Ozone Layer and Extinction of Species

Contents Ozone layer depletion Extinction of species and loss of

biodiversity

Ozone Layer Depletion

Source of ozone

Consisted of 3 oxygen atoms, unlike ordinary oxygen molecule (which has 2 atoms).

It has a bluish colour.

Dual role of Ozone At near ground level, ozone is an air polluta

nt. Even at a low concentration (ppm), it is irritating to respiratory system.

It is strongly oxidizing, and is now commonly used in sterilization of water.

Its presence in the stratosphere is vital to life on Earth as it can absorb harmful ultra-violet radiation (known as UVB, wavelength 270-315nm) from sunlight.

Structure of Atmosphere

Source: NASA

Formation of Ozone in stratosphere

O2 + (radiation < 240nm) → 2 O O2 + O + M → O3 + M

Molecule M carries the energy of the reaction but remain unchanged.

Destruction of Ozone (I) Ozone can be destroyed by a number of free radical c

atalysts, the most important of which are the hydroxyl radical (OH·), the nitric oxide radical (NO·) and atomic chlorine (Cl·) and bromine (Br·).

Human activity has dramatically increased the chlorine and bromine. These elements are found in certain stable organic compounds, especially chlorofluorocarbons (CFCs), which may find their way to the stratosphere without being destroyed in the troposphere due to low reactivity. Once in the stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action of ultraviolet light, and can destroy ozone molecules through a variety of catalytic cycles.

Destruction of Ozone (II)

Cl + O3 → ClO + O2

ClO + O → Cl + O2

In sum O3 + O → O2 + O2

=>Increase rate of recombination of oxygen, leading to an overall decrease in the amount of ozone.

Ozone hole in September 2006

“Largest hole in the record.”~Size of North America

Source: NASA

Concentration Ozone in Antarctic region

Consequences of Ozone depletion Since the ozone layer absorbs UVB

ultraviolet light from the Sun, ozone layer depletion is expected to increase surface UVB levels.

Possible linked to higher incidence of skin cancer.

Lead to decrease of crop yield.

Montreal Protocol

The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion. The treaty entered into force on January 1, 1989.

Due to its widespread adoption and implementation it has been hailed as an example of exceptional international cooperation

"Perhaps the single most successful international agreement to date...".

Ozone Depleting Substances Chlorofluorocarbons (CFCs) were used in

air conditioning/cooling units, as aerosol spray propellants prior to the 1980s, and in the cleaning processes of delicate electronic equipment.

It is calculated that a CFC molecule takes an average of 15 years to go from the ground level up to the upper atmosphere, and it can stay there for about a century, destroying up to 100,000 ozone molecules during that time.

Current situation CFCs have been replaced to some extent by t

he less damaging hydro-chloro-fluoro-carbons (HCFCs), although concerns remain regarding HCFCs also. In some applications, hydro-fluoro-carbons (HFCs) have been used to replace CFCs.

HFCs, which contain no chlorine or bromine, do not contribute at all to ozone depletion although they are potent greenhouse gases.

Recovery of Ozone Layer Since the adoption and strengthening of the

Montreal Protocol has led to reductions in the emissions of CFCs, atmospheric concentrations of the most significant compounds have been declining. These substances are being gradually removed from the atmosphere.

By 2015, the Antarctic ozone hole would have reduced by only 1 million km² out of 25

Complete recovery of the Antarctic ozone layer will not occur until the year 2050 or later.

A detectable recovery will not occur until around 2024, with ozone levels recovering to 1980 levels by around 2068.

Extinction and Loss of Biodiversity

“Earth’s Sixth Mass Extinction” Since 1500 AD, 784 extinctions have been

documented by the International Union for Conservation of Nature and Natural Resources.

However, since most extinctions are likely to go undocumented, scientists estimate that during the last century, between 20,000 and two million species have become extinct, but the precise total cannot be determined more accurately within the limits of present knowledge.

The World Conservation Union’s IUCN Red List contains 15,589 species threatened with extinction in 2004.

According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, nearly 70 percent of biologists believe that we are currently in the early stages of a human-caused mass extinction

The same proportion of respondents agreed with the prediction that up to 20 percent of all living species could become extinct within 30 years (by 2028).

Cause of extinction of species Deforestation Habitat destruction, degradation or

fragmentation Over-exploitation / hunting Human population growth Pollution Introduction of exotic species Climate change

Some examples of extinct species

Dodo on a flightless bird living onA small island in Indian Ocean. TheyAre hunted to extinction in late 17th Century by sailors and dogs broughtBy them as food.

Baiji, Chinese River DolphinDeclared functionaly extinct in 2006

Bali Tiger gone extinct in 1937

Link

Extinction of Species and Biodiversity Extinction of species cause a

irreversible loss of biodiversity.

Importance of biodiversity Possible new sources of food and

drink in unknown species Possible new medicine Possible new industrial materials Ecosystem provides important vital

resources such as oxygen, fresh water and food.

Leisure, cultural and aesthetic value

Discussion Question What can we do in response of the

mass extinction of species?