AOSC 200

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AOSC 200

• LESSON 26

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Air Pollution
William Shakespeare 1564-1616, from his play
Hamlet
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Air Pollution
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Air Pollution
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History of Air Pollution

• Air pollution is not a new problem
• In England, wood for burning became scarce, and
  the populace resorted to burning coal which had a
  high sulfur content. The by-products were soot
  (carbon particles) and sulfur dioxide.
• John Evelyn in 1661 wrote about the notorious
  London pea-soup fog. These occur in the fall when
  the Thames is warm but the ground is cold. The
  natural fog this produces is enhanced by the
  extra soot particles, and the sulfur dioxide
  reacts in the water droplets to produce sulfuric
  acid.

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London Killer Smog
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SMOG

• Word coined by Dr. Harold Des Veaux, a London
  physician in 1903.
• SMOKE FOG SMOG
• He meant London smog sulfurous fumes from coal
  burning large water droplets formed around
  smoke particles (soot)
• 1952 Killer smog 4000 deaths. Another episode
  in 1956 led to 1000 deaths.
• Similar events have also occurred in the US.
• Large industrial cities such as St.Louis and
  Pittsburg also suffered from London smog, as
  the use of coal increased.

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PHOTOCHEMICAL SMOG

• In 1940 vegetable crop damage began to be seen in
  the Los Angeles basin. Pine trees began to lose
  their needles.
• Haagen-Smit and colleagues at the University of
  California, Riverside studied this effect using
  smog chambers - large plastic tents into which
  pollutants could be injected and their reactions
  investigated.
• They showed that the effect was due to ozone in
  the atmosphere.
• The ozone was produced by a series of reactions
  involving the oxides of nitrogen and organic
  compounds (e.g. gasoline), both of which are
  emitted by automobiles.
• It is this form of smog that gives the pollution
  seen in the Baltimore/Washington corridor.

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Sources and Types of Air Pollutants

• can be grouped into two categories primary and
  secondary.
• Primary pollutants are emitted directly from
  identifiable sources. They pollute the air
  immediately upon being emitted.
• Secondary pollutants are produced in the
  atmosphere when certain chemical reactions take
  place among primary pollutants.
• Sources. Two types of sources are identified
  fixed sources and mobile sources.

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Composition of the Earths Troposphere
H2
PM
O2
CH4
N2
CO
N2O
O3
?SO2, NO2, CFCs, etc
Ar
Inert gases
CO2
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Denver, Colorado on a clear day
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Denver, Colorado when particulate matter reduced
visibility
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Fine Particles or Particulate Matter (PM)

• PM is made up of suspended particles of either
  solid or liquid pollutants.
• PM is grouped by size under 10 microns is called
  PM10, under 2.5 microns is called PM2.5.

• PM causes increased mortality and morbidity.
• Examples of PM include diesel soot, acids, dust,
  sulfates, nitrates, and organics.

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Formation of the Hydroxyl Radical, OH
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SMOG Chemistry
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Schematic of ozone production from a Volatile
Organic Compound (VOC)
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SMOG

• NEEDS
• Hydrocarbons and nitrogen oxides
• Strong sunlight to start reactions
• Warm temperatures to maintain reactions the
  higher the temperature the faster the rate.
• Peak ozone will be when temperature is highest
  in the afternoon.

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Daily Ozone Cycle
Ozone production follows a daily cycle with
maximum concentrations typically observed in the
late afternoon. This cycle is a signature of the
dynamic processes of atmospheric air pollution
Ozone Concentration
Sunrise
Sunset
Time of day
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Highly Polluted Areas
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Ozone vs NOx for Non Methane HydroCarbon level of
0.6 ppmc
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High Pollution days

• The figure illustrates one of the problems in the
  abatement of pollution. The ozone concentration
  is used as the standard, and yet one can reduce
  the nitrogen oxides by a significant fraction and
  see no change, or even an increase in the ozone
  level.
• Most of the pollution is emitted in the cities,
  which typically puts the atmosphere at the right
  of the figure. As the pollutants move away from
  the city center their concentration gets smaller,
  and the atmosphere is moved toward the left, and
  the ozone increases.
• Hence the suburbs can see more ozone than the
  cities.