Stratospheric Ozone Depletion

By: Natalie Bahou & Yasmeen Al-Qadi

Stratospheric Ozone Depletion

By: Natalie Bahou & Yasmeen Al-Qadi

Definition of ozone depletion

Ozone layer depletion is the reduction of the amount of ozone in the stratosphere, caused by substances formed from breakdown of ozone depleting substances (manufactured chemicals).

Overall structure and composition of the

atmosphereLayers within the atmosphere (from the ground up) and their characteristics

Troposphere -

0-12km thick;

75% of all gases in atmosphere;

all weather happens here;

temperature falls with altitude

Stratosphere -

12-50 km thick

temperature increases with altitude (gets warmer!)

horizontal winds (jet stream)

contains ozone layer

Mesosphere - 50-80km thicktemperature falls with altitude meteor showers happen here

Thermosphere - aurora borealis and aurora australis ionosphere here (reflects radio waves for communications) can be very very hot (2000 C+) !

Exosphere -outermost layer of earth’s atmosphere550km+ above earth’s surfacesatellites orbit here

 

The role of ozone in the absorption of ultraviolet

radiation allows UVa and UVb through, but blocks UVc waves

UVa - causes wrinkles

UVb - causes skin cancer

UVc - worst one because of damage to organisms/tissues

O2 + O + UV → O3 the energy provided by incoming UV light changes O2 → O3

The interaction between ozone and halogenated

organic gases HOG’s are usually stable but break down into halogen atoms (F, Cl, Br, I, At) which are highly reactive (CFC = chlorofluorocarbon; Cl and F are halogens; organic = contains carbon, therefore CFC = halogenated organic compound) How ozone is depleted by CFC’s:

UV radiation breaks off a chlorine atom from a CFC molecule.

The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the ozone.

The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO).

The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule (O2).

The chlorine atom is now free to attack and destroy another ozone molecule (O3). One chlorine atom can repeat this destructive cycle thousands of times.

sources of HOG’s - fire extinguishers, refrigerators, AC units

The effects of ultraviolet radiation on living

tissues and biological productivity

reacts with melanin in skin to cause sunburn & skin canceroverexposure degrades immune system (but how?) required for production of vitamin D (a good thing)interferes with photosynthesis in producers (esp. phytoplankton)zooplankton then gain less energy from phytoplankton, and food chain suffers (i.e. productivity decreases)

Three methods of reducing the

manufacture and release of ozone‑depleting

substances Ozone-depleting substances: CFC’s, halogenated organic gases

• Reduce-Regulate-Restore modelReduce:

replace gas-blown plastics because…

replace CFC’s with CO2, propane, or air

replace aerosol propellants

replace methylbromide pesticides with something other than GHG’s

don’t use aerosol hair products or deodorant - use alternatives (gel, mousse, roll-ons etc)

• Regulate:recover and recycle CFC’s from refrigerators and AC units

HCFC’s are better because they don’t persist as long in the atmosphere; however, they are still harmful to the ozone layer (just less so than CFC’s)

legislate to have refrigerators returned to the manufacturer in order to recover materials used in building them

capture CFC’s from scrap cars AC units

• Restore:remove chlorine from the stratosphere or add ozone (not exactly feasible!)

ozone layer is slowly replenishing itself as long as we continue the ban (see below)

 

The role of national and international organizations in

reducing the emissions of ozone‑depleting substances  

UNEP (United Nations Environment Programme) forges agreements on:

ITIHC (International Trade in Harmful Chemicals)

air pollution

contamination of international waterways

provide information to countries and public on disadvantages of pollution

1987 Montreal Protocol international agreement on the emission of ozone-depleting substancesfroze production and consumption of CFC’s with goal of zero production by year 2000LEDC’s granted a longer time to implement the treatyChina and India have not met their quotas under the MP because of their rapid economic growth and high demand for refrigeration & AC’sgood example of a successful international cooperative effort to alter human impact on the environment