AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Charging Fractions of Soot Aggregates
TYLER J. JOHNSON, Robert T. Nishida, Xiao Zhang, Jonathan Symonds, Jason S. Olfert, Adam M Boies, University of Cambridge
Abstract Number: 265 Working Group: Instrumentation and Methods
Abstract Aerosols composed of soot aggregates are common due to the abundance of combustion sources. These particles are often characterized using electrostatic techniques, such as a Differential Mobility Analyzer (DMA), which require the charge fractions of particles to be known. However, previous studies in this area are limited, and all utilized a tandem DMA (TDMA) system. While a few studies have measured the ratios of bipolar charging fractions for aggregates, to the author’s knowledge, Xiao et al. (2012) is the only study to measure absolute charging fractions of aggregates. To overcome challenges of the TDMA charging studies, Johnson et al. (2018) introduced a new method for characterizing charge conditioners with spherical particles using an Aerodynamic Aerosol Classifier (AAC), which exploited the truly monodispersed particle source produced by the AAC at a high transmission efficiency.
This work expands on these previous studies by demonstrating that operating an AAC upstream of a TDMA system can be used to eliminate multiple charging effects in the upstream DMA, while generating a source of non-spherical particles before charge conditioning that is monodisperse in aerodynamic diameter, mobility diameter, and mass, and therefore morphology. Up to 13 charging fractions from a bipolar charge conditioner at seven different mobility diameters (between 79 and 424 nm) of soot aggregates are measured. These results show a higher portion of aggregates become multiply-charged than spherical particles at the same mobility diameter. These results demonstrate the current theory of bipolar charging does not capture the effects of particle morphology.
Bibliography [1] Johnson, T. J., Nishida, R. T., Irwin, M., Symonds, J. P. R., Olfert, J. S., & Boies, A. M. (2018). In International Aerosol Conference (IAC). St. Louis, USA. September 7, 2018. [2] Xiao, K., Swanson, J. J., Pui, D. Y. H., & Kittelson, D. B. (2012). Aerosol Science and Technology, 46(7), 794–803.