Modelling Direct Ultraviolet Photoionization and Charge Recombination of Ultrafine Particles

Ultrafine aerosol particles are often purposely charged to enable their detection, capture and control. Charging by direct ultraviolet (UV) photoionization is more efficient than other charging mechanisms such as corona discharge, particularly in size ranges below 50 nm diameter. However, the photoionization behaviour of aerosol ultrafine particles is not well understood. Existing models for photoionization are supplemented with empirically-determined constants which vary for particle size and type. Mechanisms of particle charge recombination with gaseous ions are well understood, but models often neglect or inadequately capture particle and ion wall losses and flow geometry effects. In this work we model the behaviour of UV particle charging and subsequent charge transport and collection in a continuous flow as a means to evaluate photoionization theory and provide tools for quantitative control of ultrafine particle charge states.

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