Air Pollution
• Ozone Depletion
• Outdoor Air Pollutants
– The Clean Air Act
• Industrial Smog and Photochemical Smog
• Acid Deposition
• Indoor Air Pollution
Outdoor air pollution
• Air pollution = material added to the atmosphere
that can affect climate and harm organisms,
including humans
• Air pollution can come from human-made chemicals
and causes, but the majority is from natural sources.
• Government policy and improved technologies have
helped diminish outdoor or ambient air pollution
substantially in developed but not developing
countries.
Natural sources of air pollution
dust storms
volcanoes
fires
Artificial sources of air pollution
Human-caused air pollution includes:
• Point sources = specific spots where large
amounts of pollution are discharged (factory
smokestacks)
• Non-point sources = diffuse, often made up of
many small sources (charcoal fires from
thousands of homes)
Artificial sources of air pollution
Human-caused air pollution includes:
• Primary pollutants = emitted into
troposphere in a directly harmful form (soot,
carbon monoxide)
• Secondary pollutants = produced via
reaction of substances added to the
atmosphere with chemicals already present in
the atmosphere (ozone in troposphere)
Clean Air Act legislation
Major air pollution legislation:
• Clean Air Act of 1970:
•
•
•
•
Set stricter standards than previous laws
Imposed emissions limits
Provided research funds
Enabled citizens to sue violating parties
• Clean Air Act of 1990:
• Strengthened previous regulations
• Introduced emissions trading for sulfur dioxide
Six “criteria pollutants”
The EPA closely tracks six major types of pollutants according
to national ambient air quality standards:
•
Carbon monoxide (CO)
•
Sulfur dioxide (SO2)
• Nitrogen dioxide (NO2)
•
Tropospheric ozone (O3)
•
Particulate matter
•
Lead
CO / SO2 / NO2
• Carbon monoxide (CO) = colorless, odorless gas
from vehicle exhaust and other sources;
dangerous—prevents oxygen uptake
• Sulfur dioxide (SO2) = colorless gas from coal
burning for electricity and industry; contributes to
acid precipitation
• Nitrogen dioxide (NO2) = foul-smelling red gas
from vehicle exhaust, industry, and electricity
generation; contributes to smog and acid
precipitation
O3 / Pb / particulate matter
• Tropospheric ozone (O3) = colorless gas; secondary
pollutant from sunlight, heat, nitrogen oxides (NOx), and Ccontaining chemicals; contributes to smog; harmful to living
tissues
• Lead (Pb) = metal in atmosphere as particulate; from gasoline
additive, phased out in 1980s; diverse health impacts, all bad
• Particulate matter = any solid (or liquid) particles small
enough to be carried aloft in air; dust, soot, sulfates, nitrates;
causes respiratory damage
Table 20-2 Major Outdoor Air Pollutants
CARBON MONOXIDE (CO)
Description: Colorless, odorless gas that is poisonous to air-breathing animals; forms during
the incomplete combustion of carbon-containing fuels (2 C + O2 2 CO).
Major human sources: Cigarette smoking (p. 409), incomplete
burning of fossil fuels. About 77% (95% in cities)comes from motor vehicle exhaust.
Health effects: Reacts with hemoglobin in red blood cells and reduces the ability of blood to
bring oxygen to body cells and tissues. This impairs perception and thinking; slows reflexes;
causes headaches, drowsiness, dizziness, and nausea; can trigger heart attacks and angina;
damages the development of fetuses and young children; and aggravates chronic bronchitis,
emphysema, and anemia. At high levels it causes collapse, coma, irreversible brain cell
damage, and death.
Table 20-2 Major Outdoor Air Pollutants
NITROGEN DIOXIDE (NO2)
Table 20-2
Page 438
Description: Reddish-brown irritating gas that gives photochemical smog its brownish color; in the
atmosphere can be converted to nitric acid (HNO3), a major component of acid deposition.
Major human sources: Fossil fuel burning in motor vehicles (49%) and power and industrial plants (49%).
Health effects: Lung irritation and damage; aggravates asthma and chronic bronchitis; increases
susceptibility to respiratory infections such as the
flu and common colds (especially in young children and older adults).
Environmental effects: Reduces visibility; acid deposition of HNO3 can damage trees, soils, and aquatic life
in lakes.
Property damage: HNO3 can corrode metals and eat away stone on buildings, statues, and monuments; NO2
can damage fabrics.
Table 20-2 Major Outdoor Air Pollutants
SULFUR DIOXIDE (SO2)
Table 20-2
Page 438
Description: Colorless, irritating; forms mostly from the combustion of sulfur containing fossil fuels such as coal
and oil (S + O2 SO2); in the atmosphere
can be converted to sulfuric acid (H2SO4), a major component of acid deposition.
Major human sources: Coal burning in power plants (88%) and industrial processes
(10%).
Health effects: Breathing problems for healthy people; restriction of airways in people with asthma; chronic
exposure can cause a permanent condition similar to bronchitis. According to the WHO, at least 625 million people
are exposed to unsafe levels of sulfur dioxide from fossil fuel burning.
Environmental effects: Reduces visibility; acid deposition of H2SO4 can damage trees, soils, and aquatic life in
lakes.
Property damage: SO2 and H2SO4 can corrode metals and eat away stone on buildings, statues, and
monuments; SO2 can damage paint, paper, and leather.
Table 20-2 Major Outdoor Air Pollutants
Table 20-2
Page 438
SUSPENDED PARTICULATE MATTER (SPM)
Description: Variety of particles and droplets (aerosols) small and light enough to remain suspended in
atmosphere for short periods (large particles) to long periods
(small particles; Figure 20-6, p. 441); cause smoke, dust, and haze.
Major human sources: Burning coal in power and industrial plants (40%), burning diesel and other fuels in
vehicles (17%), agriculture (plowing, burning off fields), unpaved roads, construction.
Health effects: Nose and throat irritation, lung damage, and bronchitis; aggravates bronchitis and asthma;
shortens life; toxic particulates (such as lead, cadmium, PCBs, and dioxins) can cause mutations, reproductive
problems, cancer.
Environmental effects: Reduces visibility; acid deposition of H2SO4 droplets can
damage trees, soils, and aquatic life in lakes.
Property damage: Corrodes metal; soils and discolors buildings, clothes, fabrics, and paints.
Table 20-2 Major Outdoor Air Pollutants
OZONE (O3)
Table 20-2
Page 438
Description: Highly reactive, irritating gas with an unpleasant odor that forms in the troposphere as a major
component of photochemical smog (Figures 20-3 and 20-5).
Major human sources: Chemical reaction with volatile organic compounds (VOCs, emitted mostly by cars and
industries) and nitrogen oxides to form photochemical smog (Figure 20-5).
Health effects: Breathing problems; coughing; eye, nose, and throat irritation; aggravates chronic diseases such
as asthma, bronchitis, emphysema, and heart disease; reduces resistance to colds and pneumonia; may speed
up lung tissue aging.
Environmental effects: Ozone can damage plants and trees; smog can reduce visibility.
Property damage: Damages rubber, fabrics, and paints.
Table 20-2 Major Outdoor Air Pollutants
LEAD
Table 20-2
Page 438
Description: Solid toxic metal and its compounds, emitted into the atmosphere as particulate matter.
Major human sources: Paint old houses), smelters (metal refineries), lead manufacture, storage batteries,
leaded gasoline (being phased out in developed countries).
Health effects: Accumulates in the body; brain and other nervous system damage and mental retardation
(especially in children); digestive and other health problems; some lead-containing chemicals cause cancer in test
animals.
Environmental effects: Can harm wildlife.
Industrial smog
Beijing in March 2012
The U.S. had its own “killer smog” from industrial pollution.
Shown is Donora, Pennsylvania, in 1948, at mid-day.
Subsequent demand for legislation against pollution made
U.S. air much cleaner.
Six “criteria pollutants”
Emissions of all of these, especially lead and
carbon monoxide, have substantially declined
since 1970.
Criteria Pollutants Have Decreased Even as
Population and the Economy Have Grown
Reasons for the decline in U.S. pollution
• Cleaner-burning vehicles and
catalytic converters decrease
carbon monoxide
• Permit-trading programs and clean
coal technologies reduce SO2
emissions
• Scrubbers = technologies that
chemically convert or physically
remove pollutants before they leave
the smokestacks
• Phaseout of leaded gasoline
• Improved technologies and federal
policies
Particulate Removal Technology
Toxic air pollutants
• Toxic air pollutants = chemicals known to
cause serious health or environmental
problems
• Include substances known to cause cancer
and reproductive defects, and substantial
ecological harm
• Most produced by human activities
• 188 toxic air pollutants are regulated under
the 1990 Clean Air Act.
Air Pollution
• Ozone Depletion
• Outdoor Air Pollutants
– The Clean Air Act
• Industrial Smog and Photochemical Smog
• Acid Deposition
• Indoor Air Pollution
Ozone layer
• Not really a layer, but a region of higher-thannormal ozone concentrations (which are still
very low)
• ~17–30 km altitude
• Absorbs ultraviolet (UV) radiation from sun,
protecting organisms on surface from
radiation damage
Atmospheric layers
Temperature
and other
characteristic
s vary with
altitude.
Ozone layer
Tropopause
marks boundary
between
troposphere and
stratosphere.
Layers don’t mix.
Stratospheric ozone depletion
• Ozone at low altitudes = beneficial layer
protecting us from UV radiation
• Ozone layer— ~ 12 parts per million in lower
stratosphere—is enough to absorb UV and
protect us.
• But in the 1960s scientists noticed ozone
concentrations were dropping.
Stratospheric ozone depletion
The Dobson spectrophotometer, invented in 1924, can
infer ozone concentrations from the ground, and
helped scientists detect ozone depletion.
Stratospheric ozone depletion
• In 1985, the “ozone hole” was detected over
Antarctica.
• Ozone levels had declined 40–60% over the
previous decade.
Stratospheric ozone depletion
Scientists worried about the effects of extra cancercausing UV on people, organisms, ecosystems.
The ozone hole
(blue) reached its
greatest extent in
September 2000
(satellite imagery).
Stratospheric ozone depletion
• In 1974, Sherwood Rowland and Mario
Molina pegged the blame on
chlorofluorocarbons (CFCs).
• They won the Nobel Prize for this scientific
detective work.
• CFCs = human-made molecules in which
hydrogens of hydrocarbons are replaced by
chlorine and fluorine atoms
• Mass-produced by industry, in refrigerants
and consumer products like aerosol sprays
Stratospheric ozone depletion
CFCs persist in the stratosphere. They split oxygen atoms off
ozone (O3) to form oxygen (O2).
1 Cl atom
can split
many O3
molecules
CFC – Ozone Reaction
Stratospheric ozone depletion
• In 1987, over 180 nations signed the
Montreal Protocol, which restricted CFC
production globally.
• Follow-up agreements strengthened the pact.
• Today CFC levels are down, and
stratospheric ozone is starting to recover.
• The Montreal Protocol is one of the biggest
environmental success stories of our time.
• We have apparently avoided a major
environmental problem.
Stratospheric ozone depletion
Reasons for success of the Montreal Protocol:
• Government and industry cooperated on
finding solutions (cheap replacement
technologies for CFCs), so battles typical to
environmental debates were minimized.
• Protocol was implemented with “adaptive
management”—ability to fine-tune actions as
time goes on, in response to new data or
conditions.
Effect of Montreal Protocol
•Agriculture and Ozone Depletion
Air Pollution
• Ozone Depletion
• Outdoor Air Pollutants
– The Clean Air Act
• Industrial and Photochemical Smog
• Acid Deposition
• Indoor Air Pollution
Industrial smog
Photochemical smog
• 17.16
Industrial smog
• Smog from industrial pollution, fossil-fuel
combustion
• The kind that blanketed London in 1952
• “Gray air smog”
• Contains soot, sulfur, CO, CO2…
Industrial smog
Beijing in March 2012
The U.S. had its own “killer smog” from industrial pollution.
Shown is Donora, Pennsylvania, in 1948, at mid-day.
Subsequent demand for legislation against pollution made
U.S. air much cleaner.
Industrial smog
Chemistry of
industrial smog:
• Burning sulfur-rich
oil or coal creates
SO2, SO3, sulfuric
acid, ammonium
sulfate.
• Carbon leads to
CO2 and CO.
Photochemical smog
• Smog from reaction of sunlight with pollutants
• The kind that blankets so many American
cities today
• “Brown air smog”
• Contains tropospheric ozone, NO2, VOCs,
100 more…
• Hot sunny days in urban areas create perfect
conditions.
Volatile organic compounds
• “VOCs” are regulated by many governments.
• Large group of potentially harmful carboncontaining chemicals used in industrial
processes.
• Hydrocarbons are one example.
• About half are human-made, half natural.
• VOCs contribute to smog, produce secondary
pollutants.
Photochemical smog
Chemistry of
photochemical
smog:
• Nitric oxide starts
a chain reaction.
• Reaction with
sunlight, water
vapor,
hydrocarbon,
results in over
100 secondary
pollutants.
Causal Loops and Leverage
Photochemical smog
• Mexico City and many of the world’s cities suffer
from the brownish haze of photochemical smog.
• Inversion layers and mountains can trap smog over
certain cities.
Thermal inversion
• Usually, tropospheric air
temperature decreases as
altitude increases
• Warm air rises, causing
vertical mixing
• Thermal inversion = a layer of
cool air occurs beneath a layer of
warmer air
• Inversion layer = the band of
air in which temperature rises
with altitude
• Denser, cooler air at the
bottom of the layer resists
mixing
Thermal inversion
• Usually, tropospheric air
temperature decreases as altitude
increases
– Warm air rises, causing vertical
mixing
• Thermal inversion = a layer of
cool air occurs beneath a layer of
warmer air
– Inversion layer = the band of
air in which temperature rises
with altitude
– Denser, cooler air at the bottom
of the layer resists mixing
Viewpoints: Air pollution
Debra
Knopman
“Simply tightening
regulations…is unlikely to
significantly reduce smog…
Emissions trading is an
economically attractive
supplement to current
technology-based regulations.”
David
McIntosh
“Without additional
[regulatory] measures, 20
million people will live in areas
exceeding EPA’s smog standard
in 2015…there is a lot of work
to do.”
Air Pollution
• Ozone Depletion
• Outdoor Air Pollutants
– The Clean Air Act
• Industrial and Photochemical Smog
• Acid Deposition
• Indoor Air Pollution
Acid deposition
• Acidic deposition = deposition of acidic or
acid-forming pollutants from the atmosphere
onto the Earth as acid rain, acid fog, acid
snow
• One type of atmospheric deposition
• Caused by reaction of pollutants like SO2 and
NO with water, oxygen, and oxidants resulting
in sulfuric acid or nitric acid
• Can have wide-ranging detrimental effects on
ecosystems and the built environment
Acid deposition
Acid deposition is created by reactions in the
atmosphere, and can fall many miles from
where pollution originated.
The Chemical Reactions that Form and
Neutralize Acid Precipitation
Acid deposition
Acidity varies geographically. (Orange = more
acidic) Industrialized areas and regions
downwind of them suffer most. Areas with
Limestone Bedrock are less acidic.
Acid deposition
It also eats away at statues and buildings.
Acid deposition
Acid deposition has killed these conifer trees in
the mountains of North Carolina.
Acid deposition
Acid
precipitation
harms soil
and plants,
and alters
the
chemistry of
ecosystems
.
© Martin Kennedy, University of California-Riverside.
Acid Deposition, Plants, and Soil
 Nutrient
leaching
 Heavy metal
release
 Weakens trees
Fig. 20-11 p. 447
Acid deposition
Acid deposition has killed these conifer trees in
the mountains of North Carolina.
Acid deposition
Following the 1970 Clean Air Act,
• Sulfur emissions have decreased due to:
• Technology (“scrubbers”) to clean smokestacks
• Legislation and a market-based emissions trading
scheme
• But nitrate pollution has risen slightly, and
acidification is not being reversed as many
had hoped.
Particulate Removal Technology
Acid deposition
This can be seen in data from New Hampshire’s Hubbard
Brook Experimental Forest, where acid rain was first studied.
pH has increased (rain has become less acidic) since 1970,
but is still much more acidic than normal rain.
Solutions to Acid Deposition
Fig. 20-12 p. 448
Air Pollution
• Ozone Depletion
• Outdoor Air Pollutants
– The Clean Air Act
• Industrial and Photochemical Smog
• Acid Deposition
• Indoor Air Pollution
Indoor air pollution
• Indoor air spaces generally have MORE pollution
than outdoor spaces.
• U.S. citizens spend 90% of time indoors.
• Countless consumer products and synthetic
chemicals kept indoors are used in our daily lives.
UN estimate for world:
• 2.2 million deaths/year from indoor air pollution
• 0.5 million deaths/year from outdoor air pollution
Indoor air
pollution
More disease from indoor
(orange) pollution than
outdoor (red)
In developing nations, indoor
cooking fires are common,
and a major health risk.
Indoor air pollution
• In developed nations, the 2 biggest threats
seem to be:
• Cigarette smoke: lung cancer risk for smokers and
those inhaling secondhand smoke
• Radon: naturally occurring colorless, odorless gas;
radioactive—seeps up from ground and collects in
buildings; lung cancer risk
• Radon varies
in its
occurrence,
depending on
an area’s
underlying
geology.
• It is best to
have your
home tested
for radon.
Radon
Indoor air pollution risks in the
home
Other indoor air pollution
sources
• Many VOCs pollute indoor air (plastics, oils,
cleaning fluids, adhesives, pesticides,
building materials).
• Tiny living organisms (dust mites, animal
dander, fungi, mold) can produce indoor air
pollution, causing allergies, asthma, etc.
• When the cause of building-related illness is a
mystery, the illness is often called sickbuilding syndrome.
Reducing indoor air pollution
• Buy and use low-toxicity products
• Provide good ventilation
• Limit exposure to plastics, treated wood, pesticides,
cleansing fluids (put in garage, not home)
• Test home for radon
• Test drinking water for lead from pipes
• In developing world, provide ventilation, install
clean-burning stoves, shift to gas
Conclusion
• Indoor air pollution is a potentially serious health
threat.
• Outdoor air pollution has been addressed more
effectively by government legislation and regulation.
• There is much room for improvement in reducing
acidic deposition and photochemical smog.
• This will continue to pose a challenge as lesswealthy nations industrialize.