Optical Properties

1
Optical Properties
Reading Chap.16
Kuala Lumpur, Malaysia
Glacier NP
Great Smoky Mountain NP
LA, USA
Q Does aerosol have anything to do with the
difference?
2
Definition

• Light visible electromagnetic radiation having a
  wavelength ? between 0.4-0.7 ?m and a frequency f
  between 4-8x1014 Hz.
• cf?
• Index of refraction (refractive index)

(nonabsorbing materials)
(absorbing materials)
m real refractive index
3
Relative index of refraction
Q An example of mr lt 1?
Q What is Kn?
Polarized light when the electric vector
oscillates only in one plane
http//acept.la.asu.edu/PiN/rdg/polarize/polarize.
shtml
4
Extinction
Filtration of photons! Q Important
parameters?

• Bouguers Law

Extinction Efficiency
Q Why can we look at the sun in the evening but
not at noon?
5

• For dp lt 0.05 mm

For dp gt 0.05 mm
For gases,
For dp gt 4 mm, Qe ? 2
(extinction paradox)
Q How does Qe change as dp increases? Q Does a
shorter or a longer wavelength extinct more (same
dp)? Q Why red sky at dawn?
http//www.sciencemadesimple.net/sky_blue.html
6

• Extinction scattering absorption

• Surface area concentration

Diameter of average surface area
?particle diameter by optical response
7

• Mass concentration

Q How does extinction change wrt dp for larger
particles (gt 4 mm)? For smaller particles
(lt 0.05 mm)?
8
ESP, Filtration, now Extinction.. not again!
submicron aerosol!
9
Scattering
Q What is the color of the sky at daytime?
Q Daytime color of the sky if on the moon?
Q Why are they different?
Scattering the re-radiation of the incident
light in different directions
Q Whats the difference between scattering and
absorption? Main cause for black smoke?
Dark cloud?

• Scattering angle
• forward scattering
• backward scattering

? Rayleigh scattering
Q What is the ratio of scattering intensity for
0.02 mm to 0.01 mm? Q Why do we have sky blue?
10
Polarization Components

• Perpendicular to the scattering plane

• Parallel to the scattering plane

Q Angle for max I1? I2?
11
Mie Scattering

• A complete formal solution to Maxwells
  electromagnetic equations for the combined vector
  wave equations for
• the incident wave
• the wave inside the particle
• the scattered wave
• subject to a set of boundary conditions at
  the particle surface.

unpolarized
12
Absorbing particles
Carbon particles with m 2(1-0.33i)
Q Irregular shape/agglomerates?

• For polarized illumination

13
Visibility

• Visual Range (100 300 km for air molecules)

Q If visual range is reported to be 10 km, what
is the main reason? Q What would affect visual
range?

• Inherent contrast

Q What is the minimum of C0? Under what
condition?
Q What is the maximum of C0? Under what
condition?

• Apparent contrast

14

• Koschmieders equation

Q How do we have better contrast?

• Threshold of brightness contrast

Q How do we determine Avogadros Number?
Q What can affect e?

• Visual range (for a dark object)

15
(No Transcript)
16
Optical Measurement

• Optical Particle Counter

http//aerosol.ees.ufl.edu/opc/section01.html
17
Response curve of an OPC

• Advantages
• Can detect very small particles
• Non-intrusive
• Instantaneous and continuous information

• Disadvantages
• too sensitive to small changes in
• refractive index
• scattering angle
• particle size
• particle shape

18
Integrating Nephelometer
Transmissometer Laser Induced Breakdown
Spectroscopy (LIBS) Laser Induced Fluorescenc
(LIF)
19
Summary