Madeleine Prell
HSC CHEMISTRY 2015​.
OZONE? The Good & Bad
Ozone in the Troposphere
10% of ozone (O3) is found in the troposphere where it is a pollutant
The natural composition of the troposphere is: O3 – 0.02ppm, N2 – 8.8x10^6ppm, O2 – 2x10^6ppm
Photochemical Smog: a type of air pollution that is produced when sunlight acts upon exhaust gasses to form ozone and other harmful substances.
Formation: Ground level ozone forms in sunny conditions, where NO2 concentrations are high, and there is little wind to disperse the pollutants.
Sunlight causes the NO2 to lose an O∙ atom, which combines with O2 forming O3 and NO.
Pollution: Above 20ppm O3 is highly poisonous, and effects are observable around 0.1ppm. It oxidises much more readily than O2. Its issues in the troposphere include:
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It disrupts reactions in the body
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Irritant to eyes and respiratory system
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Toxic to plants leading to crop damage
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Degrades rubber and plastics
Solutions: To minimize the formation of O3 governments have set limits on the amount of exhaust emissions of both NOx and hydrocarbons. For the last 29 years cars have also been fitted with catalytic exhausts which convert NO to N2 and hydrocarbons to CO2.
Ozone in the Stratosphere
In the stratosphere ozone exists in equilibrium (formation – destruction) and absorbs harmful UV radiation.
Equilibrium & Absorption: Short UV waves (<240nm) act upon O2 gas forming O∙ free radicals which combine with O2 to form O3.
Some of these free radicals also react with OÂÂ3 molecules to form O2.
This O3 then absorbs longer UV waves (200-300nm) decomposing the O3 back to O∙ and O2.
These reactions all occur in an equilibrium, and UV is absorbed shielding the planet.
Benefits:
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Decreases sunburn and cancer caused by UV light.
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Protects eyes from UV radiation, decreasing the risk of cataracts
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Decreases risk of disease and illness, due to lowered immune response
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Less plant/crop damage, due to UV interference with photosynthesis
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Decreases damage to synthetic materials (brittleness and surface powder)
