AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Development of a Real-time Aerosol Mass Distribution Instrument
MODI CHEN, Francisco Romay, Lin Li, Amir Naqwi, Virgil Marple, MSP Corporation
Abstract Number: 530 Working Group: Instrumentation and Methods
Abstract A novel instrument has been developed for real-time aerosol mass distribution measurements. The instrument includes two major components: a relative humidity (RH) conditioner and a 6-stage quartz crystal microbalance (QCM) micro-orifice impactor. The RH conditioner ensures that the incoming aerosol is conditioned to the range of 40 % to 65 % RH. The impactor operates at 10 L/min inlet flow rate and measures the mass of the collected particles in six aerodynamic diameter channels covering the range of 45 nm to 2.5 μm. The nozzles of the impactor stages are clustered so that the particles are collected at the center of the QCM, where the mass sensitivity is known from theory. Laboratory tests conducted with monodisperse aerosol particles showed that the RH conditioning ensured excellent agreement between the mass calculated from direct condensation particle counter (CPC) readings and the mass calculated for the QCM using the Sauerbrey equation. Good agreement was found for mass loadings of up to about 130 μg for solid particles and up to about 2 μg for liquid particles. The agreement also indicated that the RH conditioning eliminated solid particle bounce.
The QCM impactor collection efficiency curves were calibrated with monodisperse liquid particles using conventional calibration techniques. The experimental cutpoints were in good agreement with numerical predictions from classical impactor theory.
The QCM cascade impactor was also tested in an outdoor environment. The measured ambient aerosol distribution was compared with an independent co-located measurement carried out by a wide-range particle spectrometer (WPS). The WPS mobility distribution was converted to the mass distribution assuming the particles were spherical and of 1 g/cm3 density. Good agreement was achieved between the two instruments.