Air PollutionAir Pollution

i

Exosphere

Thermosphere

Mesosphere

Stratosphere

Troposphere

Primary pollutants:Primary pollutants: are mixed vertically and horizontally and are 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 the while 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

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)

OzoneOzoneOzone is formed by the action of sunlight on carbon-based Ozone is formed by the action of sunlight on carbon-based chemicals known as hydrocarbons, acting in combination chemicals 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 body Ozone reacts chemically ("oxidizes") with internal body tissues that it comes in contact with, such as those in the tissues that it comes in contact with, such as those in the lung. Ozone (O3) in the troposphere causes more damage lung. Ozone (O3) in the troposphere causes more damage to plants than all other air pollutants combined. to plants than all other air pollutants combined.

SOSO2 2

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 fuel oxides (SOx ). These gases are formed when fuel containing sulfur (mainly coal and oil) is burned, and containing sulfur (mainly coal and oil) is burned, and during metal smelting and other industrial processes.during metal smelting and other industrial processes.

The major health concerns associated with exposure to The 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, and respiratory illness, alterations in pulmonary defenses, and aggravation of existing cardiovascular disease. aggravation of existing cardiovascular disease.

SOSO22 Emissions Emissions

LeadLead In the past, motor vehicles were the biggest In the past, motor vehicles were the biggest source of lead. But since leaded gasoline has source of lead. But since leaded gasoline has been phased out, lead emissions have decreased by about been phased out, lead emissions have decreased by about 98 percent. Today, metal processing is the biggest source 98 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 as organs. It may cause neurological impairments such as seizures, mental retardation and behavioral disorders. Even seizures, mental retardation and behavioral disorders. Even at low doses, lead is associated with damage to the nervous at low doses, lead is associated with damage to the nervous systems of fetuses and young children, resulting in lowered systems of fetuses and young children, resulting in lowered IQ and learning problems. IQ and learning problems.

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 certain matter floating around in the atmosphere, such as certain types 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.

NONO2 2 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 form gases called nitrogen oxides (NOx). These gases form when fuel is burned at high temperatures, and come when fuel is burned at high temperatures, and come principally from motor vehicle exhaust and stationary principally from motor vehicle exhaust and stationary sources 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.

Carbon MonoxideCarbon Monoxide Carbon MonoxideCarbon Monoxide is produced by the is produced by the incomplete combustion of the fossil fuels incomplete 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.

When When carbon monoxide is present in the air you breath into carbon 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 in carbon monoxide attaches to red blood cells in place of oxygen.place of oxygen.

Smog (smoke+fog)Smog (smoke+fog)

The Four Most Dangerous The Four Most Dangerous Indoor Air PollutantsIndoor Air Pollutants

1.1. cigarette smokecigarette smoke

2.2. FormaldehydeFormaldehyde

3.3. AsbestosAsbestos

4.4. radioactive radon-222 gas radioactive radon-222 gas

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 and Low levels of exposure can irritate the eyes, nose and throat, cause skin problems, serious breathing problems throat, 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.

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 and Health Effects: No immediate symptoms. Chest and abdominal cancers and lung diseases. Smokers are at abdominal cancers and lung diseases. Smokers are at higher risk of developing asbestos-induced lung cancer.higher risk of developing asbestos-induced lung cancer.

RADONRADON Sources: Earth, uranium and rock beneath home; well Sources: Earth, uranium and rock beneath home; well water; building materials.water; building materials.

Health Effects: No immediate symptoms. Estimated to Health Effects: No immediate symptoms. Estimated to cause about 10% of lung cancer deaths. Smokers are at cause 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.

Radon-222 can enter the house by diffusionRadon-222 can enter the house by diffusion from soil and by emanation from building from soil and by emanation from building materials, 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)

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.

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

Acid Deposition:Acid Deposition: the falling of acids and acid-forming the falling of acids and acid-forming compounds from the atmosphere to earth’s surface. Acid compounds from the atmosphere to earth’s surface. Acid deposition is commonly known as deposition 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-forming only 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

How to reduce acid depositionHow to reduce acid deposition

1.1. Reduce energy use and thus air pollution by improving Reduce energy use and thus air pollution by improving energy efficiencyenergy efficiency

2.2. Switch from coal to cleaner burning natural gas and Switch 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 from Remove SO2, particulates, and nitrogen oxides from smokestack gasessmokestack gases

6.6. Remove nitrogen oxides from motor vehicle exhaustRemove nitrogen oxides from motor vehicle exhaust

Sick BuildingSick BuildingA building is considered “sick” when at A building is considered “sick” when at

least 20% of its occupants suffer persistent least 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 million At least 17% of the 4 million commercial buildings in the U.S. are considered commercial buildings in the U.S. are considered “sick”.“sick”.

OzoneOzoneMost ozone (about 90%) Most ozone (about 90%) exists in the stratosphere, exists in the stratosphere, in a layer between 10 and in a layer between 10 and 50km above the surface of 50km above the surface of the earth. This ozone layer the earth. This ozone layer performs the essential performs the essential task of filtering out most task of filtering out most of the sun's biologically of the sun's biologically harmful ultraviolet (UV-harmful ultraviolet (UV-B) radiation. B) radiation.

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 15 stratospheric ozone has been depleted over the last 15

years at certain times of the year. This is mainly due to years at certain times of the year. This is mainly due to

the release of manmade chemicals containing chlorine the release of manmade chemicals containing chlorine such as CFC's (ChloroFluoroCarbons), but also compounds such as CFC's (ChloroFluoroCarbons), but also compounds containing bromine, other related halogen compounds and containing bromine, other related halogen compounds and also nitrogen oxides (NOx). also nitrogen oxides (NOx).

CFC’sCFC’s CFC's are chemicals that can be used in CFC'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 spray conditioning and in products in spray cans. CFC's rise into the air going into a layer called the cans. CFC's rise into the air going into a layer called the stratosphere. When this happens, the CFC's take part in stratosphere. When this happens, the CFC's take part in chemical reactions that can destroy parts of the ozone chemical 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.

Ozone HoleOzone Hole

1979 19981979 1998

The Earth is kept warm by it's atmosphere, which The Earth is kept warm by it's atmosphere, which acts rather like a woolly coat - without it, the acts rather like a woolly coat - without it, the average surface temperature would be about -18 average surface temperature would be about -18 degrees Centigrade. Heat from the sun passes degrees Centigrade. Heat from the sun passes through the atmosphere, warming it up. As the through the atmosphere, warming it up. As the Earth warms up, it emits heat. Some of this heat is Earth warms up, it emits heat. Some of this heat is trapped by the atmosphere, but the rest escapes into trapped by the atmosphere, but the rest escapes into space. The so-called "greenhouse gases" make the space. The so-called "greenhouse gases" make the atmosphere trap more of this radiation, so it atmosphere trap more of this radiation, so it gradually warms up more than it should, like a gradually warms up more than it should, like a greenhouse.greenhouse.

Greenhouse EffectGreenhouse Effect

Greenhouse Greenhouse EffectEffect

Greenhouse Effect Ozone Shield

Where in the atmosphere does it occur?

Troposphere Stratosphere

What process occurs? Traps heat near the earth’s surface

Filters ultraviolet (UV) radiation from the sun

What natural gases are involved?

Water(H2O), carbon dioxide(CO2), methane(CH4)

Oxygen(O2), ozone(O3)

What are important human inputs?

Carbon dioxide(CO2), methane (CH4), chlorofluorocarbons (CFCs), nitrous oxide(N2O)

Chlorofluorocarbons (CFCs), halons, carbon tetrachlorine, methyl choloroform (stable), halogen-containing gases

What problems result? Global warming Ozone depletion

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 atmosphere oxygen. 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 dioxide fossil fuels. Other natural sources of carbon dioxide include volcanic eruptions, decay of dead plant and animal include volcanic eruptions, decay of dead plant and animal matter, evaporation from the oceans and respiration matter, evaporation from the oceans and respiration (breathing). (breathing).

MethaneMethaneMethane is a greenhouse gas that is creating a serious Methane is a greenhouse gas that is creating a serious problem for global warming. Methane gases are very problem for global warming. Methane gases are very potent when trapping infrared heat in the atmosphere, potent when trapping infrared heat in the atmosphere, because one molecule of methane can trap infrared heat because one molecule of methane can trap infrared heat twenty times more than carbon dioxide. twenty times more than carbon dioxide.

Methane the second most importantMethane the second most importantgreenhouse gas is mostly produced greenhouse gas is mostly produced by the digestive system of cows. by the digestive system of cows.

AsthmaAsthma Smog and particles certainly Smog and particles certainly trigger attacks in some people trigger attacks in some people who already have asthma. For who already have asthma. For a long time it was thought a long time it was thought thatthat air pollution could not cause air pollution could not cause asthma to develop in asthma to develop in previously healthy people. Some recent previously healthy people. Some recent experiments challenge this belief. Scientists have shown experiments challenge this belief. Scientists have shown that people exposed to ozone or nitrogen dioxide are more that people exposed to ozone or nitrogen dioxide are more likely to react to allergens such as grass pollens and likely to react to allergens such as grass pollens and housedust mites than those who are not exposed. Thus a housedust mites than those who are not exposed. Thus a combination of air pollution and allergens could cause combination of air pollution and allergens could cause some cases of asthma. some cases of asthma.

Lung CancerLung CancerLung cancer is more common in cities Lung 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 by 90% of lung cancers are caused by smoking cigarettes. A radioactive gas smoking cigarettes. A radioactive gas called radon is thought to cause about called radon is thought to cause about 7% of lung cancers in North America. 7% of lung cancers in North America.

87% of lung cancer cases are caused by smoking. 12 87% 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-job Another leading cause of lung cancer is on-the-job exposure to cancer-causing substances or carcinogens. exposure to cancer-causing substances or carcinogens.

Air pollution can make you Air pollution can make you sick. It can cause burning eyes sick. It can cause burning eyes and nose and an itchy, irritated and nose and an itchy, irritated throat, as well as trouble in throat, as well as trouble in breathing. Some chemicals breathing. Some chemicals found in polluted air cause found in polluted air cause cancer, birth defects, brain and cancer, birth defects, brain and nerve damage and long-term nerve damage and long-term injury to the lungs and injury to the lungs and breathing passages. Some air breathing passages. Some air pollutants are so dangerous pollutants are so dangerous that accidental releases can that accidental releases can cause serious injury or even cause serious injury or even death.death.

According to the U.S. Environmental Protection Agency's According 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 criteria report, there have been significant reductions in all 6 criteria pollutants and reductions are expected to continue. pollutants and reductions are expected to continue.

The 1990 Clean Air ActThe 1990 Clean Air ActUnder this law, EPA sets limits on how much of a pollutant Under this law, EPA sets limits on how much of a pollutant can be in the air anywhere in the United States. This can be in the air anywhere in the United States. This ensures that all Americans have the same basic health and ensures that all Americans have the same basic health and environmental protections. The law allows individual states environmental protections. The law allows individual states to have stronger pollution controls, but states are not to have stronger pollution controls, but states are not allowed to have weaker pollution controls than those set allowed to have weaker pollution controls than those set for the whole country. for the whole country.

Chapter 19: Global Warming and Ozone Loss

The Greenhouse effect• In the Greenhouse effect,

certain gases in the atmosphere trap heat in the troposphere (lower atmosphere).

• If the atmospheric concentrations of these gases rise and arent removed by other processes, the average temp of the lower atmosphere will gradually increase.

Greenhouse gases• The major greenhouse

gases are water vapor (H20), carbon dioxide (C20), ozone (o3), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs), and a recently identified perfluorocarbons (PFCs)

• These gases remain in the atmosphere for 2,000-50,000 years.

• The two predominant gases are water vapor (hyrologic cycle) and carbon dioxide (global carbon cycle)

Global warming

• Measured atmospheric levels of certain greenhouse gases have risen substantially in recent decades and are projected to enhance the earth’s natural greenhouse effect, a phenomenon called global warming

• Most of the increased levels of these greenhouse gases since 1958 have been caused by human activities such as burning fossil fuels, agricultue, deforestation, and use of CFCs.

• 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

• Chloroflurocarbons (CFCs): – Contribute to global warming in the troposphere

and also deplete ozone in the stratosphere– Main sources are leaking ACs and fridges,

evaporation of industrial solvents, production of plastic foams, and aerosol propellants

– Trap 1,500- 7,000 times as much heat per molecule as CO2 while they are in the troposphere.

• Methane (CH4): – Accounts for about 20% of the overall warming

effect– Produced when anaerobic bacteria break down dead

organic matter in moist places that lack oxygen.– Stays in the troposphere for 9-15 years– Each CH4 molecule traps 20 times as much heat as

a CO2 molecule

• 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-fighting catalytic converters on motor vehicles, and the breakdown of nitrogen fertilizers in soil, livestock wastes, and nitrate-contaminated groundwater.

– Stays in the troposphere about 120 years. – About 200 times as much heat per molecule as CO2

• According to EPA, emission of greenhouse gases by the US rose by 20% between 1990 and 1996. Energy related activities accounted for about 86% of these emissions in 1996, mostly through burning fossil fuels.

• The atmospheric concentrations of CO2 and other greenhouse gases are projected to double from preindustrial levels sometimes during the next century and then continue to rise

The Earth’s past temperatures

• Since 1860, mean global temperature after correcting for excess 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 warmest years occurred between 1979 and 1998, with 1990, 1995, 1997, and 1998 being the four hottest years.

Future global warming and its effects

• According to the latest climate models, the earth’s mean surface temperature should rise 1- 3.5 degrees celsius between 1990 and 2100.

• Model projects that once the climate changes, it will continue for hundreds of years.

• According to the models, the northern hemisphere should warm more and faster than the southern hemisphere because the latter has more heat- absorbing ocean than land and because water cools more slowly than land.

How Earth’s climate is affected by various factors

• Solar output: ups and downs in solar output can temporarily warm or cool the earth and thus affect the projections of climate models.– Two studies showed that the

projected warming power of greenhouse gases should outweigh the climatic influence of the sun over at least the next 50 years.

• Oceans: the oceans might amplify global warming by releasing more CO2 into the atmosphere or might dampen it by absorbing more heat. The oceans currently help moderate tropospheric temperature by removing about 29% of the excess CO2 pumped into the atmosphere

• Water vapor content and clouds: changes in the atmosphere’s water vapor content and the amount and types of cloud cover also affect climate. Warmer temperatures would increase evaporation and the water-holding capacity of the air and create more clouds. Significant increase in the water vapor, a potent greenhouse gas, could enhance warming (positive feedback).

• Polar ice: the ability of the earth’s surface to reflect light is called its albedo. Because of their albedo, light-colored Greenland and Antarctic ice sheets act like enormous mirrors, reflecting sunlight back into space. If warmer temperatures melted some of this ice and exposed darker ground or ocean, more sunlight would be absorbed and warming would be accelerated.

• Air pollution: pollutants in the lower troposphere can either warm or cool the air depending on the reflectivity of the underlying surface.

• It is hypothesized that SO2 and tiny particles in the troposphere attract enough water molecules to form condensation nuclei, which leads to increased cloud formation

Some possible effects of a warmer world

• Food production: a warmer global climate could increase food production in 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 and location of many of the worlds forests

Continued…• Sea levels: in a warmer world, sea levels

are expected to rise, primarily because ocean water expands when heated and because some land-based glacial ice will melt

• Weather extremes: as more heat is retained in the earth’s climate system, more air will move across the earth’s surface.

• Human health: global warming would bring more heat waves, which would double or triple heat-related deaths among the elderly and people with heart disease; it would also increase suffering from respiratory ailments such as asthma and bronchitis.

Solutions: dealing with global warming

• Stabilizing the Co2 levels at the currect level would require reducing current global CO2 emissions by 66-83%.

• Increased use of nuclear power to reduce the amount of CO2 per unit of electricity as coal

• Using natural gas could help make the 40 to 50 year transition to an age of energy efficiency and renewable energy.

Ozone depletion• In a band of the stratosphere 17- 26 kms above

the earth’s surface, oxygen is continually converted to ozone and back to oxygen by a sequence of reactions initiated by UV radiation from the sun.

• UV radiation reaching the stratosphere consists of three bands: A, B, and C. The ozone layer blocks out nearly all of the highest- energy and biologically damaging UV-B band.

• Ozone depletion by certain chlorine- and bromine- containing chemicals emitted into the atmosphere by human activities is a serious long-term threat to human health, animal life, and the sunlight drive promary producers that support the earth’s food chains.

• CFCs released into the air rise slowly into the stratosphere. There, under the influence of high energy UV radiation, they break down and release highly reactive chlorine atoms, which speed up the breakdown of highly reactive ozone into O2 and O. This causes ozone to be destroyed faster than it is formed.

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 to pre- 1950 recovery levels.

• Substitutes are already available for most uses of CFCs. – Hydochlorofluorocarbons (HCFCs) contain

fewer chlorine atoms per molecule than CFCs• Because of their shorter lifetimes in the

stratosphere, these compounds should have only about 2.5% of the ozone depleting potential of CFCs.