Ozone Layer Depletion

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Why the hole in the atmospheric ozone layer above us? What has been done about this? Why should I worry ourselves about the Ozone Layer Depletion?

Good life at the beach threatened?

Mr. OZONE: Will I be able to continue enjoying this life without problems?

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 the United States, over Antarctica.

British Atlantic Survey Research station, Holly Bay, Antarctic Team who discovered the hole 1985. From left: Joe Farman, Brian Gardiner, and Jonathan

Total Ozone Mapping Spectrometer (TOMS) 

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Used by NASA to measure ozone concentrations TOMS – a satellite-borne instrument

TOMS launched in 1996 – makes 35 measurements every 8 seconds Levels of ozone are measured in Dobson units (DU), where 100 DU is equivalent to a 1 millimeter thick layer of pure ozone

Artist's view of the QuikTOMS spacecraft (image credit: NASA)

Earth’s Atmosphere

The ozone layer •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 is being destroyed by CFCs and other substances. • Ozone depletion progressing globally except in the tropical zone. www.epcc.pref.osaka.jp/apec/

What is Ozone? Ozone Layer? 

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Ozone (O3) is a highly-reactive from of oxygen.

Unlike oxygen (O2), ozone has a strong scent and is blue in color. Ozone exists within both the tropospheric and stratospheric zones of the Earth’s atmosphere In the troposphere, ground level ozone is a major air pollutant and primary constituent of photochemical smog

In the stratosphere, the ozone layer is an essential protector of life on earth as it absorbs harmful UV radiation before it reaches the earth.

Hole Formation Based on Two different mechanisms: 

Meteorological mechanism • Movement of air from one place to another in the upper stratosphere • Cold temperature in the upper atmosphere causes nitric acid to freeze into crystals forming wispy pink clouds • Forms a vortex of tightly twisted winds thus forming a hole in the upper atmosphere

Chemical Mechanism

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Different chemicals are responsible for the destruction of the ozone layer Topping the list : • chlorofluorocarbons (CFC’s) • man-made, non-toxic and inert in the troposphere • In the stratosphere are photolysed, releasing reactive chlorine atoms that catalytically destroy ozone

A combination of low temperatures and elevated chlorine and bromine concentrations are responsible for the destruction of ozone in the upper stratosphere thus forming a “hole”. (Kerr, 1987)

www.met.sjsu.edu/~cordero/ education/ed

The Ozone Layer

• 16 – 35 km (above bkgd level) • Stratosphere contains about 90% of all atmospheric ozone • Total column ozone: ~300 DU (1 DU = 0.3 cm thick layer at 1 atm)

– What is the maximum concentration of ozone in the ozone layer? • Maximum of absolute conc about 23 km (up to 1013 molecules/mL) • Maximum of relative conc about 35 km (up to 10 ppm)

CFC’s and ozone depletion 

Chlorofluorocarbons are created and used in refrigerators and air conditioners. These chlorofluorocarbons are not harmful to humans and have been a benefit to us. Once released into the atmosphere, chlorofluorocarbons are bombarded and destroyed by ultraviolet rays. In the process chlorine is released to destroy the ozone molecules

Destruction of ozone by chlorine

Molecular oxygen is broken down in the stratosphere by solar radiation to yield atomic oxygen, which then combines with molecular oxygen to produce ozone. The ozone is then destroyed by chlorine atoms.

Ozone destruction by UV rays 

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UV radiation from the sun releases the radicals Cl and ClO. Ozone is a highly unstable molecule so it readily donates its extra oxygen molecule to free radical species such as hydrogen, bromine, and chlorine. These compound species act as catalysts in the breakdown of ozone molecules.

The ozone depletion process

Responsibility for ozone damage each year

Global CFC production

Ozone hole in September 2006

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

Source: NASA

Ozone hole in Southern hemisphere October 1979 & 1998

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Monthly means of total ozone in the Southern Hemisphere observed with TOMS (Total Ozone Mapping Spectrometer) Images for October of 1979 (left) and 1998 (right).

Ozone concentration at the center of ozone hole

Effects of UV rays on Aquatic Ecosystems Ozone depletion causes increases in UV rays’s effects on aquatic ecosystems by: 1. decreasing the abundance of phytoplankton – affects the food stock for fishes and the absorption of CO2 2. decreasing the diversity of aquatic organisms – reduces food stock and also destroys several fish and amphibians.

Effects of UV rays on Terrestrial Ecosystems 

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Damage to plant cell DNA molecules - makes plants more susceptible to pathogens and pests Reductions in photosynthetic capacity in the plant - results in slower growth and smaller leaves Causes mutations in mammalian cells and destroys membranes

Harmful effects of UV rays on people  

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Skin cancer Premature aging (photoaging) of the skin (different from normal chronological aging) Cataracts and eye disorders (corneal sunburn and blindness) Immune system damage

Correlation between Ozone depletion and skin diseases