Abstract Number: 739 Working Group: Instrumentation and Methods
Abstract A laminar flow particle size magnifier (PSM) was developed and coupled to a condensation particle counter (CPC) to detect aerosol particles in less than 10 nm particle diameter range. The performance of the PSM-CPC system (called “the system”) was evaluated using a diethylene glycol (DEG) and dimethyl phthalate (DMP). False counts rates induced by homogeneous nucleation of working fluid (WF) vapor were evaluated as a function of saturator temperature. The false count rate (FCR) of DEG based system is significantly affected by water-vapor in a sample flow indicating that binary homogeneous nucleation between DEG and water vapor induces false counts. Whereas FCR of DMP-based system is minimally affected by water vapor in a sample flow indicating that false counts remain stable regardless of the variation in the relative humidity of sampled aerosol. Detection efficiencies of the system were evaluated using negatively charged NaCl and Ag aerosol over 1.0 to 10 nm particle diameter range. The efficiency curve of DEG-based system had higher plateau value (=0.93) than DMP-based system did (=0.84). The value of d50, which is the particle diameter at 50% detection efficiency, showed that d50 of DMP-based system are less dependent on particle material than DEG-based system are. DEG-based system detects less than 1 nm NaCl particles, and the observed trend is most likely related to that bulk NaCl crystals dissolves in DEG liquid.