Ozone depletion

A vital topic to everyone

Ozone

A gas composed of three atoms of oxygen bluish gas that is harmful to breathe great majority of the ozone is concentrated

on the stratosphere-------which is known as ozone layer.

Out of each 10 million air molecules, about 2 million are normal oxygen, but only 3 are ozone.

The atomic oxygen quickly combines with further oxygen molecules to form ozone:

O2 + hv -> O + O (1) O + O2 -> O3 (2) at ground level, ozone is a health hazard - it is

a major constituent of photochemical smog.

Ozone is also destroyed by the following reaction:

O + O3 -> O2 + O2 (4) The Chapman Reactions

Uses of ozone

Ozone absorbs a band of ultraviolet radiation called UVB that is particularly harmful to living organisms which can cause cancer skin cancer amd damage vegetation

thus it prevents most UVB reaching the ground

When did the hole first appear?

It was first observed by ground-based measurements from Halley Bayon the Antarctic coast, during the years 1980-84

Ozone Hole over Antarctica This model shows the ozone hole during the summer over Antarctica. Within the model,

height represents ozone concentration.

The Science of Ozone depletion

the release of chlorofluorocarbons (CFCs) into the atmosphere could reduce the amount of ozone

Although the UV radiation splits the ozone molecule, ozone can reform through the following reactions resulting in no net loss of ozone:

O3 + hv -> O2 + O (3) O + O2 -> O3 (2) as above

destruction of ozone are:

HCl + ClONO2 -> HNO3 + Cl2 (1) ClONO2 + H2O -> HNO3 + HOCl (2) HCl + HOCl -> H2O + Cl2 (3) N2O5 + HCl -> HNO3 + ClONO (4) N2O5 + H2O -> 2 HNO3 (5)

Remember that these reaction can only take place in the surface

Molecular chlorine is easily photodissociated (split by sunlight):

Cl2 + hv -> Cl + Cl

The production of active chlorine requires sunlight, and sunlight drives the following catalytic cycles thought to be the main cycles involving chlorine and bromine, responsible for destroying the ozone:

(I) ClO + ClO + M -> Cl2O2 + M Cl2O2 + hv -> Cl + ClO2 ClO2 + M -> Cl + O2 + M then: 2 x (Cl + O3) -> 2 x (ClO + O2) net: 2 O3 -> 3 O2

and (II) ClO + BrO -> Br + Cl + O2 Cl + O3 -> ClO + O2 Br + O3 -> BrO + O2

net: 2 O3 -> 3 O2 the above equation is known as 'catalytic

cycles'. A catalytic cycle is one in which a molecule significantly changes or enables a reaction cycle without being altered by the cycle itself.

The production of active chlorine requires sunlight, and sunlight drives the following catalytic cycles thought to be the main cycles involving chlorine and bromine, responsible for destroying the ozone

What is the process of ozone depletion?

What is ODS?

ODS is... Known as ozone depleting substances including: CFCs, HCFCs, halons, methyl bromide,

carbon tetrachloride, and Methyl Chloroform

What is CFCs?

Chloroflurocarbon a compound consisting of chlorine, fluorine,

and carbon very stable in the stratosphere broke down by strong violet light in the

stratosphere and release chlorine atoms that deplete the ozone layer

Effect of Ozone depletion

How much do you know:

Effect

Effects on Human and Animal Health Effects on Terrestrial Ecosystems Effects on Aquatic Ecosystems Effects on Air Quality Effects on Materials

Human and animal

increase in the risk of cataract and skin cancer increases in UV-B radiation associated with

ozone depletion are likely to lead to increases in the incidence and/or severity of a

variety of short-term and long-term health effects

Effects on the immune system(may be beneficial)

Depressed resistance to certain tumors and infectious diseases

potential impairment of vaccination responses increased severity of some autoimmune and

allergic responses decreases in the severity of certain

immunologic diseases/conditions such as psoriasis and nickel allergy. (beneficial)

Effects on Terrestrial Ecosystems Damage to the terrestrial organisms

including plants and microbes. increased UV-B exerts effects more often

through altered patterns of gene activity. affect food quality for humans and grazing

animals

Aquatic life:

solar UV-B and UV-A have adverse effects on the growth, photosynthesis, protein and pigment content, and reproduction of phytoplankton, thus affecting the food web

.

Air quality:

Increased UV-B will increase the chemical activity in the lower atmosphere (the troposphere). Tropospheric ozone levels are sensitive to local concentrations of nitrogen oxides (NOx) and hydrocarbons.

additional UV-B radiation reduces tropospheric ozone in clean environments (low NOx), and increases tropospheric ozone in polluted areas (high NOx).

increase the concentration of hydroxyl radicals (OH) and result in faster removal of pollutants.

Materials

Physical and mechanical properties of polymers are negatively affected by increased UV-B in sunlight. Increased UV-B reduces the useful lifetimes of synthetic polymer products used outdoors and of biopolymer materials such as wood, paper, wool and cotton.

What did the world do:?

1970s

Ban on the use of CFCs as aerosal propellant in several countries

However, production of CFCs and other ozone-depleting substances grew rapidly after the other ozone-depleting substances grew rapidly afterward as new uses were discovered

1980s

World’s nations became increasingly concerned that OSD would harm the ozone layer.

In 1985, the Vienna Convention was signed.

Expected that by 1998 , the production of the CFCs/ODS products would reduce by half

1990s

Decided to completely end production of halons(which is ODS) by the beginnings of 1994

end production of CFCs in 1996

What can we small people do about it?

No, in fact, we play an important role to prevent the situation form

worsening!

At home:

Repair air conditioners this step prevents ozone-depleting

refrigerants from escaping. Make certain the refrigerant is recovered

If you purchase a new air conditioning system or heat pump, purchase one that uses non-ozone-depleting refrigerant. See a fact sheet on this topic.

Remove the refrigerant from refrigerators, air conditioners, and dehumidifiers before disposing of the,

If you suspect or witness unlawful releases of refrigerant or other improper service practices, you can report to the authorities concerned.

If you are car-owners

Repair all leaks in the a/c system About 80 million cars on the road today use

CFC refrigerants in their air-conditioning (AC) systems. If leaky systems were repaired, it would prevent the release of about 30 million pounds of CFCs this year.

Ask about converting your car to a substitute refrigerant if the a/c system needs major repair

bare in mind that :

Everyone have the responsibility to protect our earth.

Will the Ozone Layer Recover? Can We Make More Ozone?

ANS: recovering in 50 years

WHY?

Thanks for watching!!!

Reference materials:

http://www4.nationalacademies.org/beyond/beyonddiscovery.nsf/web/ozone?OpenDocument

www.epa.gov http://www.atm.ch.cam.ac.uk/tour/index.html http://www.nas.nasa.gov/Services/

Education/Resources/TeacherWork/Ozone/Ozone.homepage.html

http://www.epa.gov/docs/ozone/title6/609/cons2.html