E 10 Smog

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E 10 Smog

• 10.1 State the Source of primary pollutants and
  conditions necessary for the formation of
  photochemical smog

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Aerosols
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Aerosols Big Picture
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Smog

• Smoke and Fog London Smog
• 19th century
• Coal smoke and fog in the city of London
• Industrial smog
• Reducing smog
• Combustion of sulfur containing coal
• Manufacturing and power plants

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Smog

• Consist of water droplets,
• sulfur dioxide/trioxide
• soot
• ash,
• particulates and
• sulfuric acid

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Smog

• Chicago, Beijing
• Cool, cold wet winters
• Thermal inversion trapping pollutants

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Reduction of Smog

• Use of alkaline scrubbers
• Ban on use of coal

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Thermal Inversion

• Gradual decrease in temperature as the altitude
  increases
• Warmer, denser air near the earth surface
• Pollutants produced near the surface of the earth
  move with warm air to the upper atmosphere
• Cooler air takes the place of rising warm air
  near the earth surface

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Thermal Inversion

• Air currents allow the pollutants to be dispersed
• Abnormal temperature arrangement of air masses
  where a layer of warmer air is trapped between
  the two layers of cold air
• Wind gives horizontal movement of air
• Mountains hinders the dispersion
• Flow of cold air creates cool layer

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Thermal Inversion

• No wind, cold temperatures,, mountains
• Warmer air acts as lid

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Thermal Inversion
Normal Condition

Thermal Inversion
altitude
Cooler air
Cold clean air
Warmer air
Polluted cold air
Warmer air
temperature
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E10.2 Outline the formation of

• Secondary Pollutants in Photochemical Smog

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Secondary Pollutants

• Formation of radicals from
• NOx and sunlight
• These radicals and HC
• Leading to the formation of aldehydes and
  peroxyaclynitrates

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Photochemical Smog Follows daily cyclic pattern

• 1.Particulates and un-burnt Hydrocarbon HC act as
  catalyst
• Morning rush hours
• N2 (g) O2 (g) 2 NO(g)
  primary
  pollutant

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2nd Step

• Nitrogen monoxide formed is immediately oxidized
  to nitrogen dioxide
• 2NO (g) O2(g) 2NO2(g)
• NO (g) O3(g) NO2(g) O2(g)

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3rd Step

• Photo-dissociation of nitrogen dioxide in the
  presence of sunlight
• 2NO2(g) UV light
  NO(g) O(g)

Atomic oxygen highly reactive
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4th Step Photo-dissociation

• Atomic oxygen initiates a series of important
  reactions to produce secondary pollutant, ozone
• O(g) O2(g) O3(g)
• Ozone level peaks later in the day
• O(g) H2O(g) 2 OH(g)

Photochemical oxidants
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Continue Step 4

• Atomic oxygen and O3 Photochemical Oxidant
  reactive, toxic
• -capable of oxidizing other substances not easily
  oxidized by O2 under atmospheric conditions ( O2,
  O3 are allotrope)

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Step 4

• HO (g) NO2(g) HNO3(g)
• Formation of nitric acid

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5. Oxidation of HC by O and O3

• Un- burnt hydrocarbon Primary Pollutant
• Produce secondary pollutant aldehyde and
• peroxyacylnitrates(pan)
• lachrymators causes eyes to water
• Disperse in the atmosphere and reach highest
  concentration in the afternoon

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Formation of PAN

• Propagation of free radicals
• RH OH R H2O
• R O2 ROO
• ROO NO2 ROONO2 Termination of
  free radical

Peroxy Free radicals
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Formation of PAN

• R-CO O2 R-C

NO2
R-C
PAN
NO2
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Summary

• Principal source of photochemical smog
• NO, sunlight and hydrocarbons
• Hard to control the pollution of CO, HC and NOx
  by adjusting air to fuel ratio
• CO,HC or NO2

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