Air Pollution

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Air Pollution

• This chapter discusses
• Air pollution types, sources, and trends,
  including tropospheric and stratospheric ozone
• Meteorologic and topographic effects on air
  pollution, as well as pollution in the urban
  environment

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Types Sources of Air Pollution
Primary air pollutants enter the atmosphere
directly, while secondary pollutants form by
chemical reaction. Pollutant sources are both
natural, such as volcanoes and forest fires, and
human caused, such as cars and industry.
Figure 17.1
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Sources of Principal Air Pollutants
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Principal Air Pollutants
Carbon monoxide, sulfur oxides, nitrogen oxides,
volatile organic compounds, and particulate
matter are the most prevalent primary pollutants,
and transportation and power generation are the
primary sources for these pollutants.
Figure 17.2A
Figure 17.2B
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Particulate Matter Pollution
Figure 17.3B
Figure 17.3B
Particulates are classified as having diameters
greater than 10 um and less than 2.5 um. PM-10
pollutants settle out of the atmosphere
relatively quickly compared with the lingering
PM-2.5. Both can adversely affect human health
and reduce visibility.
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Visible Invisible Pollutants
Figure 17.4
Suspended hygroscopic particles may scatter light
and create a white wet-haze, while carbon
monoxide and sulfur dioxide are not visible. The
reaction of nitrogen dioxide and hydrocarbons may
generate unsightly photochemical smog.
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Ozone in the Troposphere
Figure 17.5
Human health is compromised by exposure to ozone
and photochemical smog, which is formed when on a
daily cycle when sunlight dissociates NO2. The
product O reacts with atmospheric O2 to create
O3. Usually, the product NO would then react with
and destroy the 03. Excessive hydrocarbons, often
from automobile exhaust, react with the product
NO and O3 concentrations increase to harmful
levels.
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Tropospheric Ozone Reactions
Ozone production in polluted air when sunlight
hits Nitrogen Dioxide NO2 Solar Radiation
NO O Atomic Oxygen combines w/ Oxygen in
presence of 3rd Molecule O2 O Molecule O3
M Destroy Ozone with Nitric Oxide to form
Nitrogen Dioxide O3 NO NO2 O2 If some
Nitric Oxide reacts with other gases, less Ozone
removed This occurs when certain hydrocarbons
and the hydroxyl radical enter
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Ozone in the Stratosphere
UV radiation has enough energy to adversely
impact the health of plants and animals,
including humans. Naturally occurring O3 in the
stratosphere can block the most harmful UV
radiation from entering the troposphere.
Figure 17.6
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Stratospheric Ozone Reactions
Ozone forms naturally when molecular and atomic
Oxygen combine It forms above 25km and then
drifts downward O2 O Molecule O3
M Ozone is broken into molecular and atomic
Oxygen by absorbing Ultra Violet radiation, or
when two Ozone molecules combine O3 UV O2
O and O3 O3 O2 O2 Natural destructive
gases include Nitric Oxide and Nitrogen
Dioxide NO O3 NO2 O2 and NO2 O NO
O2 A Chlorine gas atom can remove upwards of
100,000 Ozone molecules during their 50 year
lifetime (before removal by other reactions) Cl
O3 ClO O2 and ClO O Cl O2
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Stratospheric Ozone Destruction
Naturally destructive agents of ozone include NO
and NO2, or oxides of nitrogen, which largely
originate from bacterial activity at the earth's
surface. Human released chlorofluorocarbons
(CFCs) have upset the balance of O3 production
and destruction, and have caused formation of
ozone holes and an increase in human UV exposure.
Figure 17.7
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Air Pollution Patterns Trends
Figure 17.8
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Air Pollution Patterns Trends Contd
Air quality in the U.S. may have been at its
worst in the 1970s, but programs implemented by
the Clean Air Act have helped the U.S. move
toward primary ambient air quality
standards. Regional Air Quality Indices may
identify certain non-attainment areas, which are
then targeted by the Environmental Protection
Agency for improvement.
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National Air Quality Standards
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Trends in Tropospheric Ozone
Yearly ozone trends are influenced by hot sunny
weather and light surface winds, but many cities
have demonstrated an overall decline in harmful
ozone levels during the 1980s.
Figure 17.9
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Air Quality Index (AQI)
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Wind Air Pollution
Figure 17.10A
Figure 17.10B
Wind may move along and dilute pollutants through
advection and turbulent mixing, but when winds
slow, the pollutants become more concentrated.
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Pollutants Radiation Inversions
Figure 17.11
Radiation temperature inversions, often lasting
only a few hours at morning with warm air above
cold, creates a stable atmosphere and traps
pollutants at the surface. Pollutant sources
above the inversion will lift beyond the city,
but likely settle down as a pollutant downstream.
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Pollution Subsidence Inversions
Subsidence inversions may last for several days,
which can create major pollution threats by
reducing the mixing depth and layer, forcing a
build-up of unwanted pollutants in the urban
environment.
Figure 17.12
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California's Pacific High
The semi permanent Pacific high promotes
subsiding, and warming, air to settle over the
southern coastal cities and trap pollutants much
of June to October.
Figure 17.13
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Pollutants Topography
Air movement from higher hills to valleys can
strengthen pre-existing surface inversions, as
well as carry pollutants downhill, particularly
in the colder months. Los Angeles and Denver are
two major cities where air pollution is
exacerbated by topography.
Figure 17.15
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Urban and Rural Environmental Conditions
Contrasted
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Pollution in the Urban Environment
Figure 17.16
Human activity and the reduced amount of water
and vegetation in cities creates an urban heat
island, or area of greater temperature than
surrounding country side. The temperature
differential can set up a country breeze, and
bring pollen and rural dust into the city.
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Acid Rain Fog
Atmospheric concentrations of CO2 make rainfall
slightly acidic between 5.0 and 5.6 pH, but power
plant emissions of sulfur and nitrogen oxides
form additional acids that may drop rainfall
acidity from 4.0 to 4.5 in the northeastern U.S.

Figure 17.17
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Impacts of Acid Rain Fog
Figure 17.18
Atmospheric transport of acidic gasses and
condensation nuclei ends when rain droplets
precipitate due to orographic features or fog is
scrubbed by mountaintop trees.
Figure 17.19