Since the 1970s reduction in atmospheric ozone has been observed in 2 ways:
- general global reduction of about 4% per decade over whole planet
- so-called 'ozone-holes' in polar regions where there is an annual drop in stratospheric ozone concentrations. Consentrations over Antartica have dropped by up to two-thirds while over Arctic there is one third drop
Why is there concern about ozone depletion?
- If UVB not absorbed in atmosphere then will reach Earth's surface and absorbed by living cells
- energy of UVB is absorbed and some is converted into chemical energy as it breaks up biological molecules causing damage to the DNA in exposed cells, skin cancer, cataracts and damage to plant tissue and marine plankton
UV light absoption
ultraviolet light categorised by its wavelength:
UV A - 320-400nm - Not absorbed by ozone
UV B - 280-320nm - Almost fully absorbed by ozone
UV C - <280nm - Completely absorbed by ozone and normal oxygen
UV light considered in studying ozone depletion is UVB.
The effects of UVB light on the gases in the atmosphere
UVB is involved in a number of chemical reactions. Absorbed in providing energy for reactions so very little raeches the Earth's surface.
UVB absorbed by both diatomic and triatomic oxygen in photolytic reactions where molecules are spilt. Products of these reactions are involved in futher reactions.
How does chlorine get to the stratosphere?
Chlorine is very reactive so if…