AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Soot Aggregate Restructuring: Effect of Surface Chemistry and Water Condensation
XIAOFEI MA, Christopher Zangmeister, George Mulholland, Michael Zachariah, University of Maryland-College Park
Abstract Number: 103 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract A collapsed soot structure is observed in laboratory prepared fresh soot particles upon exposure to high humidity environment followed by rapid water evaporation. The fresh soot was generated in a Santoro style ethylene diffusion burner, and the condensation of water on soot particles was realized in a temperature-controlled ADI water growth tube. The structure transformation of soot particles under different humidity conditions was monitored using a Differential Mobility Analyzer – Aerosol Particle Mass Analyzer (DMA-APM) and Tandem Differential Mobility Analyzer (TDMA) methods. The primary measured properties were mass-mobility scaling exponent, particle mass and mobility size before and after processing. A critical saturation ratio was observed above which the structure of soot start to collapse. The morphological change was visualized by taking electron microscopic images. The effect of soot surface properties on the soot structure change was investigated by measuring the critical saturation ratio for different surface-modified soot. XPS analysis found the critical saturation ratio was related to the soot oxygenation extent. A mechanism based on water droplet formation and capillary force on soot primary particles was proposed to explain the soot structure collapse process.