AIR POLLUTION CONTROL L 11

LL--1111OZONE DEPLETIONOZONE DEPLETION

Air Pollution and ControlAir Pollution and Control

(Elective(Elective--I)I)

Earth’s AtmosphereEarth’s Atmosphere

22Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

The ozone layerThe ozone layer

•• Ozone is an unstable gasOzone is an unstable gas

•• It rapidly breaks downIt rapidly breaks down

•• The ozone layer is only a The ozone layer is only a few cm thickfew cm thick

•• If the rate of breakdown is faster than If the rate of breakdown is faster than the rate of formation the ozone layer the rate of formation the ozone layer thinsthins

•• This could develop into holeThis could develop into hole

•• An ozone hole was first observed over An ozone hole was first observed over the Antarctic in 1985the Antarctic in 1985


TheThe DiscoveryDiscovery

Team who discovered the hole 1985. From left: Joe Farman, Brian Gardiner, and Jonathan Shanklin

British Atlantic Survey Research station, Holly Bay, Antarctic coast

•• In 1985, using satellites, balloons, and In 1985, using satellites, balloons, and surface stations, a team of researchers had surface stations, a team of researchers had discovered a balding patch of ozone in the discovered a balding patch of ozone in the upper stratosphere, the size of the United upper stratosphere, the size of the United States, over Antarctica. States, over Antarctica.


Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET 55

What is ozone?What is ozone?•• Ozone forms a layer Ozone forms a layer

in the stratosphere, in the stratosphere, thinnest in the tropics thinnest in the tropics (around the equator) (around the equator) and denser towards and denser towards the polesthe poles

•• measured in Dobson measured in Dobson units (DU)units (DU)

•• ~260 DU near the ~260 DU near the tropicstropics 66Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

What is a Dobson unit?What is a Dobson unit?

•• 1 Dobson Unit 1 Dobson Unit (DU) is defined to (DU) is defined to be 0.01 mm be 0.01 mm thickness at STP thickness at STP -- (0(000C and 1 C and 1 atmos pressure). atmos pressure).

•• A slab 3mm thick A slab 3mm thick corresponds to corresponds to 300 DU300 DU 77Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

How is ozone formed?How is ozone formed?UV radiation strikes the O2 molecule and splits it, atomic oxygen associates itself with another O2

molecule – simplistic version


How ironic . . .How ironic . . .•• At ground level, ozone is a health At ground level, ozone is a health

hazardhazard--major constituent of major constituent of photochemical smogphotochemical smog

•• However, in the stratosphere, we However, in the stratosphere, we could not survive without it. could not survive without it.

•• It absorbs potentially harmful ultraIt absorbs potentially harmful ultra--violet (UV violet (UV –– 240240--320nm harmful) 320nm harmful) radiation radiation

•• Protects from skin cancer, etcProtects from skin cancer, etc 99

Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

The ozone layer is in the stratosphere The ozone layer is in the stratosphere

Good uphigh!

Badnearby!

“Chapman Reactions”“Chapman Reactions”

•• Ozone is formed by:Ozone is formed by:OO22 + + hvhv --> O + O > O + O (1)(1)

•• Ozone can reform resulting in no net loss of Ozone can reform resulting in no net loss of ozone: ozone:

OO33 + + hvhv --> O> O22 + O + O (3)(3)O + OO + O22 --> O> O33 (2)(2)

•• Ozone is also destroyed by the following Ozone is also destroyed by the following reaction: reaction:

O + OO + O33 --> O> O22 + O+ O22 (4)(4)1111

Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

Comparison of reactionsComparison of reactions

•• Reaction (2) slower with increasing Reaction (2) slower with increasing altitudealtitude

•• Reaction (3) faster with increasing altitudeReaction (3) faster with increasing altitude

•• Lower in stratosphere, atmosphere Lower in stratosphere, atmosphere denser, UV absorption increases denser, UV absorption increases –– ozone ozone peaks 20kmpeaks 20km

•• Closer to surface, UV level decreases, Closer to surface, UV level decreases, ozone decreasesozone decreases


•Ozone is a triatomic form of oxygen (O3) found in Earth’s upper and lower atmosphere. •The ozone layer, situated in the stratosphere about 15 to 30 km above the earth's surface. •Ozone protects living organisms by absorbing harmful ultraviolet radiation (UVB) from the sun.

The ozone layer



ultraviolet A (long-wave) and ultraviolet B (shortwave) rays

• The ozone layer is being destroyed by CFCs and other substances.

• Ozone depletion progressing globally except in the tropical zone.

• Chlorofluoro carbons (CFC’s) and other halogenated hydrocarbons contribute to the destruction of stratospheric ozone.

• Just one chlorine and bromine atom can catalyze the destruction of 100,000 ozone molecules Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

1515

What are CFCs?What are CFCs?•• Used as propellants in aerosol spray Used as propellants in aerosol spray

canscans

•• Used as refrigerants in fridges, Used as refrigerants in fridges, freezers and air conditioning unitsfreezers and air conditioning units



The ozone depletion processThe ozone depletion process


Too much ultraToo much ultra--violet light can result inviolet light can result in::

• Skin cancer• Eye damage such as cataracts• Immune system damage• Reduction in phytoplankton• Damage to the DNA in various life-forms • Possibly other things too that we don't

know about at the moment


Effects on PlantsPhysiological and developmental processes of plants are affected by UVB radiation, even by the amount of UVB in present-day sunlight.


•• Effects on Marine EcosystemsEffects on Marine Ecosystems

•• Phytoplankton form the foundation of aquatic Phytoplankton form the foundation of aquatic food webs. food webs.

•• Exposure to solar UVB radiation has been Exposure to solar UVB radiation has been shown to affect both orientation mechanisms shown to affect both orientation mechanisms and motility in phytoplankton, resulting in and motility in phytoplankton, resulting in reduced survival rates for these organisms.reduced survival rates for these organisms.


•• Effects on Biogeochemical CyclesEffects on Biogeochemical Cycles

•• Increases in solar UV radiation could affect Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical terrestrial and aquatic biogeochemical cycles, thus altering both sources and sinks cycles, thus altering both sources and sinks of greenhouse and chemicallyof greenhouse and chemically--important important trace gases.trace gases.

•• e.g., carbon dioxide (COe.g., carbon dioxide (CO22), carbon monoxide ), carbon monoxide (CO), carbonyl sulfide (COS) and possibly other (CO), carbonyl sulfide (COS) and possibly other gases, including ozone. gases, including ozone.

•• These potential changes would contribute to These potential changes would contribute to biospherebiosphere--atmosphere feedbacks that attenuate atmosphere feedbacks that attenuate or reinforce the atmospheric buildup of these or reinforce the atmospheric buildup of these gases.gases. Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

2323

•• Effects on MaterialsEffects on Materials

•• Synthetic polymers, Synthetic polymers, naturally occurring naturally occurring biopolymersbiopolymers, as well as some other materials , as well as some other materials of commercial interest are adversely affected by of commercial interest are adversely affected by solar UV radiation.solar UV radiation.

•• Today's materials are somewhat protected Today's materials are somewhat protected from UVB by special additives. from UVB by special additives.

•• Therefore, any increase in solar UVB levels will Therefore, any increase in solar UVB levels will therefore accelerate their breakdown, limiting therefore accelerate their breakdown, limiting the length of time for which they are useful the length of time for which they are useful outdoors.outdoors.


Immune Suppression•Scientists have found that overexposure to UV radiation may suppress proper functioning of the body’s immune system and the skin’s natural defenses.• For example, the skin normally mounts a defense against foreign invaders such as cancers and infections.


•• But overexposure to UV radiation can But overexposure to UV radiation can weaken the immune system, reducing weaken the immune system, reducing the skin’s ability to protect against the skin’s ability to protect against these invaders.these invaders.


Effects on Human HealthEffects on Human Health

Skin cancerSkin cancer

-- Unprotected exposure Unprotected exposure to UV radiation is the to UV radiation is the most preventable risk most preventable risk factor for skin cancer.factor for skin cancer.

malignant

Non-malignant


Over ExposureOver Exposure•• Accelerate aging of skin due high Accelerate aging of skin due high

exposure exposure --The face, hands, The face, hands, forearms, and the “V” of the neck forearms, and the “V” of the neck are especially susceptible to this are especially susceptible to this type of lesion.type of lesion.


•• CataractCataract-- Cataracts are a Cataracts are a form of eye form of eye

damage in which a loss of damage in which a loss of transparency in the lens of the eye transparency in the lens of the eye clouds vision.clouds vision.

-- If left untreated, cataracts can lead If left untreated, cataracts can lead to blindness. to blindness.

-- Research has shown that UV Research has shown that UV radiation increases the likelihood of radiation increases the likelihood of certain cataracts.certain cataracts. Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET

2929

What can be done?What can be done?

•• Reduce the use of CFCsReduce the use of CFCs

•• They are already banned in aerosols They are already banned in aerosols (1987)(1987)

•• BUT they are still used as refrigerantsBUT they are still used as refrigerants

•• Recycle fridges and air conditioning Recycle fridges and air conditioning plantsplants


Skin ProtectionSkin Protection

•• Protect the skin against the solar radiation Protect the skin against the solar radiation using skin creams with SPFusing skin creams with SPF

•• Use lip balm with SPFUse lip balm with SPF

•• Cover upCover up


ProtectionProtection

•• Sunglasses with 100% UV Sunglasses with 100% UV blockblock

•• Wrap around sunglassesWrap around sunglasses

•• Eye protection for childrenEye protection for children

•• HatsHats


What Is Being Done to Counter the Effects What Is Being Done to Counter the Effects of Ozone Depletion?of Ozone Depletion?

•• Montreal ProtocolMontreal Protocol (adopted in 1987)(adopted in 1987) –– panel panel of experts was formed to investigate substances of experts was formed to investigate substances responsible for hole formationresponsible for hole formation

•• Established policies that prevent future use of Established policies that prevent future use of certain types of chemicals certain types of chemicals

•• Stipulated that the production and Stipulated that the production and consumption of compounds contributing consumption of compounds contributing towards depletion of ozone in the stratosphere towards depletion of ozone in the stratosphere were to be phased out by the year 2000 (2005 were to be phased out by the year 2000 (2005 for for methylchloroformmethylchloroform))


The current situationThe current situation•• The holes developing over the pole suggest The holes developing over the pole suggest

that they may be show an improvementthat they may be show an improvement

•• BUT CFC molecules take 30 years to rise up BUT CFC molecules take 30 years to rise up to the stratosphereto the stratosphere

•• The chlorine radicals last a long timeThe chlorine radicals last a long time

•• The peak ozone damage was supposed to The peak ozone damage was supposed to be in 2000be in 2000

•• Damage could go on another 50 yearsDamage could go on another 50 years

© 2007 Paul Billiet ODWS

Signs of Recovery???Signs of Recovery???

There have been some signs of recoveryThere have been some signs of recovery

•• 1997 satellite showed a decline of 1997 satellite showed a decline of several known ozoneseveral known ozone--depleting gasesdepleting gases

•• Satellite images show some slowing Satellite images show some slowing down of ozone lossdown of ozone loss

However….However….

Recovery is slow

Antarctica - Dec. 2005


Objective QuestionsObjective QuestionsQ1. Ozone hole was first observed in ____.Q1. Ozone hole was first observed in ____.

Q2. The ozone layer, situated in the stratosphere Q2. The ozone layer, situated in the stratosphere about __________km above the earth's about __________km above the earth's surface. surface.

Q3. _______ is responsible for ozone depletion.Q3. _______ is responsible for ozone depletion.

Q4. ___________ protocol was first step towards Q4. ___________ protocol was first step towards reducing use of CFCs.reducing use of CFCs.

Q5.Breaking of ozone molecule takes place in Q5.Breaking of ozone molecule takes place in presence of ________________.presence of ________________.


Q6. Ozone layer thickness is measured in Q6. Ozone layer thickness is measured in ____________ units.____________ units.

Q7. Formation and destruction of ozone in the Q7. Formation and destruction of ozone in the atmosphere can be explained by ___________ atmosphere can be explained by ___________ reactions.reactions.

Q8. 1 Du = ____________________________.Q8. 1 Du = ____________________________.


Theory QuestionsTheory Questions

Q1. Explain ‘Ozone depletion process with Q1. Explain ‘Ozone depletion process with respect to following pointsrespect to following points

-- Sources/causesSources/causes

-- Chemical reactionsChemical reactions

-- EffectsEffects

-- RemediesRemedies

Q2. Define Dobson unit.Q2. Define Dobson unit.

Q3. Explain Chapman reactions.Q3. Explain Chapman reactions.Prof S S Jahagirdar, NKOCETProf S S Jahagirdar, NKOCET 3838



AIR POLLUTION CONTROL L 11

Technology

reduced survival

explain chapman

uv level decreases

solar uv radiation

solar uvb

define dobson

solar uvb

peak ozone