Question 4 Explain how information on changes in atmospheric ozone concentrations is obtained Anita and Lily

Ozone (O 3 ) Pale blue and highly reactive gas with a pungent odour Allotrope of oxygen Troposphere = 10% Stratosphere = 90% In the stratosphere it acts as a primary UV radiation shield

Vast majority of the atmospheric ozone occurs in the stratosphere

Photochemical Smog N 2(g) + O 2(g)  2NO (g) due to the high temperature in engines 2NO (g) + O 2(g)  2NO 2(g) released from car exhaust and oxidised in air NO 2(g) + UVlight  NO  (g) + O  (g) forming oxygen radical O  (g) + O 2(g)  O 3(g)

Causes for ‘ozone hole’ Thinning of the ozone layer CFCs - They remain in the troposphere for decades and eventually find their way to the stratosphere - CCl 3 F (g) + UVlight  Cl● (g) + CCl 2 F● (g) CCl 2 F● (g) + UVlight  Cl● (g) + CClF● (g) - Cl● (g) + O 3(g)  ClO● (g) + O 2(g) - ClO● (g) + O● (g)  O 2(g) + Cl● (g)

Halons - Produces bromine radicals which are even more detrimental than Cl radicals - Br● (g) + O 3(g)  BrO● + O 2(g) Carbon Tetrachloride - Solvents Cl 2 + u.v light  2Cl - Can destroy ozone in the same way as Cl atoms from CFC’s

Effects of the ‘ozone hole’ Cellular damage e.g. sunburn on mammalian skin Changes in plant growth Plankton and the ecosystem Terrestrial plants, in particular agricultural crops Skin cancer Damage to the immune system (diseases) Respiratory problems

Ways to obtain changes in atmospheric ozone concentrations UV Spectrophotometers UV light from satellite High-flying aircraft Balloons Lasers fired from ground