An atmospheric pressure plasma afterglow to charge ultrafine aerosol particles

A novel flowing plasma system aimed at increasing charging efficiency of particulate matter and effective removal through electrostatic precipitation is studied. Nanoparticles are passed through the spatial afterglow of an atmospheric pressure radio-frequency glow discharge plasma. Particle charging efficiencies and polarities are measured at different plasma-aerosol gaps, aerosol and plasma flow rates, plasma powers, and afterglow DC bias. Various timescales are calculated to explain the transport of charge carriers that facilitate particle charging processes. The experimental results showed increased charging efficiency and net positive charging at longer gaps between the afterglow and aerosol stream and lower aerosol flow rates. Timescale analysis indicates that when ample residence time is provided, transport of charge carriers shifts from ambi-polar diffusion to free diffusion, and electrons are rapidly lost from the afterglow, resulting in highly efficient, net positive charging of particles. The charging efficiency of particles in optimized operating conditions was comparable or higher than reported collection efficiencies of electrostatic precipitators. The findings overall demonstrate that glow discharges are capable of charging particles not immersed in the plasma bulk, and such systems show promise for improving performance of particle mitigation technology.