Transcript Understanding Our Environment

Air Pollution
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THE AIR AROUND US
 Air pollution-physical or chemical changes brought
about by natural processes or human activities that
result in the decrease of air quality
 ~147 million metric tons annually in US
– Worldwide ~2 billion metric tons.
 Improving air quality in developed countries,
developing getting worse.
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NATURAL SOURCES OF AIR
POLLUTION
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Natural Fires - Smoke
Volcanoes - Ash and acidic components
Sea Spray - Sulfur
Bacterial Metabolism - Methane
Dust
Pollen
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HUMAN-CAUSED AIR
POLLUTION
 Primary Pollutants – emitted directly into air
from a point source
 Secondary Pollutants – formed in air when
primary pollutants react or interact
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Major Sources of Primary Pollutants
Stationary Sources
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Combustion of fuels for power and heat – Power Plants
Burning wood, crops, and/or forest fires
Industry
Solvents and aerosols
Mobile Sources
 Highway: cars, trucks, buses and motorcycles
 Off-highway: aircraft, boats, locomotives, farm
equipment, RVs, construction machinery, and lawn
mowers
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Major Air Pollutants
• Carbon monoxide (CO)
• Nitrogen dioxides (NO2)
• Ozone (O3)
• Particulate matter (PM-10, PM-2.5)
• Sulfur dioxide (SO2)
• Lead (Pb)
• Greenhouse gases (CO2 and others)
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Carbon Monoxides*
 Properties: colorless, odorless, 0.0036% of
atmosphere
 Effects: reduces ability of blood to bring oxygen to
body cells and tissues, mental functions and visual
acuity, even at low levels
 Sources: incomplete combustion of fossil fuels and
combustion of waste
– 60 - 95% from auto exhaust
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Sulfur Dioxides*
 Properties: colorless gas with irritating odor
 Effects:
– reacts in atmosphere to create SO3 and H2SO4
– breathing difficulties
 Sources:
– Natural: sea spray, volcanic fumes
– Human sources: burning high sulfur coal or oil,
smelting or metals, paper manufacture
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Particulate Matter*
Properties: particles suspended in air (<10 um)
Effects: Inhalation causes respiratory diseases,
ranging from asthma to respiratory distress and lung
cancer, reduces visibility
Sources:
–Natural: dust, volcanic ash, pollen, spores
–Human sources: Smoke, dust, soot, asbestos, factories,
unpaved roads, plowing, lint, burning fields
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Particulate Matter
• Impacts: Visibility at Shenandoah Nat’l Park
Source: Ref. (2)
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Nitrogen Dioxides*
 Properties: reddish brown gas, strong oxidizing
agent, forms Nitric acid in air
 Effects: lung and heart problems, component of
photochemical smog and acid deposition,
suppresses plant growth
 Sources:
– Natural: forest fires, volcanoes, lightning, bacteria in
soil
– Human sources: fossil fuels combustion and power
plants
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Lead*
 Properties: grayish metal
 Effects: accumulates in tissue; affects kidneys,
liver and nervous system (children most
susceptible); mental retardation; possible
carcinogen; 20% of inner city kids have high levels
 Sources: particulates, melting smelting, batteries
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Ground Level Ozone*
 Properties: colorless, unpleasant odor, major part of
photochemical smog
 Effects: lung irritant, damages plants, rubber, fabric,
eye, reduces visibility
 Sources: Created by sunlight acting on NOx and VOCs
NOx + VOCs + sunlight -> NOx + O3
cars, industry, gas vapors, chemical solvents,
incomplete fuel combustion products
 10,000 to 15,000 people in US admitted to hospitals
each year due to ozone-related illness
 Children more susceptible
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VOCs
 Properties: organic compounds (hydrocarbons) that
evaporate easily, usually aromatic
 Effects: eye and respiratory irritants; carcinogenic;
liver, CNS, or kidney damage; damages plants; lowered
visibility due to brown haze; global warming
 Sources: vehicles (largest source), evaporation of
solvents or fossil fuels, aerosols, paint thinners, dry
cleaning
 Concentrations indoors up to 1000x outdoors
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Formation & Intensity
Factors
 Local climate (inversions, air pressure, temperature,
humidity)
 Topography (hills and mountains)
 Population density
 Amount of industry
 Fuels used by population and industry for heating,
manufacturing, transportation, power
 Weather: rain, snow,wind
 Buildings (slow wind speed)
 Mass transit used
 Economics
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Photochemical Smog Forms
...when polluted air is stagnant
(weather conditions, geographic location)
Los Angeles, CA
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Primary Pollutants
CO CO2
SO2 NO NO2
Most hydrocarbons
Most suspended
particles
Natural
Sources
Secondary Pollutants
SO3
HNO3
H 2 O2
H2SO4
O3
PANs
–
Most NO3
Stationary
Mobile
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Photochemical Smog
UV radiation
Primary Pollutants
Secondary Pollutants
NO2 + Hydrocarbons
HNO3
O3
nitric acid ozone
H2O + O2
Auto Emissions
Photochemical Smog
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Temperature Inversions
 Occurs when a stable layer of warm air overlay
cooler air near the ground
– Usually happens at night since ground loses heat
quickly
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Heat Islands
 Heat islands-Urban development creates warm,
stable air masses over large cities.
– Sparse vegetation and dark surfaces
– Concentrates pollutants in a “dust dome”.
 Rural areas downwind have decreased visibility and
increased rainfall.
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Acid Deposition
• Occurs when sulfur dioxide and nitrogen oxides are
emitted into the atmosphere
– Coal burning plants
– Automobiles
• Absorbed by water droplets in clouds
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Secondary Pollutants
Primary Pollutants
SO2
NO2
H2SO4
HNO2
sulfuric acid nitric acid
acidic precipitation
vegetation
direct toxicity
indirect health effects
water
Fossil fuels
Power plants
Industrial emissions
soils
sediments
Auto emissions leaching of mineralsleaching aluminum
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2 Forms of Acid Deposition
 Wet deposition-acidic rain, fog, snow and cloud
vapor
– Falls in downward winds areas within 4-14 days
 Dry deposition-acidic particles and gases
– Falls near the emission sources within 2-3 days
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Acidic
Precipitation
Wind
Transformation to
sulfuric acid (H2SO4)
and nitric acid (HNO3)
Windborne ammonia gas
and particles of cultivated soil
partially neutralize acids and
form dry sulfate and nitrate salts
Sulfur dioxide (SO2)
Nitric oxide (NO)
and NO
Acid fog
Ocean
Dry acid
deposition
(sulfur dioxide
gas and particles
of sulfate and
nitrate salts)
Wet acid deposition
(droplets of H2SO4 and
HNO3 dissolved in rain
and snow)
Farm
Lakes in
deep soil
high in limestone
are buffered
Lakes in shallow
soil low in
limestone
become
acidic
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Factors that effect…
• The strength of the effects depend on many
factors
– How acidic the water is
– The chemistry and buffering capacity of
the soils involved
– The types of fish, trees, and other living
things that rely on the water
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Effects of Acid Rain
• Damages forests and soils, fish and other
organisms, materials, and human health.
• most clearly seen in the aquatic environments
• young of most species are more sensitive
• At pH 5, most fish eggs cannot hatch.
• At lower pH levels, some adult fish die.
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Effects of Acid Rain
• Acidic water
– dissolves the nutrients and helpful minerals in
the soil
– washes them away before uptake from plants
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Buffering Capacity
• Acid rain primarily affects sensitive
bodies of water
• soils have a limited “buffering capacity”
• Lakes and streams become acidic
• When low, acid rain also releases aluminum
from soils into lakes and streams
• Aluminum is highly toxic to many species of
aquatic organisms.
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Mongolia
Germany
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Great Smoky
Mountains, NC
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Ozone – Two Faces
• Stratosphere – Good Ozone
–Blocks UV radiation
–Hole caused by depletion due to
CFC’s
• Troposphere – Bad Ozone
–Pollution
• Photochemical smog
• Eye irritant
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Ozone Formation
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Destroying Good Ozone
• Chloroflourocarbons created in 1928 as non-toxic,
non-flamable refrigerants
• first produced commercially in the 1930's by DuPont
• In 1974, a laboratory study demonstrated the ability
of CFC's to breakdown Ozone in the presence of high
frequency UV light
• Cl + O3 -> ClO + O2 ClO + O3 ---> 2 O2 + Cl
• In a 1985, a study summarized data that had been
collected by the British Antartic Survey showing that
ozone levels had dropped to 10% below normal
January levels for Antarctica.
•37 http://www.nas.nasa.gov/About/Education/Ozone/history.html
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Destruction of Stratospheric Ozone
•CFCs persist up in the atmosphere for decades
•Models indicate that 75-85% of the observed
ozone losses in the stratosphere since 1976 are
the result of ozone depleting chemicals
released in the early 1950s
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http://www.mmscrusaders.com/newscirocks/ozone/cfc.jpg
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Stratospheric Ozone
 Winds isolate Antarctic air and allows
stratospheric temperatures to drop and create ice
crystals at high altitudes.
– ozone and chlorine molecules are absorbed on the
surfaces of these ice particles.
 When sun returns in the spring and provides energy
chlorine molecules are released
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Harmful effects of UV radiation
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Skin cancer
Cataracts and sun burning
Adverse impact on crops and animals
Alters photochemical reaction rates
Increases smog and surface layer ozone
Degradation of paints and plastic material
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Montreal Protocol
 An international treaty designed to protect the
ozone layer
 Phasing out production of number of substances
believed to be responsible for ozone depletion
 Effective January 1, 1989
– Five revisions
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1990 (London)
1992 (Copenhagen)
1995 (Vienna)
1997 (Montreal)
1999 (Beijing)
 As a result CFC production fell 85%
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