Measuring the Charger Efficiency in the Electrical Low Pressure Impactor for Fractal Aggregates Using an Aerodynamic Aerosol Classifier

Nishan Sapkota, Timothy Sipkens, MANG GUAN, Anand Kumar, Steven Rogak, University of British Columbia

     Abstract Number: 438
     Working Group: Instrumentation and Methods

Abstract
The Electrical Low-Pressure Impactor (ELPI) provides a route to rapidly characterize the aerodynamic diameter of particles. However, its operating principle involves unipolar charging of the aerosol. The charging efficiency of this unipolar charger is defined as a power-law function of electrical mobility diameter and is well known for spherical particles. However, for low density fractal aggregates, such as soot, the charging-equivalent diameter is larger than the mobility diameter and much larger than the aerodynamic diameter, complicating analysis. Previous attempts to address this issue involved measuring charging efficiency using mobility-classified particles.

The recent introduction of the Aerodynamic Aerosol Classifier (AAC) has provided another route to characterize the aerodynamic diameter of the particles that avoids the effects of multiply-charged particles at the cost of response time. Here, we use the AAC to determine the charging efficiency in the ELPI. Combining this arrangement with a Scanning Mobility Particle Spectrometer (SMPS), this setup can be used to measure the charging behavior as a function of both the aerodynamic and mobility diameters. Further, this setup allows for the transfer of the accuracy of the AAC to a rapid response instrument in the ELPI, which can then be used for accurate, real time measurement of soot. Results of the method are presented for both spherical particles and soot from an Argonaut inverted burner.