Download Ch. 15 Air Pollution and Ozone Depletion

Chapter 15
Air Pollution and Stratospheric Ozone
Depletion
Chattanooga, Tennessee
Declared one of the worst cities in the
US for particulate air pollution!
• 1957- due to the economic boom and the fact
that Chattanooga is located in a bowl, the city air
is found to be highly polluted and causing
respiratory diseases well above the nation’s
average.
• 1970- Clean Air Act and local ordinances,
changed the way in which the city operated and
put major emission controls in place. Three years
later, the city achieved compliance.
Air Pollution
• Defined as the introduction of chemicals,
particulate matter, or microorganisms into
the atmosphere at concentrations high
enough to harm plants, animals, and
buildings, or to alter ecosystems in the
troposphere (first 10 miles above the surface).
• Can occur naturally (volcanoes) or it can be
anthropogenic.
• Air pollution is a global issue.
Pollutant
Sources
• Natural Sources:
– forest fires, volcanoes, and oceanic salt,
• Anthropogenic Sources:
– power plants, newly plowed fields, motor vehicles, etc.
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Major Air Pollutants
• SO2- comes from burning fossil fuels. It
adversely affects plant tissue and is a
respiratory irritant.
• NOx- with the air being 78% N2, all combustion
leads to formation of nitrogen oxides. Mainly
formed from motor vehicles and stationary
fossil fuel combustion as well as forest fires,
lightening and microbial action in soils.
• COx- CO formed during incomplete
combustion, CO2 during complete combustion.
• Particulate Matter (PM)- solid or liquid
particles suspended in the air. Released from
the combustion of fossil fuels, road dust, rockcrushing operations, dust storms, volcanic
eruptions and forest fires. It is a respiratory
irritant and scatters and absorbs sunlight
reducing photosynthesis and producing haze.
• Photochemical Oxidants including
tropospheric Ozone- formed as a result of
sunlight acting on compounds of NOx and SO2
Ozone- O3
• Most frequently measured and abundant
photochemical oxidant in the troposphere.
• Harmful to plants and animals, causes asthma
and emphysema
• Can enhance the formation of particulate
matter and create smog (smoke, fog, ) when
combined with Nox and SO2.
Smog Formation
• During the day, the sun heats up the surface of the
Earth such that warmer air usually resides closer to the
surface of the Earth, with temperatures decreasing
with increasing altitude. At night, the situation is
reversed with cooler air near the surface and warmer
resting on top-resulting in what is known as
temperature inversion. Because basic physics dictates
that warmer air rises and cooler air falls, air pollutants
are simply carried up by the warmer air into the
atmosphere where they are dispersed and diluted.
Thus, the lower atmosphere is cleansed of any
pollutants that accumulate.
• In a situation where temperature inversion exists
during the day, the air near the surface of the Earth is
not hot enough as to allow the warm air to rise into
the atmosphere. In such a case, air pollutants
accumulate near the surface of the Earth, reaching
dangerous threshold levels
• Because temperature inversion is present, it
effectively acts as a thermal lid, thus preventing the
air pollutants from rising and dispersing into
harmless levels in the atmosphere. As a result, a
smog siege can occur.
• Pb - occurs as trace metal in rocks and soil.
When added to gasoline to enhance vehicle
performance and burned it was released into
the air. It has since been removed in the US
but not globally. Pb is toxic to the CNS and can
affect intelligence in children.
• Hg- another trace metal found in coal and oil
and when burned is released into the air. It is
toxic to the CNS as it bioaccumulates in fish
and in humans.
Volatile Organic Compounds
• Organic compounds that become vapors at
typical atmospheric temperatures
• Many VOCs are hydrocarbons (gasoline, lighter
fluid, dry-cleaning fluid, perfumes) that give
off strong odors
• Play an important role in the formation of
photochemical oxidants like ozone.
Primary and Secondary Pollutants
• Primary- are compounds that come directly
out of the smokestacks, exhaust pipes, or
natural emission source. They include: CO,
CO2, SO2, NOx and most suspended particulate
matter.
• Secondary- come from primary pollutants that
have undergone transformation in the
presence of sunlight, water, oxygen or other
compounds. Ex: O3, SO42-, NO31-
Factors affecting transport
• Wind-Higher wind speeds disperse pollutants more
quickly reducing local concentrations
• Stability -Temperature inversion associated with stable
conditions can inhibit the vertical motion of a pollutant
• Turbulence-is the horizontal and vertical motion of the
atmosphere; it can cause mixing and dispersal
• Topography- can act as a physical barrier to pollution
movement.
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Factors affecting transport
http://irina.eas.gatech.edu/lectures/lec17fig4.jpg
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What happens in between?
• TRANSPORT
– Global winds
– Mixing and Cloud Formation
• TRANSFORMATION
– Chemical reactions
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Factors affecting Transformation
• Solar radiation
– Aids in the formation of
ozone
• Humidity &
Precipitation
– Provide moisture
content for pollutants
to bind to  formation
of secondary pollutants
– Cloud formation
Source: aura.gsfc.nasa.gov/outreach/garden_faq.html
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Atmospheric Deposition
• Atmospheric deposition is the process
whereby airborne material is deposited on the
earth's surface.
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Atmospheric Deposition
• Wet
– Wet deposition is the fraction
of atmospheric deposition
contained in precipitation
– Anything attached to water
in some form
• Dry
– Dry deposition is the
fraction deposited in dry
weather through such
processes as settling,
impaction, and adsorption.
– Anything not attached to
water
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Precipitation
• The GOOD:
– washes pollutant particles from the air
– helps to minimize particulate matter formed by
activities such as construction and some industrial
processes.
• The BAD:
– Acid Rain
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• Acid rain causes acidification of lakes and
streams and harms aquatic ecosystems
• Acid rain contributes to the damage of
trees at high elevations (for example, red
spruce trees above 2,000 feet) and many
sensitive forest soils.
• Acid rain accelerates the decay of
building materials and paints, including
irreplaceable buildings, statues, and
sculptures that are part of our nation's
cultural heritage.
Pollution control: prevention,
technology and innovation
• Use fuels that contain fewer impurities (low
Sulfur coal and oil)
• Increase efficiency and conservation
• Control Sulfur and Nitrogen Oxide emissions
• Use pollution control devices that remove
particulate matter and other compounds after
combustion(fabric filters, electrostatic
precipitators, and scrubbers)
Scrubber
Electrostatic Precipitator
Innovative Pollution control
• Reduce the amount of gasoline spilled at gas
stations
• Restrict the evaporation of dry-cleaning fluid
• Reduction in the use of wood-burning stoves
• Reduce the number of bakeries in certain
areas (rising bread contains VOCs)
• Restricting automobile use
• Expand public transportation, carpool lanes
• Allowance for factories and S emissions
Stratospheric Ozone Layer
• Ozone in the stratosphere forms a necessary
protective shield against radiation from the
sun
• UV-A passes through the atmosphere w/o
being absorbed and contributes to skin cancer
• UV-B and UV-C have enough energy to cause
significant damage to the tissues and DNA of
living organisms
• The ozone layer absorbs 99% of UV-B and UVC
Tropospheric vs Stratospheric Ozone
• Tropospheric Ozone
• Ground level ozone
• Acts as an air
pollutant that
damages lung tissue
and plants
• Living organisms do
not live in the
stratosphere so this
ozone is not harmful
to them
• Absorbs UV radiation
and shields the
surface below
Formation and Breakdown of
Stratospheric Ozone
• O2 + UV-C 2O
• O2 + O O3
• O3 + UV-B or UV-C O2 + O
Anthropogenic Contributions to Ozone
Destruction
• Chlorine acts as a catalyst and can break
down ozone.
• CFCs- chlorofluorocarbons, used in
refrigerants, and in aerosols, get released
into the atmosphere. When it reaches
the stratosphere, one atom of Cl can
catalyzes the breakdown of 100,000
ozone molecules.
Depletion of the Ozone Layer in
Antarctica
Ozone Hole
• Each year for the past few decades during the
Southern Hemisphere spring, chemical
reactions involving chlorine and bromine
cause ozone in the southern polar region to be
destroyed rapidly and severely. This depleted
region is known as the “ozone hole”.
• As ozone decreases, UV-B radiation increases,
this is harmful to cells and reduces
photosynthetic activity and neg. impacts
ecosystems.
Efforts to reduce ozone depletion
• 1987- Montreal Protocol on Substances that
Deplete the Ozone Later- required the
elimination of CFCs production and use by the
developed world by 1996. It also addresses 96
other ozone depleting compounds.
• As a result, the level of chlorine in the
stratosphere has stabilized and the level of
ozone depletion should decrease in years to
come.
Indoor Air Pollution
• More than 3 billion people world wide use
wood, animal manure, or coal indoors for heat
and cooking.
• Usually there is no exhaust or ventilation so
indoor air pollution from CO and particulate
matter occurs.
• WHO estimates that indoor air pollution
causes more than 1.6 million deaths annually
in developing countries.
Some sources of indoor air pollution in
the developed world
Indoor air pollutants
• Asbestos- once used as an insulating material,
this fibrous silicate mineral causes lung cancer
and other respiratory diseases.
• Carbon Monoxide- CO- very dangerous indoor air
pollutant, present as a result of malfunctioning
exhaust systems on household heaters. When CO
builds up in a house, it binds with hemoglobin
leading to oxygen deprivation and death.
• Radon-radioactive gas that seeps into homes
through cracked foundations or soil. Second
leading cause lung cancer.
• VOCs- used in building materials, furniture,
glues, and paints. Formaldehyde is used in
particle board, carpet glue, pressed wood, and
in many places in new homes. Causes
irritation to the eyes and nose, breathing
difficulty, and asthma. Has been shown to
cause cancer in lab animals. Detergents, drycleaning fluids, deodorizers and solvents
contain VOCs that are released over time.
• Sick Building Syndrome- caused by products
made with synthetic materials and glue and
place in new buildings w/o proper ventilation.