Optical Properties of Soot Particles as Function of Relative Humidity

  • Author / Creator
    Zhao, Boyang
  • Optical properties, i.e. scattering coefficient and absorption coefficient, of soot aerosol particles were investigated as they restructure during a simulated atmospheric ageing process. The soot particles were generated by a McKenna burner and injected into a smog chamber after being denuded and size selected. In the smog chamber, the soot restructuring process was induced by formation of a secondary organic aerosol (SOA) coating, which was generated by the photo-oxidation reaction of the SOA precursor p-xylene with OH radical. The particle diameter, mass, scattering and absorption coefficients were monitored with a scanning mobility particle sizer, a centrifugal particle mass analyzer, and a photoacoustic extinctiometer, respectively. Effective density and shape factor for the particles were determined to assess the degree of restructuring. Experiments were done at different relative humidities (RH) and I found that higher RH leads to a faster restructuring process. Mass scattering cross-section, mass absorption cross-section, and mass absorption cross-section with respect to bare soot particles were calculated to show how scattering and absorption are affected by the restructuring process. Under all RH conditions, the mass scattering cross-section increased for both coated and denuded soot particles. The mass absorption cross-section with respect to bare soot particle shows an increasing trend for coated soot particles as the mass growth factor increases. High and low RH conditions give rise to a higher value of mass absorption cross-section with respect to bare soot particles compared to intermediate RH conditions (RH=40%). The mass absorption cross-section value with respect to bare soot particles for intermediate RH is about 30% less than those for low and high RH. The overall work can provide optical information to the process of soot particles restructuring induced by SOA coating under different RH conditions.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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