Journal
AEROSOL SCIENCE AND TECHNOLOGY
Volume 53, Issue 12, Pages 1429-1440Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/02786826.2019.1661958
Keywords
Hans Moosmuller
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Funding
- Alphasense Ltd., Cambridge Trust
- Natural Sciences and Engineering Research Council of Canada (NSERC)
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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 5x higher photoelectric yield than unconditioned soot from a propane flame. It is shown for the first time that the photoelectric yield is significantly higher (2.6x) 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 (c) 2019 American Association for Aerosol Research
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