AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
A Real-time Impactor for Ambient and Vehicle Exhaust Particle Mass Distribution Measurement
Yue Lin, Liem Pham, Heejung Jung, MODI CHEN, Francisco Romay, University of California, Riverside
Abstract Number: 778 Working Group: Instrumentation and Methods
Abstract A real-time cascade impactor based on quartz crystal microbalance (QCM) was developed for measuring aerosol mass distribution. This instrument contains two key components: an RH conditioner that conditions particles in the 45% to 65% relative humidity range to ensure reliable mass sensing, and a cascade impactor with QCM sensors to measure the mass of particles between 45 nm and 2.5 μm aerodynamic diameter.
In this study, the real-time impactor was compared with the Fast Mobility Particle Sizer Spectrometer (FMPS) and the Scanning Mobility Particle Sizer Spectrometer (SMPS) during simultaneous measurements of ambient particles at the South Coast Air Basin. These instruments were tested with aerosols from urban background, on-road and roadside environments. The urban background aerosol measurement was conducted at the UC Riverside campus. The ambient particles without thermal conditioning were sampled for 12 hours. In another 17-hour experiment particles were thermally treated with a Catalytic Stripper working at 300°C to remove the semi-volatile particle fraction upstream of the sampling instruments. An aerosol chamber was installed at the inlet of the instruments to smooth particle size and mass variation. The SMPS data was collected simultaneously with the real-time impactor and the FMPS data. The roadside measurement with the real-time impactor and the FMPS was conducted for 2 hours at the downwind side of Freeway I-215 during afternoon traffic hours. On-road measurements with the impactor and the FMPS were conducted on a round-trip from UC Riverside to Yorba Linda taking State Freeway 91. Preliminary analysis indicates that the real-time impactor could track ambient aerosol mass evolution closely when compared with the FMPS. The mass distribution of real-time impactor also agrees well with that calculated from FMPS for the various size distributions when using a proper particle density for the FMPS mas distribution calculation. The real-time impactor is stable and reacts sensitively to relatively fast-changing roadside aerosol concentrations. In addition time resolved mass distribution was compared between QCM and AVL MSS (Micro Soot Sensor). QCM showed mass distribution as well as desorption of semivolatile PM during the transient test cycle.