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Direct ultraviolet photoionization electrically charges particles using a mechanism distinct from diffusion 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 classified using an aerodynamic aerosol classifier (AAC) and subsequently measured with a scanning mobility particle sizer (SMPS) and photoionization measurement system in parallel. This configuration allows direct comparison of photo-emission from high concentrations of initially neutral, monodisperse aerosols with different 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 flame. It is shown for the first time that the photoelectric yield is significantly 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 reflect the photoelectrically active surface area which depends on the particle morphology and therefore the state of sintering. Copyright © 2019 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Planar two-dimensional two-color time-resolved laser-induced incandescence (2D-2C-TiRe-LII) is employed to investigate soot formation in a standard ethylene laminar diffusion flame. The time resolution of the 2D LII signal is realized by shifting the delay time of ICCD cameras. The two-color configuration is applied to measure the peak temperatureof soot particles immediately after the laser pulse rather than using the energy balance to compute. The Sauter mean diameterD32and the corresponding distribution width parameter σ of the measured soot particles is extracted by using an error minimization method. The method shows that a range of possible geometry mean particle diameters and corresponding distribution width parameters are also possible solutions, and further information on realizable particle size distribution widths is necessary to narrow down the extracted diameter. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]