Presentation Slides for Atmospheric Pollution: History, Science, and Regulation Chapter 7: Effects of Pollution on Visibility, Ultraviolet Radiation, and Atmospheric Optics

By Mark Z. Jacobson Cambridge University Press, 399 pp. (2002)

Last update: March 23, 2005 The photographs shown here appear in the textbook and are provided to facilitate their display during course instruction. Permissions for publication of photographs must be requested from individual copyright holders. The source of each photograph is given below the figure and in the back of the textbook.

Sir Isaac Newton (1642-1727)

Edgar Fahs Smith Collection U. Penn. Library White light passing through a prism separates into a variety of colors called the light spectrum .

Primary colors: Blue (0.38-0.5 m m) Green (0.5-0.6 m m) Red (0.6-0.75 m m) Human vision peaks at 0.55 m m Colors additive Red+green = yellow

Light Attenuation Processes

Gas absorption Gas scattering Aerosol and hydrometeor particle absorption Aerosol and hydrometeor particle scattering Reflection Refraction Dispersion Diffraction

Gas Absorption

Conversion of radiative energy to internal energy by a gas molecule, increasing the temperature of the molecule Attenuation of light intensity 

I

=

I

0 e s

a,g,q

(

x

-

x

0) (7.2) Absorption extinction coefficient  s

a,g,q

=

N q b a,g,q

(7.1)   = gas absorption cross section

N

= gas concentration Figure 7.2

Light-Absorbing Gases

Gas Absorption wavelengths ( m m) Visible/Near-UV/Far-UV absorbers Ozone < 0.35, 0.45-0.75

Nitrate radical Nitrogen dioxide < 0.67

< 0.71

Near-UV/Far-UV absorbers Formaldehyde Nitric acid < 0.36

< 0.33

Far-UV absorbers Molecular oxygen Carbon dioxide Water vapor Molecular nitrogen < 0.245

< 0.21

< 0.21

< 0.1

Absorption Extinction Coefficients of Nitrogen Dioxide and Ozone

10 1 10 0 10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 NO 2 (g) (0.25 ppmv) NO 2 (g) (0.01 ppmv) O 3 (g) (0.25 ppmv) O 3 (g) (0.01 ppmv) 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7

Wavelength ( m m) Figure 7.3

Gas (Rayleigh) Scattering

Redirection of radiation by a gas molecule without a net transfer of energy to the molecule Probability distribution of where a gas molecule scatters incoming light Figure 7.4

Lord Baron Rayleigh (John William Strutt) (1842-1919)

American Inst. of Physics Emilio Segrè Visual Archives, Physics Today Collection

Color of the Sky and Sun

Figure 7.6

Yellow Sun at Sunset M.Z. Jacobson

Red Horizon Over Clouds During Sunset

Mark Z. Jacobson

Particle Absorption

Conversion of radiative energy to internal energy by a particle, increasing the temperature of the particle Attenuation of light through particle 

I

=

I

0 e -4  (

x

-

x

0)/  (7.4)  = imaginary refractive index  = wavelength Figure 7.9

Substance Liquid water Black carbon Organic matter Sulfuric acid

Refractive Indices

<- Real 1.34

1.82

1.45

1.43

0.5 m m --> Imaginary 1x10 -9 0.74

0.001

1x10 -8 <- Real 1.22

2.4

1.77

1.89

10 m m --> Imaginary 0.05

1.0

0.12

0.46

Table 7.2

Transmission of Light Through Black Carbon and Water Particles

Diameter ( m m) 0.1

1.0

10 <-- Transmission (

I

/

I

0 ) --> Black carbon (  =0.74) ( Water  =1x10 -9 ) 0.16

0.999999997

8x10 -9 0 0.99999997

0.9999997

Table 7.2

Imaginary Refractive Indices of Some Liquid Organics

4-nitrophenol anion 4-nitrophenol 1 2-nitrophenol 0.1

0.01

0.001

0.25

2-hydroxybenzaldehyde 0.3

0.35

0.4

3-nitrophenol Wavelength ( m m) 0.45

0.5

Figure 7.10

Effects of Pollution on UV Radiation Reaching Surface

60 50 40 30 20 10 0 0 M t. Wilson Central L. A.

Claremont Riverside UV 295 -385 nm 8 16 24 32 Hour after first midnight 40 48 Figure 7.11

Particle Scattering

Reflection The bounceoff of light from an object at the angle of incidence Refraction Bending of light as it travels between media of different density Dispersion Separation of white light into colors Diffraction Bending of light around objects Scattering Combination of reflection, refraction, dispersion, diffraction.

The deflection of light in random directions.

Reflection and Refraction

Snell’s Law 

n

2 /

n

1 = sin  1 /sin  2 (7.5) Real part of refractive index 

n

1 =

c

/

c

1 (7.6)

c

= speed of light in vacuum Figure 7.12

Refraction of Starlight

Apparent position Actual position Atmosphere Earth Figure 7.13

Diffraction Around A Particle

Huygens' principle Each point of an advancing wavefront may be considered the source of a new series of secondary waves Figure 7.14

Radiation Scattering by a Sphere

Ray A is reflected Ray B is refracted twice Ray C is diffracted Ray D is refracted, reflected twice, then refracted Ray E is refracted, reflected once, and refracted Figure 7.15

Forward Scattering of Sunlight

Mark Z. Jacobson

Primary Rainbow

Commander John Bortniak, NOAA Corps, available from the National Oceanic and Atmospheric Administration Central Library

Geometry of a Primary Rainbow

Figure 7.18

Soot Absorption/Scattering Efficiencies

Single Particle Absorption/Scattering Efficiency at  = 0.50 m m 2 2 M ie regime Geometric regime 1.5

Q s

1.5

1 1

Q a

0.5

0.5

Q f

0 0.01

0.1

1 10 Particle diameter ( m m) 100 0 1000 Fig. 7.19

Water Absorption/Scattering Efficiencies

Single Particle Absorption/Scattering Efficiency at  = 0.50 m m.

5 4 3 2 1 0 0.01

Q s

0.1

M ie regime

Q

1

f

10 Geometric regime

Q a

Particle diameter ( m m) 100 10 3 10 1 10 -1 10 -3 10 -5 10 -7 10 -9 1000 Figure 7.20

Visibility Definitions

Meteorological range Distance from an ideal dark object at which the object has a 0.02 liminal contrast ratio against a white background Liminal contrast ratio Lowest visually perceptible brightness contrast a person can see Visual range Actual distance at which a person can discern an ideal dark object against the horizon sky Prevailing visibility Greatest visual range a person can see along 50 percent or more of the horizon circle (360 o ), but not necessarily in continuous sectors around the circle.

Visibility

The intensity of radiation increases from 0 at point

x

0 to

I

at point due to the scattering of background light into the viewer’s path

x

Figure 7.21

Meteorological Range

Change in object intensity along path of radiation d

I

d

x

Total extinction coefficient  s

t



I B



I

 s

t

 s

a

,

g

 s

s

,

g

 s

a

,

p

 s

s

,

p

(7.9) (7.10) Integrate (7.9)

I B



I B I



e

s

t x

(7.11) Define liminal contrast ratio --> meteorological range (7.12)

C ratio



I B I B



I

 0.02



x

 3.912

s

t

Meteorological Range

Polluted day Less polluted day Gas scattering Meteorological Range (km) Gas absorption Particle scattering Particle absorption 366 130 9.59

49.7

352 326 151 421 All 7.42

67.1

(Larson et al., 1984) Table 7.4

Meteorological Range Due to Gas Scattering and Absorption

Wavelength Rayleigh Scat.

( m m) 0.42

0.50

0.55

0.65

(km) 112 227 334 664 <-- NO 2 (g) absorption --> 0.01 ppmv (km) 296 641 1,590 13,000 0.25 ppmv (km) 11.8

25.6

63.6

520 Table 7.3

Winter and Summer Maps of Light Extinction

Schichtel et al. (2001)

Los Angeles Haze

Gene Daniels, U.S. EPA, May, 1972, Still Pictures Branch, U.S. National Archives

Haze and Fog Over Los Angeles

Gene Daniels, U.S. EPA, May, 1972, Still Pictures Branch, U.S. National Archives

Brown Color of Nitrogen Dioxide

From preferential

transmission

makes brown)

absorption

of blue and some green and of red and remaining green (which Visible Infrared

Black Color of Soot

Soot appears black because it

transmits absorbs

no light.

all visible wavelengths (blue, green, red) and Visible Infrared

Colors in Los Angeles Smog (Dec. 2000)

Mark Z. Jacobson

Red Sky Due to Smog (Salton Sea, California)

Charles O'Rear, U.S. EPA, May, 1972, Still Pictures Branch, U.S. National Archives

Purple Sky After El Chichon Volcano, 1982

J. Lew