Post on 30-May-2018
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Air PollutionAir PollutionAPES – Period 5APES – Period 5
Jane Kim
Janet Hong
Lynn Yi
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ExosphereThermosphere
Mesosphere
Stratosphere
Troposphere
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Primary pollutants:Primary pollutants: are mixed vertically and horizontally andare mixed vertically and horizontally and
are dispersed and diluted by the churning air in the troposphere.are dispersed and diluted by the churning air in the troposphere.
Ex: CO, COEx: CO, CO22, SO, SO22, NO, NO, NO, NO22, most hydrocarbons, and most, most hydrocarbons, and most
suspended particlessuspended particles
Secondary pollutants:Secondary pollutants: while in the troposphere, some of thewhile in the troposphere, some of the
primary pollutants may react with one another or with the basic primary pollutants may react with one another or with the basic
compounds of air.compounds of air.
Ex: SOEx: SO33, HNO, HNO33, H, H22SOSO44, H, H22OO22, O, O33, and PANs, and PANs
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Six Principal PollutantsSix Principal Pollutants
- Carbon Monoxide (CO)- Carbon Monoxide (CO)
- Lead (Pb)- Lead (Pb)
- Nitrogen Dioxide (NO2)- Nitrogen Dioxide (NO2)
- Ozone (O3)- Ozone (O3)
- Particulate Matter (PM-10)- Particulate Matter (PM-10)
- Sulfur Dioxide (SO2)- Sulfur Dioxide (SO2)
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OzoneOzoneOzone is formed by the action of sunlight on carbon-basedOzone is formed by the action of sunlight on carbon-based
chemicals known as hydrocarbons, acting in combinationchemicals known as hydrocarbons, acting in combination
with a group of air pollutants called oxides of nitrogen.with a group of air pollutants called oxides of nitrogen.
Ozone reacts chemically ("oxidizes") with internal bodyOzone reacts chemically ("oxidizes") with internal body
tissues that it comes in contact with, such as those in thetissues that it comes in contact with, such as those in the
lung. Ozone (O3) in the troposphere causes more damagelung. Ozone (O3) in the troposphere causes more damage
to plants than all other air pollutants combined.to plants than all other air pollutants combined.
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SOSO22
Sulfur dioxide belongs to the family of gases called sulfur Sulfur dioxide belongs to the family of gases called sulfur
oxides (SOx ). These gases are formed when fueloxides (SOx ). These gases are formed when fuel
containing sulfur (mainly coal and oil) is burned, andcontaining sulfur (mainly coal and oil) is burned, andduring metal smelting and other industrial processes.during metal smelting and other industrial processes.
The major health concerns associated with exposure toThe major health concerns associated with exposure to
high concentrations of SO2 include effects on breathing,high concentrations of SO2 include effects on breathing,
respiratory illness, alterations in pulmonary defenses, andrespiratory illness, alterations in pulmonary defenses, andaggravation of existing cardiovascular disease.aggravation of existing cardiovascular disease.
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SOSO22
EmissionsEmissions
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LeadLead In the past, motor vehicles were the biggestIn the past, motor vehicles were the biggest
source of lead. But since leaded gasoline hassource of lead. But since leaded gasoline has
been phased out, lead emissions have decreased by about been phased out, lead emissions have decreased by about98 percent. Today, metal processing is the biggest source98 percent. Today, metal processing is the biggest source
of atmospheric lead.of atmospheric lead.
Lead can harm the kidneys, liver, nervous system and other Lead can harm the kidneys, liver, nervous system and other organs. It may cause neurological impairments such asorgans. It may cause neurological impairments such as
seizures, mental retardation and behavioral disorders. Evenseizures, mental retardation and behavioral disorders. Even
at low doses, lead is associated with damage to the nervousat low doses, lead is associated with damage to the nervous
systems of fetuses and young children, resulting in loweredsystems of fetuses and young children, resulting in lowered
IQ and learning problems.IQ and learning problems.
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ParticulatesParticulatesParticulates is a general term used to describe tiny bits of Particulates is a general term used to describe tiny bits of
matter floating around in the atmosphere, such as certainmatter floating around in the atmosphere, such as certaintypes of smoke (like diesel smoke), fine ash and dust. Larger types of smoke (like diesel smoke), fine ash and dust. Larger
particles are caught by the hairs in your nose and your particles are caught by the hairs in your nose and your
breathing tubes, but smaller particles can get past these breathing tubes, but smaller particles can get past these
defenses and cause lots of trouble.defenses and cause lots of trouble.
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NONO22 Nitrogen dioxide belongs to a family of highly reactive Nitrogen dioxide belongs to a family of highly reactive
gases called nitrogen oxides (NOx). These gases formgases called nitrogen oxides (NOx). These gases form
when fuel is burned at high temperatures, and comewhen fuel is burned at high temperatures, and come
principally from motor vehicle exhaust and stationary principally from motor vehicle exhaust and stationarysources such as electric utilities and industrial boilers.sources such as electric utilities and industrial boilers.
Nitrogen dioxide can irritate the lungs and lower resistance Nitrogen dioxide can irritate the lungs and lower resistance
to respiratory infections such as influenza.to respiratory infections such as influenza.
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Carbon MonoxideCarbon Monoxide
Carbon MonoxideCarbon Monoxide is produced by theis produced by theincomplete combustion of the fossil fuelsincomplete combustion of the fossil fuels
– gas, oil, coal and wood used in boilers,– gas, oil, coal and wood used in boilers,
engines, oil burners, gas fires, water heaters,engines, oil burners, gas fires, water heaters,
solid fuel appliances and open fires.solid fuel appliances and open fires.
WhenWhen carbon monoxide is present in the air you breath intocarbon monoxide is present in the air you breath into
your lungs, it attaches itself to the hemoglobin.your lungs, it attaches itself to the hemoglobin.
The bondThe bond between hemoglobin and carbon monoxide is 250 between hemoglobin and carbon monoxide is 250
times stronger than oxygen.times stronger than oxygen.
In the lungsIn the lungs carbon monoxide attaches to red blood cells incarbon monoxide attaches to red blood cells in
place of oxygen. place of oxygen.
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Smog (smoke+fog)Smog (smoke+fog)
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The Four Most DangerousThe Four Most Dangerous
Indoor Air PollutantsIndoor Air Pollutants
2.2. cigarette smokecigarette smoke
3.3. FormaldehydeFormaldehyde
4.4.
AsbestosAsbestos
5.5. radioactive radon-222 gasradioactive radon-222 gas
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FormaldehydeFormaldehyde Formaldehyde is a colorless liquid or gas with a strong,Formaldehyde is a colorless liquid or gas with a strong,
distinctive odor. It is found in furniture, new carpets,distinctive odor. It is found in furniture, new carpets,
particle board, plywood, rubber cement and adhesives. particle board, plywood, rubber cement and adhesives.
Low levels of exposure can irritate the eyes, nose andLow levels of exposure can irritate the eyes, nose and
throat, cause skin problems, serious breathing problemsthroat, cause skin problems, serious breathing problems
and can increase your risk of certain kinds of cancer.and can increase your risk of certain kinds of cancer.
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ASBESTOSASBESTOS Sources: Deteriorating of damaged insulation, fire-Sources: Deteriorating of damaged insulation, fire-
proofing, or acoustical materials. proofing, or acoustical materials.
Health Effects: No immediate symptoms. Chest andHealth Effects: No immediate symptoms. Chest andabdominal cancers and lung diseases. Smokers are atabdominal cancers and lung diseases. Smokers are at
higher risk of developing asbestos-induced lung cancer.higher risk of developing asbestos-induced lung cancer.
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RADONRADON Sources: Earth, uranium and rock beneath home; wellSources: Earth, uranium and rock beneath home; well
water; building materials.water; building materials.
Health Effects: No immediate symptoms. Estimated toHealth Effects: No immediate symptoms. Estimated tocause about 10% of lung cancer deaths. Smokers are atcause about 10% of lung cancer deaths. Smokers are at
higher risk of developing radon-induced lung cancer.higher risk of developing radon-induced lung cancer.
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Radon-222 can enter the house by diffusionRadon-222 can enter the house by diffusion
from soil and by emanation from buildingfrom soil and by emanation from buildingmaterials, tap water and methane gas.materials, tap water and methane gas.
CharacteristicsCharacteristics- an odorless, tasteless, invisible gas that mixes with air - an odorless, tasteless, invisible gas that mixes with air
- chemically inert and essentially non-reactive- chemically inert and essentially non-reactive
- heaviest noble gas with highest melting and boiling point- heaviest noble gas with highest melting and boiling point
- highly soluble in non-polar solvents- highly soluble in non-polar solvents- moderately soluble in cold water - moderately soluble in cold water
- able to diffuse through rock and soil- able to diffuse through rock and soil
- decays by alpha particle emission (T 1/2 = 3.8 days)- decays by alpha particle emission (T 1/2 = 3.8 days)
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The largest source of "indoor air
pollution"- in our homes, our schools or
workplaces- is car and truck pollution.
Electric vehicles are sometimes referred
to as "zero-emission vehicles" because
they produce essentially no pollution
from the tailpipe or through fuel
evaporation. This is important, for it
means that the use of electric vehicles
could greatly reduce emissions of carbon monoxide and smog-forming
pollutants in cities with dirty air.
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Symptoms (IAP)Symptoms (IAP)As many as 20 million Americans suffer from:As many as 20 million Americans suffer from:
- chronic breathing problemschronic breathing problems
- dizzinessdizziness
- rashrash
- headachesheadaches
- sore throatsore throat
- sinussinus
- eye irritationeye irritation
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Acid Deposition:Acid Deposition: the falling of acids and acid-formingthe falling of acids and acid-forming
compounds from the atmosphere to earth’s surface. Acidcompounds from the atmosphere to earth’s surface. Acid
deposition is commonly known asdeposition is commonly known as acid rainacid rain, a term that refers, a term that refers
only to wet deposition of droplets of acids and acid-formingonly to wet deposition of droplets of acids and acid-forming
compoundscompounds
Effects of Acid rainEffects of Acid rain
- human respiratory disease (bronchitis and asthma)human respiratory disease (bronchitis and asthma)
- damages statues, buildings, metals, and car finishesdamages statues, buildings, metals, and car finishes
- depletion of calcium and magnesium ions in the soildepletion of calcium and magnesium ions in the soil
- damages treesdamages trees
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How to reduce acid depositionHow to reduce acid deposition
1.1. Reduce energy use and thus air pollution by improvingReduce energy use and thus air pollution by improving
energy efficiencyenergy efficiency
2.2. Switch from coal to cleaner burning natural gas andSwitch from coal to cleaner burning natural gas and
renewable energy resourcesrenewable energy resources
3.3. Remove sulfur from coal before it is burnedRemove sulfur from coal before it is burned
4.4. Burn low-sulfur coalBurn low-sulfur coal
5.5. Remove SO2, particulates, and nitrogen oxides fromRemove SO2, particulates, and nitrogen oxides from
smokestack gasessmokestack gases
6.6. Remove nitrogen oxides from motor vehicle exhaustRemove nitrogen oxides from motor vehicle exhaust
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Sick BuildingSick Building
A building is considered “sick” when atA building is considered “sick” when at
least 20% of its occupants suffer persistentleast 20% of its occupants suffer persistent
symptoms that disappear when they go outsidesymptoms that disappear when they go outside
At least 17% of the 4 millionAt least 17% of the 4 million
commercial buildings in the U.S. are consideredcommercial buildings in the U.S. are considered
“sick”.“sick”.
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OzoneOzoneMost ozone (about 90%)Most ozone (about 90%)
exists in the stratosphere,exists in the stratosphere,
in a layer between 10 andin a layer between 10 and
50km above the surface of 50km above the surface of the earth. This ozonethe earth. This ozone
layer performs thelayer performs the
essential task of filteringessential task of filtering
out most of the sun'sout most of the sun's biologically harmful biologically harmful
ultraviolet (UV-B)ultraviolet (UV-B)
radiation.radiation.
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Ozone HoleOzone Hole
Over Antarctica (and recently over the Arctic),Over Antarctica (and recently over the Arctic),
stratospheric ozone has been depleted over the last 15stratospheric ozone has been depleted over the last 15
years at certain times of the year. This is mainly due toyears at certain times of the year. This is mainly due to
the release of manmade chemicals containing chlorinethe release of manmade chemicals containing chlorine
such as CFC's (ChloroFluoroCarbons), but also compoundssuch as CFC's (ChloroFluoroCarbons), but also compounds
containing bromine, other related halogen compounds andcontaining bromine, other related halogen compounds and
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CFC’sCFC’s CFC's are chemicals that can be used inCFC's are chemicals that can be used in
the refrigerator to help keep food cold.the refrigerator to help keep food cold.
They can also be used in air-They can also be used in air-
conditioning and in products in sprayconditioning and in products in spraycans. CFC's rise into the air going into a layer called thecans. CFC's rise into the air going into a layer called the
stratosphere. When this happens, the CFC's take part instratosphere. When this happens, the CFC's take part in
chemical reactions that can destroy parts of the ozonechemical reactions that can destroy parts of the ozone
which protects us from the sun's dangerous ultraviolet rays.which protects us from the sun's dangerous ultraviolet rays.
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Ozone HoleOzone Hole
1979 19981979 1998
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The Earth is kept warm by it's atmosphere, whichThe Earth is kept warm by it's atmosphere, which
acts rather like a woolly coat - without it, theacts rather like a woolly coat - without it, the
average surface temperature would be about -18average surface temperature would be about -18
degrees Centigrade. Heat from the sun passesdegrees Centigrade. Heat from the sun passesthrough the atmosphere, warming it up. As thethrough the atmosphere, warming it up. As the
Earth warms up, it emits heat. Some of this heat isEarth warms up, it emits heat. Some of this heat is
trapped by the atmosphere, but the rest escapes intotrapped by the atmosphere, but the rest escapes into
space. The so-called "greenhouse gases" make thespace. The so-called "greenhouse gases" make theatmosphere trap more of this radiation, so itatmosphere trap more of this radiation, so it
gradually warms up more than it should, like agradually warms up more than it should, like a
greenhouse.greenhouse.
Greenhouse EffectGreenhouse Effect
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GreenhouseGreenhouse
EffectEffect
Ozone ShieldGreenhouse Effect
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Ozone depletionGlobal warmingWhat problems result?
Chlorofluorocarbons
(CFCs), halons, carbon
tetrachlorine, methyl
choloroform (stable),
halogen-containing gases
Carbon dioxide(CO2),
methane (CH4),
chlorofluorocarbons (CFCs),
nitrous oxide(N2O)
What are important
human inputs?
Oxygen(O2), ozone(O3)Water(H2O), carbon
dioxide(CO2
), methane(CH4
)
What natural gases are
involved?
Filters ultraviolet (UV)
radiation from the sun
Traps heat near the earth’s
surface
What process occurs?
StratosphereTroposphereWhere in the atmosphere
does it occur?
Ozone ShieldGreenhouse Effect
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Carbon DioxideCarbon DioxideCarbon dioxide is produced when any form of carbon or Carbon dioxide is produced when any form of carbon or
almost any carbon compound is burned in an excess of almost any carbon compound is burned in an excess of
oxygen. For example, it is released into the atmosphereoxygen. For example, it is released into the atmosphere
during natural forest fires and the man-made combustion of during natural forest fires and the man-made combustion of fossil fuels. Other natural sources of carbon dioxidefossil fuels. Other natural sources of carbon dioxide
include volcanic eruptions, decay of dead plant and animalinclude volcanic eruptions, decay of dead plant and animal
matter, evaporation from the oceans and respirationmatter, evaporation from the oceans and respiration
(breathing).(breathing).
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AsthmaAsthmaSmog and particles certainlySmog and particles certainly
trigger attacks in some peopletrigger attacks in some people
who already have asthma. For who already have asthma. For
a long time it was thoughta long time it was thoughtthatthat
air pollution could not causeair pollution could not cause
asthma to develop inasthma to develop in
previously healthy people. Some recent previously healthy people. Some recentexperiments challenge this belief. Scientists have shownexperiments challenge this belief. Scientists have shown
that people exposed to ozone or nitrogen dioxide are morethat people exposed to ozone or nitrogen dioxide are more
likely to react to allergens such as grass pollens andlikely to react to allergens such as grass pollens and
housedust mites than those who are not exposed. Thus ahousedust mites than those who are not exposed. Thus a
combination of air pollution and allergens could causecombination of air pollution and allergens could cause
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Lung Cancer Lung Cancer
Lung cancer is more common in citiesLung cancer is more common in cities
than in the country. We know that over than in the country. We know that over 90% of lung cancers are caused by90% of lung cancers are caused by
smoking cigarettes. A radioactive gassmoking cigarettes. A radioactive gas
called radon is thought to cause aboutcalled radon is thought to cause about
7% of lung cancers in North America.7% of lung cancers in North America.
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87% of lung cancer cases are caused by smoking. 1287% of lung cancer cases are caused by smoking. 12
percent of all lung cancer deaths are linked to radon. percent of all lung cancer deaths are linked to radon.
Another leading cause of lung cancer is on-the-jobAnother leading cause of lung cancer is on-the-job
exposure to cancer-causing substances or carcinogens.exposure to cancer-causing substances or carcinogens.
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Air pollution can make youAir pollution can make you
sick. It can cause burning eyessick. It can cause burning eyes
and nose and an itchy, irritatedand nose and an itchy, irritatedthroat, as well as trouble inthroat, as well as trouble in
breathing. Some chemicals breathing. Some chemicals
found in polluted air causefound in polluted air cause
cancer, birth defects, brain andcancer, birth defects, brain andnerve damage and long-termnerve damage and long-term
injury to the lungs andinjury to the lungs and
breathing passages. Some air breathing passages. Some air
pollutants are so dangerous pollutants are so dangerous
that accidental releases canthat accidental releases can
cause serious injury or evencause serious injury or even
death.death.
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According to the U.S. Environmental Protection Agency'sAccording to the U.S. Environmental Protection Agency's
(EPA) latest Ten-Year Air Quality and Emissions Trends(EPA) latest Ten-Year Air Quality and Emissions Trends
report, there have been significant reductions in all 6 criteriareport, there have been significant reductions in all 6 criteria
pollutants and reductions are expected to continue. pollutants and reductions are expected to continue.
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The 1990 Clean Air ActThe 1990 Clean Air ActUnder this law, EPA sets limits on how much of a pollutantUnder this law, EPA sets limits on how much of a pollutant
can be in the air anywhere in the United States. Thiscan be in the air anywhere in the United States. This
ensures that all Americans have the same basic health andensures that all Americans have the same basic health and
environmental protections. The law allows individual statesenvironmental protections. The law allows individual statesto have stronger pollution controls, but states are notto have stronger pollution controls, but states are not
allowed to have weaker pollution controls than those setallowed to have weaker pollution controls than those set
for the whole country.for the whole country.
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Chapter 19: Global
Warming and Ozone Loss
Jane S. Kim
Janet Hong
Lynn Yi
Period 5, APES
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The Greenhouse effect
• In the Greenhouseeffect, certain gases inthe atmosphere trapheat in the troposphere
(lower atmosphere).
• If the atmospheric
concentrations of thesegases rise and arentremoved by otherprocesses, the average
temp of the lower
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Global warming
• Measured atmospheric levels of certaingreenhouse gases have risensubstantially in recent decades and areprojected to enhance the earth’s naturalgreenhouse effect, a phenomenoncalled global warming
• Most of the increased levels of these
greenhouse gases since 1958 havebeen caused by human activities suchas burning fossil fuels, agricultue,deforestation, and use of CFCs.
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• Carbon dioxide (CO2):– Responsible for 50-60% of the global warming
from greenhouse gases produced by human
activites– Main sources are fossil fuel burning (70-75%)
and land clearing and burning (20-25%)
– Remains in atmosphere for 50-200 years
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• Chloroflurocarbons (CFCs):– Contribute to global warming in the
troposphere and also deplete ozone in thestratosphere
– Main sources are leaking ACs and fridges,evaporation of industrial solvents,production of plastic foams, and aerosolpropellants
– Trap 1,500- 7,000 times as much heat per
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• Methane (CH4):– Accounts for about 20% of the overall warming
effect
– Produced when anaerobic bacteria break downdead organic matter in moist places that lackoxygen.
– Stays in the troposphere for 9-15 years
– Each CH4 molecule traps 20 times as much
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• Nitrous oxide (N2O):– Can trap heat in the troposphere and also
deplete ozone in the stratosphere
– Released from nylon production, burning of
biomass and nitrogen-rich fuels, smog-fightingcatalytic converters on motor vehicles, and thebreakdown of nitrogen fertilizers in soil, livestockwastes, and nitrate-contaminated groundwater.
–Stays in the troposphere about 120 years.–
A di EPA i i f
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• According to EPA, emission of greenhouse gases by the US rose
by 20% between 1990 and 1996.Energy related activities accountedfor about 86% of these emissionsin 1996, mostly through burning
fossil fuels.
• The atmospheric concentrations of CO2 and other greenhouse gases
are projected to double frompreindustrial levels sometimesduring the next century and then
continue to rise
The Earth’s past
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The Earth s pasttemperatures
• Since 1860, mean globaltemperature after correcting forexcess heating over urban areas
has risen 0.3-0.6 degrees Celsius.• Temperature rose about 0.3
degrees between 1846 and 1997
• Since 1860, the thirteen warmestyears occurred between 1979 and1998, with 1990, 1995, 1997, and1998 being the four hottest years.
F t l b l i d it
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Future global warming and itseffects
• According to thelatest climatemodels, theearth’s mean
surfacetemperatureshould rise 1- 3.5degrees celsiusbetween 1990and 2100.
• Model projectsthat once theclimate changes,it will continue for
• According to themodels, thenorthernhemisphere
should warmmore and fasterthan the southernhemispherebecause the latterhas more heat-absorbing ocean
than land and
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How Earth’s climate is
affected by various factors
• Solar output: ups and downs in
solar output can temporarily warmor cool the earth and thus affectthe projections of climate models.
– Two studies showed that theprojected warming power of greenhouse gases should outweighthe climatic influence of the sun over
at least the next 50 years.
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• Oceans: the oceans mightamplify global warming byreleasing more CO2 into theatmosphere or might dampen it by
absorbing more heat. The oceanscurrently help moderatetropospheric temperature by
removing about 29% of the excess
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• Water vapor content andclouds: changes in the
atmosphere’s water vapor contentand the amount and types of cloudcover also affect climate. Warmertemperatures would increase
evaporation and the water-holdingcapacity of the air and create moreclouds. Significant increase in thewater vapor, a potent greenhouse
gas, could enhance warming
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• Polar ice: the ability of the earth’s
surface to reflect light is called itsalbedo. Because of their albedo, light-colored Greenland and Antarctic icesheets act like enormous mirrors,
reflecting sunlight back into space. If warmer temperatures melted some of this ice and exposed darker ground orocean, more sunlight would be
absorbed and warming would be
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• Air pollution: pollutants in the lowertroposphere can either warm or cool theair depending on the reflectivity of the
underlying surface.• It is hypothesized that SO2 and tiny
particles in the troposphere attractenough water molecules to form
condensation nuclei, which leads to
Some possible effects of a
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Some possible effects of awarmer world
• Food production: a warmer global
climate could increase food productionin some areas and lower it in others,depending on crop- growing capacity
and climate belts.• Water supply: global warming would
reduce water supply, shrinking or
completely drying up lakes, streams,and aquifers.
• Forests and biodiversity: global
warming would change the makeup
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Continued…
•Sea levels: in a warmer world, sealevels are expected to rise, primarilybecause ocean water expands whenheated and because some land-basedglacial ice will melt
• Weather extremes: as more heat isretained in the earth’s climate system,more air will move across the earth’ssurface.
• Human health: global warming wouldbring more heat waves, which woulddouble or triple heat-related deathsamong the elderly and people withheart disease; it would also increase
Solutions: dealing with global
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Solutions: dealing with globalwarming
• Stabilizing the Co2 levels at thecurrect level would requirereducing current global CO2emissions by 66-83%.
• Increased use of nuclear power toreduce the amount of CO2 per unitof electricity as coal
• Using natural gas could help makethe 40 to 50 year transition to anage of energy efficiency and
renewable energy.
O d l ti
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Ozone depletion• In a band of the stratosphere 17- 26 kms
above the earth’s surface, oxygen iscontinually converted to ozone and back tooxygen by a sequence of reactions initiatedby UV radiation from the sun.
• UV radiation reaching the stratosphereconsists of three bands: A, B, and C. Theozone layer blocks out nearly all of thehighest- energy and biologically damaging
UV-B band.• Ozone depletion by certain chlorine- and
bromine- containing chemicals emitted intothe atmosphere by human activities is a
serious long-term threat to human health,
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• CFCs released into the air rise slowly into thestratosphere. There, under the influence of high energy UV radiation, they break downand release highly reactive chlorine atoms,which speed up the breakdown of highlyreactive ozone into O2 and O. This causesozone to be destroyed faster than it is
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Solutions: protecting the
ozone layer• It will take another 50-60 years for the
ozone layer to return to 1975 levels
and another 100- 200 years to return topre- 1950 recovery levels.
• Substitutes are already available formost uses of CFCs.
– Hydochlorofluorocarbons (HCFCs) containfewer chlorine atoms per molecule thanCFCs•Because of their shorter lifetimes in the