Causes & Impacts of Ozone Depletion (Cambridge International IGCSE Environmental Management)

What causes ozone depletion?

• The stratosphere is the second layer of Earth's atmosphere and extends roughly 38 km(24 miles) between the **troposphere **and the mesosphere
• The highest concentration of ozone gas** is** within the first 3-20 km of the lower stratosphere (15-30 km above the Earth's surface)
• This layer acts as a natural 'sunscreen' for life on Earth by absorbing the majority of the sun's harmful ultraviolet (UV) radiation before it reaches the planet's surface

The stratosphere contains the ozone layer

Stratospheric ozone depletion

• Ozone can be destroyed more quickly than it can be created

• Some substances break down ozone even more than natural levels

  • These chemicals, known as ozone-depleting substances (ODSs), lower the amount of ozone in the stratosphere

  • The main ODS gases are hydrogen and nitrogen oxides and those containing chlorine

    • One chlorine atom can destroy over 100,000 ozone molecules before it is removed from the stratosphere

Human-produced ODSs

• Human-produced ODSs include

  • Aerosols containing chlorofluorocarbons (CFCs), such as sprays, foams, plastic manufacturing, deodorants and more

    • When released into the atmosphere during spraying, these substances can eventually reach the stratosphere and contribute to ozone depletion

  • Refrigerants in cooling systems, such as air conditioners and refrigerators, can leak and reach the stratosphere to contribute to ozone depletion

• Even though ODSs are produced and emitted at the Earth's surface, it can take from two to five years for the substances to reach and affect the stratosphere

Natural ODSs

• Natural processes, such as large volcanic eruptions, have an indirect effect on ozone levels

  • Mt. Pinatubo's 1991 eruption produced large amounts of aerosols(small particles) that increased chlorine's effectiveness at destroying ozone, although the effect was short-lived

• Polar stratospheric clouds (PSCs) form during the long, cold Antarctic winter

  • These clouds consist of tiny ice crystals in the stratosphere
  • Chlorine compounds, mainly man-made CFCs, are trapped within the ice crystals, forming chlorine reservoirs
  • During the Antarctic spring, the returning sunlight melts the ice crystals, releasing and reactivating the chlorine atoms
  • This causes rapid stratospheric ozone depletion and the formation of the 'ozone hole' over Antarctica

• Not all chlorine sources cause ozone layer depletion

  • Chlorine from pools, factories, sea salt, and volcanoes does not reach the stratosphere

• Because ODSs are stable and do not dissolve in rain, there are no natural processes that remove them from the lower atmosphere

Exam Hint Do not confuse global warming with ozone depletion.

Know the differences in causes and effects.

Ozone depletion is the thinning of the ozone layer and global warming is the raising of atmospheric temperatures.

Although the ozone layer is thinner, it does not allow increased levels of heat into the atmosphere, only ultraviolet light.

Impacts of ozone depletion

• Ozone depletion refers to the gradual thinning of the ozone layer in the Earth's stratosphere

• Stratospheric ozone depletion leads to increased levels of harmful ultraviolet (UV) radiation reaching the Earth's surface

• This negatively impacts human health, including

  • Higher UV-B radiation exposure significantly increases the risk of skin cancer, particularly melanoma, the most dangerous form
  • Increased UV radiation can lead to the development of cataracts, clouding of the lens in the eye
  • Excessive UV exposure can weaken the immune system, making individuals more susceptible to infections
  • Chronic exposure to UV radiation accelerates the ageing process of the skin, causing the breakdown of collagen and elastin fibres, leading to wrinkles, sagging skin and the development of age spots
  • Sunburn occurs when the skin is exposed to excessive UV rays that trigger an inflammatory response as a defence mechanism, indicating damage to the skin cells

• Ecosystems are damaged, affecting productivity

  • UV radiation can harm phytoplankton, the base of the marine food chain, impacting aquatic ecosystems
  • High UV levels can damage plant tissues, affecting crop yields and plant productivity
  • Disruptions in ecosystems due to UV damage can affect various species and alter food webs

• Clothing and construction materials exposed to UV rays are damaged and degraded

  • Fabrics, plastics, paints and building materials become brittle, faded or weakened, reducing their durability and lifespan
  • This reduces the material's structure and function and also its visual appeal

Exam Hint Don't confuse ozone depletion with the ozone hole.

Ozone depletion affects the entire Earth's stratosphere.

The ozone hole is an area of very low stratospheric ozone.

The hole is primarily over Antarctica in spring but can extend to South America and the Falkland Islands. The size and location of the ozone hole change depending on seasonal conditions.