Skip to content

Causes: Ozone

Causes: ozone

(Image: NASA Earth Observatory )

Ozone (O3)


  • Ozone (O3) in the lower atmosphere (troposphere)(Fig. 1) absorbs some infrared energy from earth, re-radiating it in the atmosphere. It’s short-lived and entirely due to man-made emissionsincluding methane, nitrous oxide, and carbon monoxidemostly pollution in cities, so its concentration varies enormously in different places and over different times and seasons.
  • It’s important to note that while ozone is a greenhouse gas in the lower atmospher, without ozone in the upper atmosphere (stratosphere)(Fig. 1), the DNA of plants and animals would be so damaged that life on the surface of the Earth would be unable to exist. Unfortunately, in spite of an international agreement to stop using ozone-depleting gasses, the hole in the ozone layer over the Arctic grew to a record size in 2020 (top image).
  • This underscores the point that the location of where some gasses are in the atmosphere plays a pivotal role in calculating their global warming potential. It also underscores the point that greenhousse gasses are not in inherently ‘bad’, but too many (or too few) in the wrong location because of human activities, causes problems for life on Earth.
Fig 1: The protective ‘Ozone Layer’ in the stratosphere 20-30km above the surface of the Earth. When ozone is in the troposphere down near the surface of the Earth, it is 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