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Causes: Ozone

Causes: ozone

(Image: NASA Earth Observatory )

Ozone (O3)


  • Ozone (O3) in the lower atmosphere (troposphere)(Fig. 1) is a greenhouse gas that absorbs some infrared energy from Earth, re-radiating it into the atmosphere. Due entirely to man-made emissions —including methane, nitrous oxide, and carbon monoxide—because it is a short-lived gas, its concentration varies enormously in different places, times, and seasons.
  • Ozone in the upper atmosphere (stratosphere)(Fig. 1), protects the DNA of plants and animals from harmful solar radiation. Without it, life on the surface of the Earth would be unable to exist. The Montreal Protocol to protect the ozone layer by phasing out the use of mad-made chemicals (CFCs) that deplete it. This has helped prevent large quantities of carbon dioxide in plants and soils from being released into the atmosphere, which would have resulted in even more warming:

“The avoided ultraviolet radiation and climate change also have co-benefits for plants and their capacity to store carbon through photosynthesis…we estimate that there could have been 325–690 billion tonnes less carbon held in plants and soils by the end of this century (2080–2099) without the Montreal Protocol (as compared to climate projections with controls on ozone-depleting substances).” – Young et al, 2021

  • This underscores the point that greenhouse gasses are not inherently ‘bad’. Rather, that human activities have and continue to change the balance of gasses in the atmosphere, causes a complex array of problems for life on Earth.
  • Unfortunately, in spite of the international Montreal Agreement to stop using ozone-depleting gasses that destroy ozone on the troposhere, the hole in the ozone layer over the Arctic grew to a record size in 2020 (top image).
Fig 1: The protective ‘Ozone Layer’ in the Stratosphere 20-30km above the surface of the Earth protects living organisms on the surface from harmful radiation. However, when ozone is down near the surface of the Earth in the Troposphere, it’s both a powerful greenhouse gas and pollutant. (Image: UCAR Centre for Science Education)

“Ozone is present in two different areas of the atmosphere and plays two different roles. It is produced naturally in the outer layers of the atmosphere (the stratosphere) very high above earth. This stratospheric ozone helps protect the planet from the Sun’s ultraviolet rays which can damage our skin and health. This ozone is typically known as the ozone layer.

“Although ozone is vital in the stratosphere, here at the Earth’s surface it is a pollutant which can damage our health and the environment.

“At the Earth’s surface, ozone is not directly emitted but is formed by reactions of other pollutants such as nitrogen oxides and volatile organic compounds (VOCs), and sunlight. This is known as a photochemical reaction and often produces photochemical smog.

“The primary pollutants are produced mainly from motor-vehicle emissions and other combustion sources, and industrial and domestic use of solvents and coatings.

“Auckland, Hamilton and Christchurch have the highest potential for ozone pollution.” – NZ Ministry for the Environment

References and further reading