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Environmental Science
A Study of Interrelationships
Tenth Edition
Enger • Smith
Chapter 17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Air Quality Issues
Chapter 17
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Outline
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The Atmosphere
Categories of Air Pollutants
Control of Air Pollutants
Acid Deposition
Ozone Depletion
Global Warming and Climate Change
Addressing Climate Change
Indoor Air Pollution
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The Atmosphere
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The atmosphere is composed of 78.1% N,
20.9% O and about 1% of other gases such
as argon, carbon dioxide, methane, and
water vapor.
– Most of the atmosphere is held close to
the earth by the pull of gravitational force,
thus it gets thinner with increasing
distance from the earth.
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The Atmosphere
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Troposphere extends from the earth’s
surface to about 10 km above the earth.
Stratosphere extends from the top of the
troposphere to about 50 km above the earth.
– Most ozone located in a band between 15
and 30 km.
Mesosphere extends from 50-80 km above
the earth.
Thermosphere extends to about 300 km
above the earth.
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The Atmosphere
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The Atmosphere
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As the atmosphere absorbs heat from the
earth, it expands and rises.
– When heat is radiated into space, air
cools, becomes more dense, and flows
toward the earth.
Air quality degraded by multiple sources.
– Air pollution includes both aesthetic and
human health problems.
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Air Pollution and Population Centers
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The Atmosphere
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Many of the mega cities of the developing
world have extremely poor air quality.
– Increases death rate and lowers general
health of the population.
 Chronic coughing and susceptibility to
infections are common.
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Categories of Air Pollutants
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Primary Air Pollutants
– Five major materials released directly into
the atmosphere in unmodified forms.
 Secondary air pollutants form under
reaction of primary pollutants and water
or sunlight.
– Criteria Air Pollutants are those pollutants
for which specific air quality standards
have been set.
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Primary Air Pollutants
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Carbon Monoxide - Produced when organic
materials are incompletely burned.
– Single largest source is the automobile.
– Not a persistent pollutant.
– Binds to hemoglobin in blood and makes
the hemoglobin less able to carry oxygen.
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Carbon Monoxide
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Most dangerous in enclosed spaces.
– Cigarette smoking an important source.
 U.S. levels have decreased by about
21% between 1993 and 2003.
 Increasing number of cars on the
road and miles driven, can offset
savings from catalytic converters.
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Primary Air Pollutants
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Particulate Matter - Minute pieces of solid
materials (< 10 microns) dispersed into the
atmosphere.
– PM10 and PM 2.5
 Larger than 2.5 microns are primary
pollutants; Smaller than 2.5 are mostly
secondary pollutants.
 Can accumulate in lungs and interfere
with the ability of lungs to exchange
gases.
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Particulate Matter
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Amount of PM10 has decreased 9% between
1996 and 2002.
– U.S. EPA has been setting PM2.5 standards
for a shorter period of time.
 Amount decreased 7% between 1996
and 2002.
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Primary Air Pollutants
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Sulfur Dioxide (SO2) - Sulfur and oxygen
compound produced when sulfur-containing
fossil fuels are burned.
– Burning coal releases SO2.
 Today over 65% of SO2 released into the
atmosphere is primarily from coal-burning
power plants.
 U.S. levels of SO2 decreased 30%
between 1993 and 2002.
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Primary Air Pollutants
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Nitrogen Dioxide
– Oxides of Nitrogen (NOx) - Formed when
combustion takes place in the air.
 N and O molecules from the air may react
with one another.
 Nitrogen Monoxide NO
 Nitrogen Dioxide NO2
 Automobile engine is primary source.
 U.S. levels decreased 10% between
1993 and 2002.
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Primary Air Pollutants
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Lead
– Lead (Pb) can enter the body through
breathing airborne particles or consuming
lead deposited on surfaces.
 Leaded gasoline was primary source.
 North American lead levels fell 94%
between 1982 and 2002.
 Currently, about 80% of gasoline sold
in the world is unleaded.
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Lead Emissions
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Primary Air Pollutants
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Volatile Organic Compounds
– Hydrocarbons - Group of organic
compounds consisting of carbon and
hydrogen.
 Evaporated from automobile fuel or
remnants of fuel incompletely burned.
 Catalytic converters used to burn
exhaust gases more completely.
 U.S. levels decreased 25% between
1993 and 2002.
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Ground-Level Ozone
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Ozone (O3) is a molecule of three oxygen
atoms bonded to one another.
– Extremely reactive secondary pollutant.
 Permanent Lung Damage
 Damages Plants
 Destroys Chlorophyll
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Photochemical Smog
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A mixture of primary and secondary
pollutants. Forms when primary pollutants
interact under the influence of sunlight.
– Two most destructive components:
 Ozone
 Peroxyacetyl Nitrates
– Large cities ringed by mountains tend to
have trouble with photochemical smog.
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Daily Changes in Photochemical Smog
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Photochemical Smog
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Thermal Inversions - Warm air becomes
sandwiched between two layers of cold air
and acts like a lid on the valley.
– Warm air cannot rise, causing smog
accumulation.
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Thermal Inversion
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Hazardous Air Pollutants
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Hazardous Air Pollutants (HAP) or Air Toxics
are compounds that can harm human health
or damage the environment.
– Some released from consumer activities:
 Benzene escapes during automobile
refueling.
– Majority released from manufacturing:
 Perchloroethylene released from dry
cleaning processes.
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Control of Air Pollution
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Motor Vehicle Emissions
– U.S. regulations have pressured the
automobile industry to reduce emissions.
 Positive Crankcase Ventilation Valve
(PCV)
 Air Pollution Control Valves (APC)
 Catalytic Converters
 Lead-Free Fuel
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Control of Air Pollution
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Particulate Matter Emissions
– Industrial Activities
 Mining
– Improper Land Use
 Overgrazing
– Fossil Fuel Burning
 Diesel Fuel
– Personal Activities
 Fireplaces and Wood-Burning Stoves
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Control of Air Pollution
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Power Plant Emissions
– Sulfur Removal
 Switch to low-sulfur fuel.
 Remove sulfur from fuel before use.
 Scrubbing gases emitted from
smokestack.
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The Clean Air Act
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Clean Air Act
– Series of detailed control requirements
the federal government implements and
states administer.
 Emissions of six worst air pollutants
dropped 48% from 1973 to 2002,
despite an increase in energy
consumption of 42%.
 EPA estimates benefits have
outweighed costs 40 to 1.
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Acid Deposition
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Acid Deposition is the accumulation of
potential acid-forming particles on a surface.
– Sulfur Dioxide and Nitrogen oxides are
carried aloft by wind and form secondary
pollutants (acids), and then are carried
back to earth in wet (snow, rain, fog) and
dry (particulate) form.
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Sources of Acid Deposition
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Acid Deposition - Harmful Effects
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Property / Structural Damage
– Limestone Degradation
Foliage Damage
– Acidic Soil - Reduced Nutrient Absorption
Weakened Plant Defenses
– Stressors
Lake Acidification
 Food Chain Disruption
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Ozone Depletion
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Ozone is formed in the stratosphere when
high energy ultraviolet radiation splits
diatomic oxygen into atomic oxygen.
– The atomic oxygen may then combine
with another diatomic oxygen molecule to
form triatomic oxygen (Ozone - O3).
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Ozone Depletion
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In the 1970’s, it was discovered that CFCs
were lowering the average concentration of
ozone in the stratosphere.
– CFCs take 10-20 years to make it into the
stratosphere.
 Can react with ozone for up to 120
years.
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Ozone Depletion
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In the stratosphere, UV radiation breaks
down CFC molecules, releasing atomic
chlorine. A free chlorine atom reacts with an
ozone molecule, converting it from O3 to O2.
– Montreal Protocol (1987).
 Several industrialized countries agreed
to reduce CFC production by 50% by
2000.
 As a result, emissions dropped 87%
from their peak in 1988.
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Global Warming and Climate Change
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Climatic records indicate over past 160,000
years, a correlation between greenhouse gas
concentration and global temperatures.
UN established Intergovernmental Panel on
Climate Change (IPCC)
– 1996 Assessment - Concluded climate
change is occurring and it is highly probable
human activity is importance cause of the
change.
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Global Warming and Climate Change
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IPCC Conclusions
– Average temperature of the earth increased
.5 to 1.0 degrees Fahrenheit over the last
100 years.
– Strong correlation between temperature
increase and amount of greenhouse gases
in the atmosphere.
– Human activity greatly increases amounts
of greenhouse gases in atmosphere.
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Changes in Average Global Temperature
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Causes of Global Warming and Climate Change
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Greenhouse Effect
– Greenhouse gases allow sunlight to
penetrate the atmosphere.
– Absorbed by earth’s surface.
– Reradiated as infrared energy (heat).
 Absorbed by gases.
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Greenhouse Effect
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Greenhouse Effect
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Carbon Dioxide
– Fossil fuel burning, deforestation.
Chlorofluorocarbons
– Refrigerants, cleaning solvents, propellants.
Methane
– Breakdown of organic material by
anaerobic material.
Nitrous Oxide
– Biomass burning - Breakdown of nitrogenrich products.
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Potential Consequences of Global Warming
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Rising Sea Level
– Beach and coastal wetland erosion.
Disruption of Water Cycle
– Navigation
– Hydropower
– Water Supply and Demand
– Flood Control
– Environmental Quality and Recreation
– Political Issues
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Potential Consequences of Global Warming
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Health Effects
– Most direct effect of climate change would
be impacts of hotter temperatures.
 Hot temperatures force cardiovascular
system to work harder to cool the body.
 Heat exhaustion and some
respiratory problems increase.
 Aggravate air quality problems.
 Ozone
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Potential Consequences of Global Warming
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Changing Forests
– Geographic distributions of vegetation.
Challenges to Agriculture
– Increased CO2 concentration likely to
increase crop yields in some areas and
decrease yields in other areas.
– Pest range expansion could increase
vulnerability.
Unanticipated Changes
– Greatest risks may be those yet to be
discovered.
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Effects of Global Warming
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Addressing Climate Change
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Energy Efficiency
– Increase efficiency of energy utilization.
 Reduce carbon dioxide production.
 Carbon Tax
Role of Biomass
– Increase amount of carbon dioxide
removed from the atmosphere.
 Increased vegetation growth.
 Short-term benefit.
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Addressing Climate Change
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Political and Economic Forces
– Will be difficult to achieve global
consensus to reduce CO2 emissions, as
CO2 is released as a result of energy
consumption which affects all sections of
the economy.
 Resources and policies to increase
investment in renewables and other
long-term technologies will be needed.
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Indoor Air Pollution
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Growing evidence indicates air within homes
and other buildings can be more seriously
polluted than industrialized cities.
– Adverse effects on human health.
 Asbestos
 Formaldehyde
 Airborne Pesticide Residues
 Perchloroethylene
 Paradichlorobenzene
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Indoor Air Pollution
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Smoking most important pollutant.
Weatherizing to increase efficiency slows air
exchange and tends to trap pollutants.
Average person spends almost 90% of time
indoors.
– Movements to reduce indoor air pollution
lag behind regulations governing outdoor
air pollution.
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Review
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The Atmosphere
Categories of Air Pollutants
Control of Air Pollutants
Acid Deposition
Ozone Depletion
Global Warming and Climate Change
Addressing Climate Change
Indoor Air Pollution
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