ESS Standard Topic 6.4

Stratospheric Ozone

Ozone

A molecule composed of 3 oxygen atoms

• Very reactive

The Formation of Ozone

Ozone layer considered to be in steady state equilibrium:

UV radiation passing through the Earth’s upper atmosphere is continuously absorbed by the formation and destruction of ozone.

Where is the Ozone Layer Beneficial?

The stratosphere: Protects the Earth from All UVC radiation and most UVB rays (C being the most dangerous form of Ultraviolet Radiation)

Where is the Ozone Layer Negative?

The troposphere: The ozone reacts with nitrogen creating photo chemical smog (Air pollution)

Ultraviolet Radiations effect on Humans

• Damages human living tissues

• Increases the incidence of cataracts

• Mutation during cell division

• Skin cancer

Ultraviolet Radiations effect on Plants

• Reduces productivity in photosynthetic organisms.

  • Especially phytoplankton – basis of many aquatic food webs.

• Reduced photosynthesis rates

• Altered plant metabolism

• Decreased crop yields

Benefits of Ultraviolet radiation

• In animals it stimulates the production of Vit D.

• Treats psoriasis and vitiligo (skin diseases)

• Steriliser, water purifier

• Forensics, lighting, lasers

Ozone Depleting Substances - in the name

• Chlorofluorocarbons (CFCs) - aerosols or refrigerants

• Hydrochlorofluorocarbons (HCFCs) - blowing agents/foamed plastic

• Halons - fire extinguishers

• Methyl bromide - pesticides

• Nitrogen oxides

Chlorofluorocarbons (CFCs) effect on Ozone

When exposed to UV radiation in the stratosphere they release chlorine or bromine atoms. 

• ODSs react with ozone resulting in ozone destruction. Disturbing the equilibrium

• They can also react with oxygen molecules preventing more ozone from being formed. Through a catalytic chain reaction.

CFCs vs HCFCs

HCFCs have a shorter lifespan, non-flammable and also non toxic but they also destroy the ozone

What happens when the Ozone Layer depletes?

• This leads to increased ozone depletion

• Increased UVB radiation reaches the Earth's surface

• Affects ecosystems and human health

• Causes increased rates of skin cancer and cataracts

• Reduces terrestrial and marine productivity

Annual Ozone Thinning

Holes appear in the Ozone layer every spring as the UV radiation activates the ODSs, releasing chlorine and bromine atoms.

Ozone Holes

Areas of low stratospheric ozone (Worst in the Southern Hemisphere)

United Nations Environment Programme (UNEP)

Formed Key agreements to do with:

• Air pollution

• Contamination of international waterways

• Provide information to countries and the public on disadvantages of pollution

• Brought together 24 countries in 1987 to sign the initial Montreal Protocol on ODSs

Montreal Protocol

An international treaty that regulates the production, trade and use of chlorofluorocarbons (CFCs) and other ODSs. 

It is regarded as the most successful example of international cooperation in management and intervention to resolve a significant environmental issue and prevent from planetary boundary from being crosses.

Strength of the Montreal Protocal

• Raised awareness of CFCs and ozone depletion

• Global Participation: 197 countries now signed- widespread impact

• Legally Binding: Phase out in Europe achieved by 2000 (world 2030?) CFCs🡪 HCFCs (eventually phase out HCFCs by 2040) 

• Flexibility and Adaptation: has been amended several times to adjust to new scientific knowledge 

• Financial and Technical Assistance: LEDC’s granted a longer time to implement the treaty

• Scientific Consensus: based on a solid foundation of scientific research and data 

Limitations of the Montreal Protocol

• Relies on national governments complying and making laws. These need policing (and money)

• There is a black market in ODS

• Old fridges are still in circulation

• ODS remain in the atmosphere for a long time

Reasons for the ODSs Black Market

• ODS substitutes are often costlier than CFCs

• Updating equipment to enable use of alternative chemicals is expensive

• The lifetime of CFC containing equipment is long

• Penalties in many countries are small