Chemistry for Changing Times
12th Edition
Hill and Kolb
Chapter 13
Air:
The Breath of Life
John Singer
Jackson Community College, Jackson, MI
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Earth’s Atmosphere: Division
and Composition
The Earth’s atmosphere is divided into four regions:
1. Troposphere: This layer is nearest Earth and contains
nearly all living things. The temperature decreases as
altitude increases in the troposphere.
2. Stratosphere: This layer lies above the troposphere and
contains the protective ozone layer. In this layer,
temperature increases with increasing altitude.
3. Mesosphere: This layer lies above the stratosphere.
4. Thermosphere: This layer lies above the mesosphere.
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Earth’s Atmosphere: Division
and Composition
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Earth’s Atmosphere: Division
and Composition
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Chemistry of the Atmosphere
Nitrogen comprises about 78% of all gases in
the atmosphere. All animals and most plants
cannot use the nitrogen available in the
atmosphere as N2 molecules. Organisms must
first “fix” or use “fixed” nitrogen. Fixed means
that the nitrogen atoms are combined with
another element.
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Chemistry of the Atmosphere
Lightning can fix nitrogen as follows:
N2 + O2 + energy (lightning) → 2 NO
2 NO + O2 → 2 NO2
Nitrogen dioxide can then react with water, forming
nitric acid.
3 NO2 + H2O → 2 HNO3 + NO
The nitric acid in rainfall contributes to available
“fixed” nitrogen in the oceans and soil.
Unfortunately, it also acidifies lakes and streams.
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Chemistry of the Atmosphere
Nitrogen can also be fixed industrially using the
Haber-Bosch process:
N2 + 3 H2 → 2 NH3
This process has allowed us to increase the
productivity of soil for food production.
Certain plants (legumes) contain bacteria in their
roots that are able to fix nitrogen.
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Chemistry of the Atmosphere
The Nitrogen Cycle
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Chemistry of the Atmosphere
Oxygen Cycle
Oxygen makes
up 21% of
Earth’s
atmosphere.
Oxygen is
cycled as
shown here.
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Chemistry of the Atmosphere
In the stratosphere, oxygen molecules react to
form ozone, which is capable of absorbing
harmful ultraviolet radiation.
3 O2(g) + UV radiation → 2 O3(g)
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Temperature Inversion
A temperature inversion occurs when cold air
is trapped near Earth’s surface by a layer of
warmer air. Polluted air can then be trapped
near Earth’s surface.
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Pollution Through the Ages
Wildfires, windblown dust, and volcanic action
can all contribute to air pollution.
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A Closed Ecosystem?
The earth is a closed
ecosystem. What you
see is what you get.
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The Air Our Ancestors Breathed
Air pollution has always been with us.
Humans have always altered their environment.
Clearing of land and use of fire have always
impacted the atmosphere.
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Pollution Goes Global
A pollutant is any substance in the wrong place
at the wrong time.
With increased urbanization and globalization,
air pollution has become a global concern.
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Air Pollution in China
As China industrializes
its economy, its people
are experiencing
tremendous air
pollution.
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Industrial Smog
The term smog is a
contraction of smoke
and fog.
Air that has been
polluted by industrial
activity is called
industrial smog.
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Chemistry of Industrial Smog
Oxides of Carbon
When coal (mostly carbon) is burned, carbon
dioxide, carbon monoxide, and soot are
produced:
C(s) + O2(g) → CO2(g)
2 C(s) + O2(g) → 2 CO(g)
Unburned carbon is soot.
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Chemistry of Industrial Smog
Oxides of Sulfur
Coal containing sulfur produces sulfur dioxide:
S(s) + O2(g) → SO2(g)
The sulfur dioxide is further oxidized to sulfur
trioxide:
2 SO2(g) + O2(g) → 2 SO3(g)
Sulfur trioxide can then react with water, forming
sulfuric acid.
SO3(g)+ H2O (l) → H2SO4(l)
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Chemistry of Industrial Smog
Particulate matter (PM) is the solid and liquid
particles that are larger than individual
molecules. Much of particulate matter consists of
unburned minerals found in coal. Some PM
remains in the combustion chamber as bottom
ash, but much flies out the stack as fly ash.
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Chemistry of Industrial Smog
The United States Environmental Protection
Agency estimates that as many as 40,000
premature deaths occur each year due to PM.
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Heath and Environmental
Effects of Industrial Smog
Health
Sulfuric acid and smaller particulates act
synergistically to harm health. The alveoli of the
lungs lose resiliency and this lung damage can
lead to pulmonary emphysema characterized by
shortness of breath.
Environmental
Acidic precipitation and smaller particulates can
damage plants, including farm crops.
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What to Do About Industrial
Smog
Electrostatic precipitators
induce electrostatic charges
on particulates. The charged
particulates are then
attracted to the oppositely
charged plate and deposited.
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What to Do About Industrial
Smog
Bag filtration works like a giant vacuum
cleaner. Flue gases are passed through a series
of filters in a bag house, which removes
particulates.
A cyclone separator works by cycling stack
gases in a spiral motion. Heavier particulates hit
the outer walls of the separator and deposit out
of the gas stream.
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What to Do About Industrial
Smog
Wet scrubbers remove particulates by passing
the stack gases through water.
Sulfur dioxide can be reduced by either
removing sulfur from coal before combustion or
by adding limestone (CaCO3) to the coal.
CaCO3 + heat → CaO(s) + CO2(g)
CaO(s) + SO2(g) → CaSO3(s)
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Automobile Emissions
Gasoline is a mixture of many hydrocarbons with
carbon numbering from about 5 to 12.
Octane (C8H18) is a reasonable representative for
gasoline. Octane undergoes complete combustion
as follows:
2 C8H18(l) + O2 → 18 H2O(g) + 16 CO2(g)
Most internal combustion engines do not burn fuel
to complete combustion.
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Automobile Emissions
Carbon Monoxide
When not enough oxygen is
available for complete combustion,
carbon monoxide (CO) is produced.
Many metric tons of CO are
released into the atmosphere from
automotive exhaust each year.
Carbon monoxide is a toxic,
colorless, odorless, and tasteless
gas.
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Automobile Emissions
Carbon Monoxide
Carbon monoxide bonds with the
hemoglobin in blood. Many
hundreds of people each year
die from carbon monoxide
poisoning.
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Automobile Emissions
Nitrogen Oxides
When nitrogen in the air combines with oxygen
at the high temperatures within an automotive
engine, nitrogen oxides are produced.
N2(g) + O2(g) → 2 NO(g)
Nitrogen monoxide can then oxidize to nitrogen
dioxide.
2 NO(g) + O2(g) → 2 NO2(g)
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Nitrogen Oxides
Nitrogen oxides: Together, nitrogen monoxide
and nitrogen dioxide are known as NOx. These
oxides react with water in the atmosphere to
form nitrous and nitric acids. They lead to smog
formation and are components of acid rain.
Breathing high concentrations of NOx can lead to
serious lung complications.
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Automobile Emissions
Volatile organic compounds (VOCs) are major
contributors to smog formation. They are
produced by the evaporation of gasoline,
unburned fuel in exhaust, paints, and consumer
products. Most VOCs are hydrocarbons. Some
are released from natural sources.
Alkenes can react with oxygen or ozone to form
aldehydes.
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Automobile Emissions
Peroxyacetyl nitrate (PAN = CH3CO3NO2) can
be produced by the reaction of certain
hydrocarbons with oxygen and nitrogen dioxide.
PAN, ozone, and aldehydes are responsible for
many of the harmful effects of smog.
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Photochemical Smog
The components of smog react with sunlight to
form an amber haze known as photochemical
smog.
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Photochemical Smog
Development of
Air Pollutants on a
Typical Sunny
Summer Day
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Solutions to Photochemical
Smog
Reducing the quantities of the pollutants
entering the atmosphere is the answer to how to
reduce photochemical smog. Improved design of
gasoline storage and dispensing systems
reduces the emissions of hydrocarbon VOCs.
Catalytic converters reduce hydrocarbon and
carbon monoxide emissions from automobiles.
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Acid Rain
Acid rain is defined as precipitation having a pH
of less than 5.6. Sulfur oxides and nitrogen
oxides can react with water forming sulfuric and
nitric acids. These are the major contributors to
acid rain.
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Acid Rain
Acid rain is
destructive to
both the natural
and man-made
environment.
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Indoor Air Pollution
Indoor air pollution is a major health concern.
The EPA estimates that pollutant levels of indoor
air ranges from 2 to 100 times higher than the
levels of outdoor air.
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Indoor Air Pollution
CO and NOx are released by gas kitchen
stoves, cigarette smoke, and free-standing
unvented kerosene heaters.
Mold will grow wherever there is moisture. Mold
spores can exacerbate asthma, bronchitis, and
other lung diseases.
Ozone is released from copy machines,
electronic air cleaners, and other devices.
Ozone is a respiratory tract irritant.
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Indoor Air Pollution
Cigarettes and Secondhand Smoke
Cigarette smoke has been shown to contain at
least 40 different carcinogens. The EPA
considers secondhand smoke to be a Class A
carcinogen. Regular exposure to smoke and
secondhand smoke has been shown to increase
the risk of heart disease, lung cancer,
miscarriage, and sudden infant death syndrome
(SIDS).
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Indoor Air Pollution
Radon is a radioactive noble gas. It is colorless,
odorless, and tasteless. Radon is released
naturally from rock and soil. Radon decays by
alpha emission.
Polonium-218 is a daughter isotope of radon. It
deposits in lung tissue and continues to emit
radiation.
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Ozone: The Double-Edged
Sword
Ozone (O3) is an allotrope of oxygen (O2).
Ozone in the troposphere is a hazardous, toxic
substance. It contributes to smog and indoor air
pollution.
Ozone in the stratosphere shields life on Earth
from harmful ultraviolet radiation.
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Ozone: The Double-Edged
Sword
In the mesosphere, short wavelength ultraviolet
radiation splits oxygen molecules into oxygen
atoms.
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Ozone: The Double-Edged
Sword
Some of these reactive oxygen atoms diffuse to
the stratosphere where they react with oxygen
molecules to form ozone.
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Ozone: The Double-Edged
Sword
The ozone in the stratosphere can absorb longer
wavelength ultraviolet radiation as follows:
O3(g) + UV radiation → O2(g) + O(g)
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Ozone: The Double-Edged
Sword
Chlorofluorocarbons (CFCs) have been shown
to contribute to the destruction. At one time, CFCs
were the propellants used in aerosol cans,
foaming agents, and refrigerants.
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Ozone: The Double-Edged
Sword
Many countries have banned the use of CFCs.
Effective substitutes have been developed.
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Ozone: The Double-Edged
Sword
The Ozone Hole Over Antarctica
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Carbon Dioxide and Climate
Change
Greenhouse Effect
Carbon dioxide (CO2) is known as a greenhouse
gas. CO2 and some other gases will allow solar
energy to penetrate the atmosphere, but trap
heat in (much like a greenhouse).
Human activity has contributed tremendous
amounts of CO2 to the atmosphere in recent
decades. There is much evidence to show that
global warming is indeed occurring.
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Carbon Dioxide and the
Greenhouse Effect
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Greenhouse Gases and Global
Warming
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Climate Change and Weather
As Earth’s climate changes, impacts on food
production, flooding, and increases in infectious
diseases are predicted.
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Mitigation of Global Warming
Reducing the output of greenhouse gases has
no easy fix. Combinations of emerging
technologies, such as solar, nuclear, and wind,
along with carbon sequestration, are potential
answers.
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Who Pollutes? Who Pays?
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Who Pollutes? How Much?
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Paying the Price
Air pollution costs us
tens of billions of
dollars each year.
There is no cheap
and easy fix.
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