ESS UNIT 6.2: Stratospheric Ozone

- what is the ozone layer, issues and dangers for the ozone layer, international action taken and local action

stratospheric ozone

• During the Cambrian Explosion, many complex multicellular organisms evolved in the oceans,

• Marine organisms became mobile and were able to live in shallower areas of the ocean with greater sunlight exposure. 

• Around 420 million years ago, ozone levels were high enough to allow for organisms to survive on land, without any shielding from water

ozone layer

a group of gas called ozone that surrounds the planet and acts as a barrier from the UV rays from the sun

• is found in the stratosphere

• is a trace gas

• is earth’s sunscreen —> absorbs about 97% of uv rays

stratospheric ozone production

• some ultra violet radiation from the sun is absorbed causing ozone molecules to break apart

• under normal conditions the ozone molecule will reform

1. O2 +UV—> O +O

2. O + O2 —> O3

dynamic equlibrium

the destruction and reformation of the ozone atoms

Ozone production

1. nitrogen oxides (NO2) and hydrocarbons in air

2. UV causes NO2 to break into O + NO

3. O reacts with O2 —> O3Remaining NO react to unstable molecules that are products of hydrocarbons oxidizing in the atmosphere recreate NO2

4. vicious cycle of ozone production

How CFCS deplete ozone

1. UV rays causes a chlorine atom to break away from CFC molecule

2. the free chlorine atom hits an ozone molecule

3. the chlorine atom pulls one oxygen atom away

4. free oxygen hits chlorine-oxide molecule

5. creates free chlorine atom

6. free chlorine will continue to deplete ozone in stratoshpereu

Human activities have disturbed the dynamic equilibrium of stratospheric ozone formation

Photokeratitis

sunburn of the cornea due to excessive UV exposure

cataracts

• clouding of eye’s crystalline lens often as a result of execessive UV exposure

photo-again and DNA change of skin

• photoaging of eyelids —> skin thicker —> prominent wrinkles

mutations during cell division,

• DNA readily absorbs UV-B radiation, which commonly changes the shape of the molecule

• Changes often mean that protein-building enzymes cannot “read” the DNA code at that point on the molecule.

• As a result, distorted proteins can be made, or cells can die.

benefits of UV

• In animals stimulates the production of Vit D.

• Treat psoriasis and vitiligo (skin diseases)

• Steriliser, water purifier

• Forensics, lighting, lasers

UV impacts on biological productivity

 The effects of increased ultraviolet radiation on biological productivity include damage to photosynthetic organisms, especially phytoplankton which form the basis of aquatic food webs

• Phytoplankton do not exist in isolation

• Other microbes, the protozoa, bacteria and viruses, can be directly damaged or killed by solar UVB. 

• Due to the interactions between trophic levels of the microbial community, any UVB-induced impact at one level can alter the entire community

UV impacts on photosynthetic organism

• Plants are vulnerable to increased UV-B radiation because many cellular components can absorb UV  directly  

• Increased UV-B radiation has many effects on plant morphology, physiology and development, and its impacts on growth and development

• Reduction in biomass accumulation due to UV-B exposure has been verified 

• Many plants exposed to this radiation exhibit decreased rates of photosynthesis

International Agreements

• The United Nations (UN) was instrumental in establishing binding legislation to encourage countries to reduce damage to the ozone layer. 

• Vienna Convention in 1985

• Montreal Protocol in 1987.

  • In 2009, it became the first UN treaty to be ratified by all 197 nations.

Montreal Protocol 1987

 is an international agreement for the reduction of use of ozone-depleting substances signed under the direction of UNEP. National governments complying with the agreement made national laws and regulations to decrease the consumption and production of halogenated organic gases such as chlorofluorocarbons (CFCs)

Montreal Protocol Progress

Implementation of the Montreal Protocol has resulted most of the main ODS to be banned with some exceptions for medical and research use. 

• CFCs production has stopped and are resulting in atmospheric levels stabilizing or declining.

• Production of halons has stopped, but atmospheric levels continue to rise, possibly due to emissions from old fire extinguishers.

HFC Kigali Amendment to the Montreal Protocol – 2019

• environmental issues need to be addressed at an intergovernmental level;

• changes in behavior 

• MEDCs agreed to provide financial assistance LEDCs;

• technological development has found alternatives to HFCs;

Challenges of ban

• Long life span of ODS

• ODS present in discarded equipment

• Lack of alternatives

• Replacement chemicals also ODS

• Lack of policing and enforcement

• Illegal markets

An illegal market for ozone-depleting substances persists and requires consistent monitoring

Pollution Management

may be achieved by reducing the manufacture and release of ozone-depleting substances. Methods for this reduction include:

Tier 1 strategy for reduction

• Campaign to educate public and pressure,  industry to find and use suitable replacement

tier 2 strategy for reduction

Policing and enforcement to ensure compliance, recover and recycle CFCs from refrigerators and AC units

Tier 3 strategy for reduction

Remove and destruction of ozone-depleting compounds