Ozone Depletion

By : Brian Antony D'Souza

Earth’s Atmosphere

What is ozone ???

The ozone• The ozone layer is a layer in Earth's

atmosphere which contains relatively high concentrations of ozone (O3).

• Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the sun.

• O3 is mainly found in the stratosphere.

• O3 both heats the stratosphere by absorbing UV and is a greenhouse gas (absorbing and emitting in the Infrared).

What chemicals cause ozone loss ???

Ozone Depleting Substances

o Chlorofluorocarbons (CFC’s)

Freon from old air conditioners and refrigerators and from industry is one of the big sources.Chlorofluorocarbons (cfcs) were invented by Thomas Midgley in the 1920s. They were used in air conditioning/cooling units, as aerosol spray propellants prior to the 1980s, and in the cleaning processes of delicate electronic equipment. They also occur as by-products of some chemical processes. No significant natural sources have ever been identified for these compounds — their presence in the atmosphere is due almost entirely to human manufacture.

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CHEMICAL MECHANISM

Chlorofluorocarbon's: - CFC’s contain : Cl, Fl, C - Non-toxic, non-flammable i.e. inert in the troposphere.

- In the stratosphere are photolysed, releasing reactive chlorine atoms.

- The chlorine atoms act as a catalyst, and each can break down tens of thousands of ozone molecules to oxygen.

STRATOSPHERIC OZONE AND ULTRAVIOLET RADIATION (UVR)

• Ultra-violet radiation (UVR) high energy electromagnetic wave emitted from the sun. It is made up of wavelengths ranging from 100nm to 400nm.

• UV radiation includes UV-A, the least dangerous form of UV radiation, with a wavelength range between 315nm to 400nm, UV-B with a wavelength range between 280nm to 315nm, and UV-C which is the most dangerous between 100nm to 280nm. UV-C is unable to reach Earth’s surface due to stratospheric ozone’s ability to absorb it.

Ozone destruction impact

TOO MUCH ULTRA-VIOLET-B ON HUMAN BEINGS• Skin cancer:90% of the

skin carcinomas are attributed

• Eye damage such as cataracts : Increases the risk of cataracts

• Induces type of protein that provokes cleaving (splitting) in the lens

• Leading cause of blindness

• The prevalence of cataract after age 30 is doubling each decade

• Immune system damage : Enhanced susceptibility to infection

• DNA absorbs UV-B radiation • Changes shape in DNA

• Changes in the DNA molecule mean that enzymes cannot “read” the DNA code

• Results in mutated cells or the cells die

• Cells have developed the ability to repair DNA• A special enzyme arrives at the damage site

• removes the damaged section of DNA

• replaces it with the proper components

• This makes DNA somewhat resilient to damage by UV-B

Dna and uv

The influence of the UV-b radiation on plant process. In experimental series the following observationswere determined: number of leaves, tillering of plants recordedafter three weeks and before harvest plant height,biomass of plants, specific leaf weightsleaf: shoot dry ratio, shoot dry matterof chlorophyll. Leaf area was measured using a LICOR LI-30004 portable leaf area meter and the content oftotal chlorophyll was measured with a Minolta SPAD-502meter5.

Phytoplankton• UV-B penetrates water columns to depths of 30m

• Increased UV-B exposure

• Reduces productivity by interfering with processes of photosynthesis

• Damages DNA

• Inhibits mobility

• Studies (1993) conducted in the Weddle Sea

• Evaluated effects of photosynthesis to UV exposure in the presence of vertical mixing, found:

• photosynthesis by phytoplankton was strongly inhibited near the surface of the water

The ozone hole discovery

The DISCOVERY

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

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

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

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

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

What is being done to counter the effects of ozone depletion ???

Signs of recovery ???There have been some signs of

recovery

• Since the Montreal Protocol came into effect, the atmospheric concentrations of the most important chlorofluorocarbons and related chlorinated hydrocarbons have either levelled off or decreased.

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

• Satellite images show some slowing down of ozone loss

• Ozone is the critical gas for screening solar UV radiation. Quality, long-term observations are critical for assessing change!

• Ozone loss resulted from human produced ozone destroying substances (ODS: CFCs ). These chemicals have extremely long lifetimes.

• ODSs have been regulated under international agreements and are slowly decreasing.

• Ozone levels are not getting worse, but we can’t say that things are getting better (yet).

• The ozone hole will recover by about 2068.

Summary

Thank you