Air Unit7

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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

http://www.nobel.se/chemistry/educational/poster/1995/2.gif

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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

Air Unit7

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