EFFECTS ON THE ATMOSPHERE,SOIL AND WATER BODIES

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CHAPTER 4

• EFFECTS ON THE ATMOSPHERE,SOIL AND WATER BODIES

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The Physics of visibility

• visibility of the atmosphere affected from
  several factors
• The optical characteristics of the ilimunation
  source
• Viewed targets
• Intervening atmosphere
• Characteristics of the observer eyesight.

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Contrast

• If the contrast betwen an object and surroundings
  decrease, it becomes difficult to observe the
  object
• The lowest limit of contrast for human observers
  is called threshold contrast and determines the
  maximum distance that we can see objects.

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• Figure 10.1

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Visibility
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Influence of gases and particles on visibility

• Light scattering by gasesous molecules and
  particles
• Light absorption by gases and particles
• DETERMINES THE VISIBILITY
• For instance nitrogen dioxide in the lower
  atmosphere absorbs shorter wavelengths of the
  light,that is why we see redish yellow color in
  polluted atmosphere.
• Carbocaneous nature of particulate matter is
  important regarding absorptive properties of PM.

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• Scattering of light by gaseous molecules and
  particles depends wavelength of the light.
• This process is most responsible for visibility
  degradation.

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The scattering from molecules and very tiny
particles (lt 1 /10 wavelength) is predominantly
Rayleigh scattering. For particle sizes larger
than a wavelength, Mie scattering predominates.
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The blue color of the sky is caused by the
scattering of sunlight off the molecules of the
atmosphere. This scattering, called Rayleigh
scattering, is more effective at short
wavelengths (the blue end of the visible
spectrum). Therefore the light scattered down to
the earth at a large angle with respect to the
direction of the sun's light is predominantly in
the blue end of the spectrum.
Source http//hyperphysics.phy-astr.gsu.edu/hbase
/atmos/blusky.html
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• Mie scattering is not strongly wavelength
  dependent and produces the almost white glare
  around the sun when a lot of particulate material
  is present in the air. It also gives us the the
  white light from mist and fog.

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Light extinction in the atmosphere

• -dIbext I dx
• Where dI decrease in intesity
• bext extinction coefficient (is a
  function of the degree of scattering and
  absorption)
• dx pathlength of light.

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• 10.3-

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• Lv 3.92/bext
• (Lv is the distance at which a black object is
  visible)
• bext brgbagbscatbap
• brg scattering by gaseous molecules(Rayleigh
  scattering)
• bag absorption by NO2 gas
• bscatscattering by particles
• bapabsorption by particles

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10.5
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Scattering and absorption by particles

• 10.7

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Importance of particles

• Particles in the range of 0.1-1 mikrometre
  scatter light very effectively
• Contribution of absorption to extinction
  coefficient is generally less than scattering.
• Characteristics of particulate matter determines
  the scattering properties.

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• Fig10.8

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FORMATION OF ATMOSPHERIC HAZE

• Mist and fog formed condensation of water vapor
  on particulates
• Haze reduced visibility due to fine particles or
  NO2 in the atmosphere.
• Particles must be in the range of 0.1-1
  micrometer.
• The major component of the atmospheric haze is
  the sulfate particulate matter along with Nitrate
  particles. Graphitic material , fine fly ash and
  organic aerosols also makes contribution.