Soot Particle Mass and Fractal Dimension

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Apparatus for Soot Production, Processing, and
Analysis
Reactant
AMS Aerosol Mass Spectrometer
Exhaust
Isokinetic Sampler
DMA Differential Mobility Analyzer
N2
Reaction Zone
Movable Injector
Soot particles produced by combustion
CCN Cloud Condensation Nucleus Counter
SMPS Scanning Mobility Particle Sizer
DMA Differential Mobility Analyzer
CPC Condensation Particle Counter
N2 O2 Propane
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Soot Particle Mass and Fractal Dimension
dm 350 nm
Increased propane/O2 ?
Particles are more spherical and have more mass
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Soot Fractional Composition

• Increase in fractional PAH content
• ? Decrease in fractional BC content

Increase in propane/O2
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Relationship of Deposited Anthracene Mass to
Temperature (dm)i 250 nm
Soot particles are coated with anthracene
Coated particles are heated to remove anthracene
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Effect of Anthracene Coating on Particle Shape
(dm)i 250 nm
? 1 for sphere
Type 1 soot particles become near-spherical with
coating.
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Type 2 (Near-Spherical) Particles Heated to
Remove Flame-Generated PAHs
Type 2 particles do not become fractal when PAH
coating is removed.
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Formation of Type 2 Soot
PAHs condense on agglomerate forming
near-spherical type 2 soot.
BC spherules form fractal agglomerate. PAHs
remain in vapor phase.
PAHs
Black Carbon Spherules
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Ambient Particles Compared to Laboratory Soot
As the particles age further, the small particle
mode disappears
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T
The Benjamin Y.H. Liu Award AAAR Douglas R.
Worsnop and John T. Jayne Aerodyne Research,
Inc.
Their mass spectrometer system (AMS) with
molecular beam, aerosol focusing, and thermal
vaporization have created a paradigm shift in
online, size-resolved atmospheric aerosol
composition. The supporting letters all
highlighted their dedication to supporting the
many AMS users to do the best science possible
with the instrument.
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Measurements and Calculated Properties
Experimental Measurements Mobility Diameter
(dm) Vacuum Aerodynamic Diameter
(dva) Non-Refractory Composition (PAH and
aliphatic mass)
Calculated Properties Total Particle Mass (mp)
and Black Carbon Mass (mBC) Particle Density
(?p) Particle Volume (V) Volume Equivalent
Diameter (dve) Dynamic Shape Factor (?)
? Drag on particle / Drag on sphere with
diameter dve Fractal Dimension (Df)
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Estimation of Black Carbon Content, Particle
Density, and Dynamic Shape Factor
Assumptions

• No internal voids
• 2. Dynamic shape factor is the same in continuum
  and free-molecular regimes
• 3. BC, PAH, aliphatic species are immiscible
• 4. Component densities estimated (?BC 2.0 g/cc,
  ?PAH 1.3 g/cc, ?AL 0.85 g/cc)

System of equations relating equivalent diameter
and mass
The system is underdetermined (3 equations, 4
unknowns dve, ?p, ?, mBC). However, using
assumptions 3 and 4, ?p may be expressed as
The system has been reduced to 3 equations with 3
unknowns, and can be solved for mBC, ?p, and??.