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Chlorofluorocarbons andthe Ozone Layer

The Stratosphere and the OzoneLayer

The Ozone Layer

• It refers to the ozone withinstratosphere, where over 90% of the earth's ozone resides.

• Ozone is an irritating, corrosive,colorless gas with a smellsomething like burning electricalwiring.

• Ozone is easily produced by anyhigh-voltage electrical arc (sparkplugs, Van de Graaff generators,

Tesla coils, arc welders).

• Each molecule of ozone has threeoxygen atoms and is producedwhen oxygen molecules (O2) arebroken up by energetic electrons orhigh energy radiation.

O + O 2 → O3

• It absorbs 97-99% of the sun's highfrequency ultraviolet light , lightwhich is potentially damaging to lifeon earth.

• But worldwide, the ozone layer isthinning as the total amount of ozone decreases.

• In 1985, the British Antarctic Surveyteam discovers Antarctic Ozone

Hole (7.3M square miles), markingthe first evidence of stratosphericOzone Depletion.

• Depletions in the ozone can causesunburn, skin cancer and eyedisease.

Causes of Ozone Layer Depletion

• The following chemicals affect the

Ozone layer:Chlorofluorocarbons or CFCs – main factorof Ozone depletion

Halons - are bromine-containingfluorocarbons that are used in fireextinguishers, although they maycontribute to depletion of the ozone layer

Bromomethane or Methyl Bromide (CH 3Br)– a pesticide, and an agricultural fumigantbut phase-out by many countries.

* In 1975, scientists discover thatbromine, used in fire-retarding halons andagricultural fumigants, is a potent ozone-depleting substance.

Chlorofluorocarbons

• These are small gaseous moleculescontaining carbon, chlorine andfluorine.

• It was first created in 1928 as non-toxic, non-flammable refrigerants,and were first produced

commercially in the 1930's byDuPont.

• Examples are CFCl 3 (Freon 11) andCF2 Cl2 (Freon 12)

• These are widely used as:

Dry-cleaning solvents

Refrigerants forfreezers, airconditioners, andrefrigerators

Propellant in aerosolcans

Foaming agents forplastics

• In 1973, scientists detect CFCs inthe atmosphere.

• In 1974, Mario Molina and F.Sherwood Rowland published alaboratory study demonstrating theability of CFC's to catalyticallybreakdown Ozone in the presenceof high frequency UV light.

• In 1970, Paul Crutzen, showed thatnaturally occurring nitrogen oxidescatalytically destroy ozone.

• In 1995 the Nobel Prize forChemistry was awarded to the threeof them for their studies of ozonedepletion in the stratosphere.

So why are CFCs harmful?

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Because UV lightcauses CFCs todissociate and producechlorine atoms,chlorine free radicals.

Chain Initiation: CF 2Cl2 → CF2Cl + Cl

These chlorine atomsreact to form chlorinemonoxide andmolecular oxygen, so amolecule of ozone isdestroyed.

Chain Propagation: Cl + O 3 → ClO + O 2

But again chlorine

monoxide reacts withnaturally occurringoxygen atoms toregenerate the originalchlorine radical andmolecular oxygen.

ClO + O → Cl + O 2

* A free radical chain reaction is initiatedby each CFC that is dissociated, and each

chain reaction results in the destruction of thousands of molecules of Ozone.

CFCs VS HCFCs/HFCs and otherAlternatives

• Why use HCFCs than CFCs?

Because HCFCs are less-threatening,energy-efficient, low-in-toxicity, costeffective and can be used safely.

Hydrogens on HCFCs make them moresusceptible to oxidation and destruction inthe lower atmosphere.

HFCs have C – H bonds rather than C-Clbonds of CFCs

• What are other Alternatives asideHCFCs /HFCs ?

We can also use gaseous hydrocarbons

such as butane and propane

Action of the Society onCFC and its Effects

• In 1976, the United NationsEnvironmental Programme (UNEP)calls for an international conference

to discuss an international responseto the ozone issue.

• In 1978, U.S. bans non-essentialuses of CFCs as propellant in someaerosols. Canada, Norway andSweden follow with the similar ban.

• In 1981, UNEP develops a globalconvention to protect the ozonelayer.

The Montreal Protocol

• In September 16, 1987, 24countries sign the Montreal Protocolon Substances that Deplete theOzone Layer.

• An international treaty designed toprotect the ozone layer by phasingout the production of a number of substances believed to beresponsible for ozone depletion

• It undergone many revisionsthrough the years, example is in inCopenhagen in November of 1992,laid down the most stringent CFC

phase-out schedule for CFC's for theworld to date; and was signed byover 100 nations representing 95%of the world's current CFCconsumption.

• This protocol laid out a schedule forthe phase-out of CFC's and relatedhalocarbons by the year 2030.

• In 1988, Sweden was the first

country to legislate the completephase-out of CFC's, with ascheduled phase-out of CFC's in allnew goods by 1994.

• In 1990, an amended federal CleanAir Act was signed into law. Thislegislation included a section (TitleIV) entitled Stratospheric OzoneProtection

•

In 1992, U.S. announces anaccelerated CFC phase-out date of December 31, 1995.

• In 1993, Du Pont announces that itwill stop its production of CFCs bythe end of 1994.

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• In 1994, U.S. eliminates productionand import of halons.

• In 1996, U.S. eliminates productionand import of CFCs , carbontetrachloride, trichloroethane, andhydrobromofluorocarbons.

• In 2000, Japan MeteorologicalAgency reports the hole in thestratospheric ozone layer overAntarctica is as its largest to date –more than twice the size of Antarctica.

• In 2002, all developing countriesfreeze the production of MethylBromide.

• In 2004, all developed countriesreduce consumption of hydrochlorofluorocarbons (HCFCs)by 35% from baseline level.

• In 2006, the ozone hole is reportedto be the biggest ever, exceedingthat of 2000.

• In the year 2060 – 2075, earliest

time frame of projected for theozone layer to recover.

GENERAL ANESTHETICS

• These are groups of relatively

nontoxic, nonflammable, easilyvaporized organic liquid used forthis purpose.

• Its effects is called GeneralAnesthesia which is an induction of a balanced state of unconsciousness, accompanied bythe absence of pain sensation andthe paralysis of skeletal muscleover the entire body.

• These are used in personsundergoing a major surgery to keptthem unconscious, withoutperception of sensations, for acontrolled period of time withoutdanger of death or toxic sideeffects.

• Five distinct states duringsurgery:

• analgesia, or painrelief

• amnesia, or loss of

memory of theprocedure

• loss of consciousness

• motionlessness

• weakening of autonomic responses

• Before giving GeneralAnesthetics:

The medical personnel should know themedical history of the patients likeallergies.* Malignant Hyperthermia - potentiallyfatal allergic response to anesthesia

Consider many factors, including apatient's age, weight, allergies tomedications, medical history, and generalhealth when deciding which anesthetic or

combination of anesthetics to use.

Why General Anesthetics can causeunconsciousness or Anesthesia?

• Membranes of our bodies, includingthose of the nerve cells in ourbrains, are largely hydrocarbon instructure, then anesthetics can passinto our cells rapidly and exit just asquickly.

• There are, however, severalhypotheses that have beenadvanced to explain why generalanesthesia occurs:

1. Meyer-Overton theory - suggests thatanesthesia occurs when a sufficientnumber of molecules of an inhalationanesthetic dissolve in the lipid cellmembrane.

2. The second theory maintains thatprotein receptors in the central nervoussystem are involved, in that inhalationanesthetics inhibit the enzyme activity of proteins.

3. A third hypothesis, proposed by LinusPauling in 1961, suggests that anesthetic

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molecules interact with water moleculesto form clathrates (hydratedmicrocrystals), which in turn inhibitreceptor function.

Types of anesthetic agents

There are two major types of anestheticsused for general anesthesia,

• Inhalation anesthetics

- are sometimes called volatileanesthetics, are compounds thatenter the body through the lungsand are carried by the blood tobody tissues.

- Less often used alone in recentclinical practice; they are usuallyused together with intravenousanesthetics.

• Intravenous anesthetics

- giving medications or fluids(solutions) through a needle or tubeinserted into a vein

INHALATION ANESTHETICS

• Halothane

- Causes unconsciousness butprovides little pain relief; oftenadministered with analgesics

- It may be toxic to the liver inadults.

- has a pleasant smell and istherefore often the anesthetic of choice when mask induction isused with children.

- This halogenated hydrocarbonwas first synthesised by C. W. Suckling of Imperial Chemical Industries (ICI) in 1951 and wasfirst used clinically by M.

Johnstone in Manchester in1956.

• Enflurane

- less potent, butproduces a rapid onsetof anesthesia andpossibly a fasterrecovery

- not used in patientswith kidney failure

- Developed by Ross Terrell in 1963, it wasfirst used clinically in1966.

• Isoflurane

- not toxic to the liverbut can induce

irregular heart rhythms• Sevoflurane

- works quickly and canbe administeredthrough a mask sinceit does not irritate theairway

- On the other hand, oneof the breakdownproducts of sevoflurane can causerenal damage

• Methoxyflurane

- was commonly used asan inhalationanesthatic in the1960s and early 1970s

- As largely beenabandoned because of detrimental effects onthe kidneys

INTRAVENOUS ANESTHETICS

• Ketamine

- produces a differentset of reactions from

other intravenousanesthetics

- have sensory illusionsand vivid dreamsduring post-operativerecovery, ketamine isnot often given toadult patients

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- useful in anesthetizingchildren, patients inshock, and traumacasualties in war zoneswhere anesthesiaequipment may bedifficult to obtain

• Thiopental (a barbiturate)

• Methohexital

• Etomidate

• Propofol