Roles of Ozone

Monitoring and Management‎ > ‎4. The Atmosphere‎ > ‎ ‎

Describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant

• Ozone is found at very low levels in the lower atmosphere (0.02 ppm in clean air).
• The formation of ozone through the interaction between sunlight, hydrocarbons and nitrogen oxides can lead to higher concentrations in the lower atmosphere or troposphere.
• Ozone is poisonous to humans (as well as most other organisms), with its effects in larger than normal concentrations including:
  • Breathing problems.
  • Aggravation of respiratory problems.
  • Headaches.
  • Fatigue.
  • Death (in high concentrations).

• Ozone exists at much higher levels in the upper atmosphere or stratosphere (ranging from 2 ppm to 8 ppm in the stratosphere), where 90% of the atmosphere’s oxygen is found.
• In the upper atmosphere both oxygen gas and ozone gas absorb different parts of the ultraviolet radiation range in a cycle of ozone formation and decomposition:
• • Oxygen absorbs high energy ultraviolet radiation as part of the ozone formation process:

• • Ozone absorbs medium energy ultraviolet radiation as part of the ozone decomposition process:

• • In both of these sets of reactions, the second reaction is exothermic, which accounts for the increasing temperature in the stratosphere.
• Thus, the ozone layer acts as a radiation shield in the upper atmosphere by absorbing medium and high energy ultraviolet radiation.

Distribution of atmospheric oxygen