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Abstract
Soot particles in the atmosphere can be coated with organic or nonorganic material, which may affect particle morphology and optical properties. The effect of the mass of coating on the morphology of soot particles was studied using oleic acid and dioctyl sebacate (DOS) coatings. A wide range of coatings were used, with up to 10 times as much coating as the mass of the soot. It is shown that as the coating mass increases the degree of collapsing increases until the coating is so large that the soot particle becomes completely contained within a spherical droplet of the coating material. Higher amounts of coating will not cause further collapse of the particle. The degree of collapse is also a function of the initial size of the soot particle but was independent of the coating materials tested, which have similar surface tensions. A model is presented to predict the change in mobility diameter as a function of coating mass ratio. The effect of coating mass on effective density, shape factor, and fractal dimension is also reported.
Copyright 2013 American Association for Aerosol Research
Acknowledgments
The authors would like to acknowledge the support of NSERC Discovery Grant and Brookhaven National Laboratory (Grant number: SFR02855).
Notes
An inversion of the data was not performed to find the size distribution of the particles in these cases due to the inversion errors associated with narrow transfer functions entering the second DMA (Rader and McMurry Citation1986).
Previous work has erroneous called this exponent the “fractal dimension” or “mass fractal dimension.” The mass-mobility exponent is not equivalent to the fractal dimension and the term “mass fractal dimension” is a misnomer. Sorensen (2011) has shown the relationship between the true fractal dimension and the mass-mobility exponent.