10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Development of Caltech Scanning-mode Nano Radial Differential Mobility Analyzer System and Its Application to Nucleation Study at the CLOUD Experiment
CHANGHYUK KIM, Huajun Mai, Wilton Mui, Stavros Amanatidis, Dominik Stolzenburg, Richard Flagan, CLOUD Collaboration, California Institute of Technology
Abstract Number: 1419 Working Group: Instrumentation
Abstract Size distributions of particles can be measured by classifying the particles using the electrical mobility and detecting the number concentration of the classified particles using a condensation particle counter (CPC). However, low charging efficiency and high diffusion loss make it challenging to apply this method for particles smaller than 10 nm. Moreover, diffusion broadening reduces the resolution of electrical mobility methods when particles are classified at low voltages. For this reason, previous efforts have employed high sheath flow rates to achieve high resolution, but this has required impractically high flow rates.
The Caltech nano radial differential mobility analyzer (nRDMA) was designed to enable for classifying particles as small as 1 nm in diameter, the size range of fresh nuclei, with high resolution and compact size, but maintaining the sheath flow rates similar to those used in common DMAs. This instrument enables scanning-mode measurements of the size distribution of sub-10 nm particles with a time resolution of 2 minutes by combining the nRDMA with a non-diffusion resolving power of 10 (1.2 and 12 L/min for the aerosol and sheath flow rates, respectively) with a custom-made two-stage condensation particle counter detector. The two-stage detector was designed to grow the size of sub-10 nm particles over 100 nm by condensing diethylene glycol, and then detect them by a commercial TSI butanol CPC (3760A, d50 = 10 nm). A new, low particle-loss soft-x-ray charge conditioner was also developed to produce a well-constrained, steady-state charge distribution on the sub-10 nm particles.
This nRDMA system has been deployed in studies of the nucleation and growth kinetics of particles in the CLOUD (Cosmics Leaving Outdoor Droplets) Experiment at CERN. The relatively high resolution enables quantitative analysis of early-stage growth rates (GRs) from the measured size distribution of incipient particles formed in the CLOUD chamber. The growth rate has been calculated from the 50% appearance time at each size channel. The calculated growth rates agree well with those obtained by other aerosol instruments of the CLOUD collaboration, which proved the reliability of this nRDMA system.