Organohalogen compounds in the atmosphere Flashcards
What are organohalogen compounds?
Molecules that contain at least one halogen atom joined to a carbon chain
They have practical uses and are used in many pesticides.
Are organohalogen compounds commonly found in nature?
No, they are rarely found in nature and are not broken down naturally in the environment
This has led to concerns about their impact.
Where is the ozone layer located?
At the outer edge of the stratosphere, 10 to 40 km above the Earth’s surface
It absorbs most biologically damaging UV-B radiation.
What is the primary function of the ozone layer?
To absorb most of the biologically damaging ultraviolet radiation (UV-B) from the Sun
This protects living organisms from increased genetic damage.
What is UV-B radiation linked to?
Sunburn and harmful effects on living organisms
Increased exposure can lead to greater risk of skin cancer in humans.
How is ozone formed and broken down in the stratosphere?
By the action of ultraviolet (UV) radiation
High energy UV breaks oxygen molecules into radicals, leading to a steady state of ozone formation and breakdown.
What human activity has upset the equilibrium of ozone formation?
Production and use of chlorofluorocarbons (CFCs)
CFCs disrupt the natural balance of ozone formation and breakdown.
What are CFCs commonly used for?
As refrigerants, in air-conditioning units, and as aerosol propellants
CFCs were widely used due to their stability.
What happens to CFCs in the stratosphere?
They break down, forming chlorine radicals
These radicals catalyse the breakdown of the ozone layer.
What is photodissociation?
The process where UV radiation initiates the breakdown of CFCs
It involves breaking carbon-halogen bonds to form radicals.
What is the result of the reaction involving chlorine radicals and ozone?
Chlorine radicals react with ozone, breaking it down into oxygen
This occurs in a chain reaction, allowing one CFC molecule to promote the breakdown of many ozone molecules.
Are CFCs responsible for all ozone-depleting reactions?
No
Other radicals, such as nitrogen oxide radicals, also catalyse the breakdown of ozone.
How do nitrogen oxide radicals break down ozone?
Through a mechanism similar to that of chlorine radicals
They are formed during lightning strikes and aircraft travel in the stratosphere.
