosol photoemission theory as a function of aerosol particle size, concentration, material, and morphology. Particles are classi ed using an aerodynamic aerosol classi er (AAC) and subsequently measured with a scanning mobility particle sizer (SMPS) and photoionization measurement system in parallel. This con guration allows direct comparison of photo-emission from high concentrations of initially neutral, monodisperse aerosols with di erent morphologies or materials. Under all examined conditions, the overall photoelectric yields of particles of self-similar material (silver and unconditioned soot) and morphology (sintered spheres and agglomerates) are each linearly proportional to the second moment of the mobility-equivalent diameter distribution, even in the transition regime (mobility diameter 30 - 200 nm), with agglomerate silver particles resulting in 5 higher photoelectric yield than unconditioned soot from a propane ame. It is shown for the rst time that the photoelectric yield is signi cantly higher (2.6 ) for fractal-like agglomerate silver particles than sintered, close-packed spherical particles of the same material and mobility-equivalent diameter, which is inferred to be due to the larger material surface area exposed externally to the particle surroundings. It is demonstrated that photoelectric measurements of aerosols re ect the photoelectrically active surface area which depends on the particle morphology and therefore the state of sintering.