Environmental Science - 2.1.3 - Ozone depletion
what is the rowland-molina hypothesis
2 american scientists suggested that the chemical properties of CFCs could lead to ozone depletion in the stratosphere, based on the chemical behaviour
how does CFC persistence cause ozone depletion
they are chemically very stable so remain in the atmosphere for long enough to be carried up to the stratosphere
how does dissociation by UV cause ozone depletion
in stratosphere they are exposed to high levels of UV radiation, causing carbon-chlorine bonds to break and release chlorine free radicals.
how does reaction with chlorine and oxygen
chlorine reacts with monatomic oxygen, preventing the formation of 02 to form 03, preventing the formation of more ozone molecules
how do halogens cause ozone depletion
bromine and iodine can cause similar reactions
what is a CFC
a gas developed in the 1920s for use in air conditioning and refrigeration units as a replacement for ammonia.
what is the effect of ozone depletion on animals and humans
can cause certain skin cancers in humans as cell DNA is mutated, causes cataracts in animals and humans
what is the effect of ozone depletion on the environment
leaf tissue damage causes reduced photosynthesis, and therefore damage to marine organisms such as algae, corals, and phytoplankton
general effects of ozone depletion
more dangerous UV levels let through
what is ozone measured in
Dobson Units (DU)
how is the ozone measured
Dobson units estimate the thickness of the ozone laer as if it exists as pure ozone at sea level
what is 100 dobson unit equal to
1mm
what is the regular thickness of the ozone layer
300 DU (3mm)
what levels does an ozone hole refer to
levels below 220DU
how is ozone depletion recorded at ground level
higher levels of UV being detected is evidence of ozone loss in the stratosphere, collected by the British Antarctica Survey
how is ozone depletion measured by satellites
UV light reflected back out towards space may be measured by satellites higher up than the stratosphere, higher levels indicates that ozone levels have been reduced
how do ozone levels vary temporally
severity of ozone depletion in antarctica is worse between september and december because this is when the southern hemisphere recieves the most sun, and sees the most ozone particles broken up by UV
how do ozone levels vary spatially
ozone levels are generally worse at the poles, due to polar vortexes, which maintain low temperatures that make stratospheric clouds and ice crystals in which CFC reactions may occur
how do ozone levels vary by altitude
most severe at 12-24km where UV light splits ozone and releases monatomic oxygen that reacts with chlorine and prevent future ozone formation
why does low temperatures over antarctica cause ozone depletion
allows for stratospheric clouds and ice crystals to form, gives higher surface area for CFC splitting reactions
what is the montreal protocol (1987)
an agreement that every country in the UN would protect the ozone layer with no legal binding
what were the 4 main aspects of the montreal protocol
banning the production and use of CFCs and ODS
HCFCs phased out by 2030
essential ODS use is still permitted
fund available to help implementation
alternative processes as a result of MP
pump action sprays in place of aerosols
roll on deodorant
alternative materials as a result of MP
HCFCs introduced to replace CFCs, but were less stable, so eventually replaced by HFCs
hydrocarbons replaced CFC aerosol propellants, more flammable and pose a fire risk
what are properties of HFCs
contains no chlorine and does not deplete ozone, more expensive to produce and do not work as well, still GHGs
how are CFCs disposed of
waste CFCs from fridges is drained and those incinerated. the CFCs are broken down into CO2 and acidic gases which are neutralised with crushed lime