Abstract Number: 594 Working Group: Instrumentation and Methods
Abstract A technique for making the particle number concentration standard liquid suspension is being developed at AIST, Japan. The size-standard polystyrene latex (PSL) spheres are first aerosolized by atomizing the liquid suspension. A differential mobility classifier extracts the PSL spheres from the generated aerosol. About a half of the classified aerosol is sampled into a condensation or an optical particle counter to measure the concentration of the PSL spheres, and another half is send to a growth tube collector (GTC). Inside the GTC the PSL spheres become seeds for the condensational growth and become micrometer-sized water droplets. These PSL-seeded water droplets are accelerated by properly designed nozzles and impacted onto a liquid surface contained in a small vial. A liquid-borne particle counter (LOPC) was used to obtain the total number of PSL spheres collected and stably suspended inside the liquid. The total number of PSL-seeded water droplets produced is known from the measurements in the aerosol phase; therefore, we can evaluate what fraction of these particles became stably suspended particles in the liquid phase. Since the LOPC cannot accurately measure the particle number concentration below several hundred nanometer, the proposed method was evaluated by using the PSL spheres between 250-1000 nm. Above 90% of the condensationally grown PSL spheres became stable liquid suspension, and the performance was reproducible and had no significant size dependence. The proposed method was first verified using a miniature GTC which has a sampling flowrate at 0.3 L/min. The method could be successfully scaled up by 10 times by using a 3.0 L/min GTC. Since the previous studies has proven that the activation efficiency and the final droplet size of the GTC is constant over the particle diameter above 10 nm, the proposed method can potentially make a number concentration standard suspension down to this size range.