Chapter 17 Topics:
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The Earth’s atmosphere
Weather, climate, and
atmospheric conditions
Outdoor pollution
Stratospheric ozone
depletion
Acidic deposition and
consequences
Indoor air pollution
The atmosphere – its composition
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Atmosphere = the thin layer of gases around Earth
A
reservoir for nitrogen, carbon, and oxygen
 Absorbs radiant energy and moderates climate
 Transports and cycles water vapor
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Major gases – 78% N2 and 21% O2
Minor gases
 Permanent
– Argon, Neon, Helium, Hydrogen, Xenon
 Variable – water vapor, CO2, CH4, O3, CFCs
The atmosphere has layers
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The layers of the
atmosphere are defined by
vertical variations in its
temperature
The variations occur
because the atmosphere is
heated at three places
The Earth’s surface
 The Stratospheric ozone
layer
 The outer edge of the
atmosphere
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Our layer – the troposphere
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Troposphere = layer closest to Earth (0 to 7 miles)
 Heated
by infrared energy given off by Earth’s surface
 Visible
light is absorbed by Earth’s surface, warming it
 Earth’s “warm” surface gives off infrared light
 Certain gases in the troposphere absorb the infrared light
 Temperature
decreases with altitude
 Contains most of the water vapor
 Our weather occurs in this layer
 Upper boundary is the tropopause – a real boundary
The overlying layers
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Stratosphere = second layer (7 to 31 mi)
 Heated
by ultraviolet light absorbed in the ozone layer
 Temperature increases with altitude
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Mesosphere = third layer (31to 56 mi)
 Heated
by ultraviolet light absorbed in the ozone layer
 Temperature decreases with altitude
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Stratosphere = second layer (56+ mi)
 Heated
by high-energy light absorbed at the outer
edges of the atmosphere
 Temperature increases with altitude
Some atmospheric properties
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Atmospheric pressure = the force per unit area
produced by a column of air, atmospheric pressure
decreases with altitude
Relative humidity = the amount of water vapor in
the air as a percentage of the amount that could be
in the air (at a given temperature)
 Dew
point – temperature at which the relative humidity
is 100% (the air is “saturated”) – condensation occurs
 As air cools, its relative humidity increases;
as air warms, its relative humidity decreases
Uneven heating…
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The surface of the Earth is unevenly heated because
sunlight strikes the curved surface of the Earth at
different angles
Tropical zone (30°N to 30°S)
 Sunlight
strikes the surface at high angles (60°-90° as
measured from the horizon) – this is “direct” sunlight
 Solar energy is more intense, it is concentrated in a
smaller area – this zone is warmer than other zones
…of Earth’s surface…
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Polar zone (60°N/S to 90°N/S)
 Sunlight
strikes the surface at low angles (0°-30° as
measured from the horizon) – this is “indirect” sunlight
 Solar energy is less intense, it is spread out over a
larger area – this zone is colder than other zones
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Temperate zone (30°N/S to 60°N/S)
 Sunlight
strikes the surface at different angles during
different times of the year (due to axial tilt)
 These zones receive more energy when their pole is
tilted toward the sun – the sunlight angle is more direct
…causes seasons…
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Earth’s seasons are caused by the tilt of Earth’s axis
(NOT!! the distance between the Earth and the sun)
As Earth revolves
around the sun, the
tilt of its axis causes
different regions
to receive direct
and/or indirect
sunlight at different
times of the year
…and movement of the air
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The troposphere is heated from the bottom, by the
(unevenly) heated surface of the Earth
This makes the
troposphere density
unstable and induces
convective circulation
 Warm,
less dense air
rises
 Cool, denser air sinks
Global convection = global winds
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If things were simple
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But they’re not
Convection cells & global winds
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Hadley Cell – air rises at 0°, travels north and south
along the tropopause, and sinks at 30°N/S
 At 30°N/S, air moves back toward the equator
across Earth’s surface, becoming the Trade Winds
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Ferrel Cell – air rises at 60°N/S, travels south and north
along the tropopause, and sinks at 30°N/S
 At 30°N/S, air moves back toward 60°N/S
across Earth’s surface, becoming the Westerlies
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Polar Cell – air rises at 60°N/S, travels north and south
along the tropopause, and sinks at 90°N/S
 At 90°N/S, air moves back toward 60°N/S
across Earth’s surface, becoming the Polar Easterlies
Convection cells & global winds
Weather vs. climate
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Weather and climate involve the physical properties of
the troposphere – temperature, pressure, humidity,
cloudiness, wind, etc.
Weather = specifies atmospheric conditions over short
time periods and within small geographic areas
Climate = patterns of atmospheric conditions across
large geographic regions over long periods of time
(generally 30-year averages of weather conditions)
Mark Twain said, “Climate is what we expect; weather
is what we get”
Air masses and fronts
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Air Mass = a large body of air that take on the
characteristics of the area over which it forms
Two main characteristics – temperature & humidity
 Temperature
– Tropical (warm, hot) or Polar (cool, cold)
 Humidity – Maritime (moist) or Continental (dry)
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Air masses move in response to the global winds
Fronts = the boundaries between air masses
moving at different rates and in different directions
Weather changes along fronts
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Cold front = when
colder, drier air pushes
into & displaces
warmer, moister air
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Warm front = when
warmer, moister air
pushes into & displaces
colder, drier air
Pressure systems influence weather
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High-pressure system = air that sinks because it is
cool, spreading outward as it nears the ground
 Sinking
air means no clouds
 Sunny conditions and fair weather
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Low-pressure system = air that rises because it is
warm, drawing air inward toward its center
 Rising
air means clouds (cooling and
condensation)
 Cloudy conditions and rainy weather
Thermal inversion
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Sometimes (particularly in valleys)
a layer of warm air becomes
situated above cooler air –
“inverting” the usual temperature
change with altitude
As at the tropopause, rising air is
blocked by the warm air layer
(the rising air is cooler, denser)
If the rising air contains pollutants,
these are trapped below the
“thermal inversion”
Storms
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Tropical cyclones = large, low pressure weather
systems fed by the energy of tropical moisture
 Called
hurricanes in the western hemisphere
and typhoons in the eastern hemisphere
 Wind speeds greater than 72 mph; heavy rains can
cause flooding, storm surges can inundate coastal areas
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Tornadoes = a funnel-shaped zone of high winds
 Form
in severe thunderstorms due to very high,
localized wind shear
 Much smaller scale than tropical cyclones
Air pollution
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The presence in the atmosphere of air pollutants,
particulate matter [liquid and solid] and gases that
can harm people, harm other organisms, or affect
climate
The concepts of point-source and non-point-source
pollution apply to air pollution
Air pollution sources are also evaluated and
regulated as “mobile” and “stationary” sources
Aerosols
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Aerosols = fine particulate matter (liquid and solid)
suspended in the atmosphere
 Reflect
sunlight back to space
 Cool Earth’s surface and therefore, the troposphere
 Volcanic dust,
sulfate particulates,
soot, desert dust,
clouds
Natural sources of air pollution
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Volcanic eruptions can release large volumes of
particulate matter, sulfur dioxide, and other gases
Forest fires release soot and gases
Dust from arid regions can be carried across oceans
Types of air pollutants
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Primary pollutants = harmful materials emitted
directly into the atmosphere (soot, sulfur dioxide)
Secondary pollutants = harmful materials that
form when primary pollutants interact with each
other or react with components of the atmosphere
(smog)
Criteria pollutants = pollutants that pose especially
great threats to human health: carbon monoxide,
sulfur dioxide, nitrogen oxides, tropospheric ozone,
particulate matter, lead
Criteria pollutants: CO and SO2
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Carbon monoxide (CO) = colorless, odorless gas
 Produced
primarily by incomplete combustion of fuel
 From vehicles and engines, industry, waste combustion,
residential wood burning
 Poses risk to humans and animals, even in small
concentrations
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Sulfur dioxide (SO2) = colorless gas, strong odor
 Coal
emissions from electricity generation, industry
 Can form acid precipitation
Nitrogen oxides and trop. ozone
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Nitrogen oxides (NOx) = formed when nitrogen and
oxygen react at high temperatures in engines
Nitrogen dioxide (NO2) = a highly reactive, foul-smelling
reddish brown gas
 Vehicles, industrial combustion, electrical utilities
 Contribute to smog and acid precipitation
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Tropospheric ozone (O3) = a colorless gas with a
strong odor (a secondary pollutant)
Results from interactions of sunlight, heat, nitrogen oxides,
and volatile carbon-containing chemicals
 Causes respiratory problems
 The pollutant that most frequently exceeds EPA standards
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Particulate matter and lead
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Particulate matter (PM) = solid or liquid particles
suspended in the atmosphere (aerosols)
 Primary
pollutants: dust and soot
 Secondary pollutants: sulfates and nitrates
 Damages respiratory tissue when inhaled
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Lead = a heavy metal
 From
industrial metal smelting (formerly in gasoline)
 Bioaccumulates and damages the nervous system
Local and global effects
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Residence time = the time a pollutant stays in the
atmosphere
Pollutants with brief residence times (PM, SO2) exert
localized impacts over short time periods
Pollutants with long
residence times (CH4,
CFCs) exert regional
or global impacts
Air pollution laws
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Air Pollution Control Act (1963) funded research
and encouraged emissions standards
The Clean Air Act of 1970
 Set
standards for air quality, limits on emissions
 Provided funds for pollution-control research
 Allowed citizens to sue parties violating the standards
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The Clean Air Act of 1990
 Strengthened
regulations for auto emissions, toxic air
pollutants, acidic deposition, stratospheric ozone
depletion
 Introduced emissions trading for sulfur dioxide
The laws are effective
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Emissions reduced and economy improved
 Total
emissions of the six monitored pollutants have
declined 60% since the Clean Air Act of 1970
 Despite increased population, energy consumption,
miles traveled, and gross domestic product
Toxic air pollutants
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Toxic air pollutants = substances that cause: cancer,
reproductive defects, neurological, developmental,
immune system, or respiratory problems
The EPA regulates 188 toxic air pollutants from
metal smelting, sewage treatment, industry, etc.
Include heavy metals, VOCs, diesel emissions
Clean Air Act regulations helped reduce emissions
by more than 35% since 1990
Air pollution in developing countries
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Air pollution is getting worse in developing nations
 Factories
and power plants pollute more as
governments emphasize economic growth, not pollution
control
 People burn
traditional fuels
(wood and charcoal)
and more own cars
Air pollution in China
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China has the world’s worst air pollution
Asian (Atmospheric) Brown Cloud = a 2-mile-thick layer
of pollution over southern Asia
Pollution was an issue during the Olympic in Beijing
The government is trying to decrease pollution
Shutting down heavily
polluting factories
 Installing pollution controls
 Encouraging renewable
and nuclear energy
 Mandating cleaner
burning fuels
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Rural air pollution
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Feedlots, where cattle, hogs, or chickens are raised
in dense concentrations
 Significant
amounts of dust, methane, hydrogen sulfide,
and ammonia, and other objectionable odors
 People living or working nearby have high rates of
respiratory illness
Smog is our most common problem
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Smog = a mixture of air pollutants in urban areas
 Industrial
(gray air) smog = from industries that burn
coal or heavy oil; soot and sulfate particulates
 Photochemical (brown air) smog = a sunlight-induced
collection of secondary air pollutants derived from
automobile exhaust (nitrogen oxides and VOCs)
Making smog
Reducing smog
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New cars required to have catalytic converters
Financial incentives to replace aging vehicles
Annual vehicle inspection programs
Reduction of sulfur content in diesel fuel
Electronic pollution indicator boards raise
awareness
Stratospheric ozone
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Ozone layer = ozone in the lower stratosphere
 Blocks
incoming ultraviolet (UV) radiation
 Protecting life from radiation’s damaging effects
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Ozone-depleting substances = human-made
chemicals that destroy ozone by splitting its
molecules apart
 Halocarbons
= human-made compounds made from
hydrocarbons with added chlorine, bromine, or fluorine
 Chlorofluorocarbons (CFCs) = a halocarbon used as
refrigerants, in fire extinguishers, in aerosol cans, etc.
Ozone depletion
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UV radiation frees a chlorine atom from the CFC
The chlorine atom splits the ozone molecule and
then gives up the third oxygen
One chlorine atom
can destroy
100,000 ozone
molecules
CFCs remain in the
stratosphere for
a century
The Ozone hole
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Ozone hole = decreased ozone levels over
Antarctica
In addition to general depletion of stratospheric
ozone, unique seasonal
weather conditions over
Antarctica cause further
ozone depletion
 Winter
clouds and wind
 Spring releases Cl
 Summer eases winds
 Diffusion “heals” hole
The Montreal Protocol
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Montreal Protocol = 196 nations agreed to cut
CFC production in half by 1998
Follow-up agreements deepened cuts, advanced
timetables, and addressed other ozone-depleting
chemicals
Industry shifted to safer, inexpensive, and efficient
alternatives
Challenges still face us
 CFCs
will remain in the stratosphere for a long time
 Nations can ask for exemptions to the ban
A global environmental success
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The Montreal Protocol is our biggest environmental
success story
Research developed rapidly, along with technology
Policymakers asked industry to help solve the
problem
Many chemical patents were about to expire
Implementation used an adaptive management
strategy
Acid deposition
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Acid deposition = the deposition of acid and acidforming pollutants from the atmosphere onto Earth’s
surface
Although common referred to as “acid rain”, over
half of acid deposition is in the form of dry
particles
Acid deposition originated with the burning fossil
fuels, which release sulfur dioxide and nitrogen
oxides into the atmosphere
Formation of acid rain
Impacts of acid rain
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Affects surface water and kills fish
Leaches nutrients from topsoil
and changes soil chemistry
The acid-neutralizing capacity
of soil or water determines the
severity of acid rain’s effects
Damages agricultural crops
and forests
Erodes stone buildings and
structures
Corrodes cars and exposed
metal
Addressing acid deposition
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Reducing acid deposition involves reducing the
pollution that contributes to it
The Clear Air Act of 1990 established an emissions
trading program for sulfur dioxide
New technologies such as scrubbers have helped
Acid deposition continues to be a problem in the
developing world, especially in China, which burns
coal in factories lacking pollution control equipment
Scrubbers
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Scrubbers =
chemically
convert or
physically
remove
pollutants
before they
leave
smokestacks
Indoor air pollution
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Indoor air pollution = in workplaces, schools, and
homes
Health effects are greater than from outdoor pollution
The average U.S. citizen spends 90% of the time
indoors, exposed to synthetic materials that have not
been comprehensively tested
Being environmentally prudent can make it worse
To reduce heat loss and improve efficiency, ventilation
systems were sealed off
 Windows do not open, trapping pollutants inside
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Tobacco smoke and radon
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The most dangerous indoor pollutants
Secondhand smoke from cigarettes is very
dangerous
 Contains
over 4,000 chemical compounds
 Causes eye, nose, and throat irritation
 Smoking has declined in developed nations
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Radon causes 21,000 deaths a year in the U.S.
A
radioactive gas resulting from natural decay of rock,
soil, or water that can seep into buildings
 New homes are being built that are radon resistant
VOCs pollute indoor air
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The most diverse group of indoor air pollutants
Released by everything from plastics and oils to perfumes
and paints
 Most VOCs are released in very small amounts
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Unclear health implications due to low concentrations
Formaldehyde leaking from pressed wood and insulation
irritates mucous membranes and induces skin allergies
Pesticides seep through floors and walls and are
brought in on shoe soles
Sources of indoor air pollution
Living organisms pollute indoors
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Dust mites and animal dander worsen asthma
Fungi, mold, mildew, airborne bacteria cause
allergies, asthma, other respiratory ailments, and
diseases
Sick building syndrome = a sickness produced by
indoor pollution with general and nonspecific
symptoms
Can be reduced by using low-toxicity building
materials and good ventilation