Ozone Depletion
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Reactions between UV radiation and oxygen: UVC
UVC + O2 —> O + O
Reactions between UV radiation and oxygen: UVB
UVB + O3 —> O2 + O
Reactions between monatomic and diatomic oxygen
O + O2 —> O3 + heat
Dynamic equilibrium
a combination of active processes that cancel out each other’s effects so that there is no overall charge
Effects of UVB on living organisms
skin cancer, causes cataracts, damages leaf tissue
What pollutant gas contains chlorine?
chlorofluorocarbons
Properties of CFCs
non - toxic inflammable
History of CFCs
Anthropogenic Created due to methyl chloride accidents 1974 - discovered that CFCs were responsible for ozone depletion 1987 - 27 nations signed the Montreal Protocol
Sources of CFCs
refrigerators air con propellants paints fire extinguishers
What was the Rowland-Molina principle?
1974 paper CFCs are broken down by UV in stratosphere to form halogen free radicals, which catalytically react with ozone
Depletions - Cl
Cl + O3 —> ClO + O2 slows O3 formation
Depletions - ClO
ClO + O —> Cl + O2 Cl is released, breaks down more ozone
Why is ozone depletion greatest at polar regions?
cold temp polar vortex winds above poles prevent air from mixing and spreading stratospheric clouds - contain ice crystals which allow for more reactions that release Cl
What other gases cause ozone depletion?
bromine, iodine, fluorine HCFCs
What is ozone measured in?
Dobson Unites (DU)
100 DU =
1mm of O3
What is the regular level of ozone?
300 DU
What level is considered as a hole in the ozone layer?
below 220 DU
Atmospheric monitoring - helium balloons/UAVs
samples are collected and analysed from the air
Atmospheric monitoring - ground based surveys
measures UV reaching Earth’s surface more UV = less O3
Atmospheric monitoring - satellites
measure reflected UV and re-emitted IR from Earth’s surface
What does the Montreal Protocol regulate?
the consumption of ozone depleting substances (ODS)
Who was the Montreal Protocol signed by?
all 198 UN member states
What was agreed in the Montreal Protocol?
all nations had equal responsibilities (e.g. controlling ODS trade) timeline of change was longer for less economically developed countries (LEDCs)