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Microscopic Measurement of Particle SizeReading: Chap 20

• Equivalent sizes of Irregular Particles (2-d)– Martin’s diameter:

– Feret’s diameter:

– Projected area diameter:

Q: How do you determine this particle’s size?

Q: Orientation?

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Stage Micrometer (calibration standard printed on glass slide): distance between the smallest lines is 10 mm.

2/0 2n

n dd A-F is 200 times of d0.

Porton Graticule (printed on eye piece)

Calibration

Stratified Counting

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Many aerosol size distributions are skewed, and relatively few large particles are present. Counting a meaningful number of large particles involves counting unnecessarily large numbers of small particles

Field 1Field 2Field 3Field 4Field 5 Q: How to avoid it?

Volume Shape Factor

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3PA

pv d

Equivalent volume diameter

3/1

3

66

vPAe

ep

dd

d

)6/(

Shape factor can also be defined for surface area.

Projected area diameter

Spreading Factor

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0dd

B p

Liquid aerosol particle are spherical when airborne, but they spread out to form a lens-shaped droplet when collected on a glass slideQ: How to reduce the spreading?

Airborne size

On slide

http://www.freepatentsonline.com/6702425-0-large.jpg

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Q: How long is FL’s coastline?

Degussa P25 TiO2 particlesTI 1243

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TurbulenceBorders of clouds and smoke plumesGeometry of lung airways

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Self-similarity at different levels of magnification

fDm kkL 1L: total length: step sizeDf: fractal dimension

For agglomerates,fD

pp

gpp d

RAN

2

Npp: Number of primary particlesRg: radius of gyration (rms average

distance the particle’s mass is from its center of mass)dpp: diameter of primary particles

Fractal Dimension

Q: Df = 1? 2? 3?

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Agglomerates formed by different mechanismsQ: How to change from compact-solid to fluffy? Smoke, Dust and Haze,

Friedlander, 2000

http://en.wikipedia.org/wiki/Diffusion-limited_aggregation

Animation1 Animation2

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Reflection