Ozone hole

  • Image, ozone hole.

    Ozone is a gas that forms a naturally occurring layer in the upper atmosphere (stratosphere), protecting Earth from the sun’s ultraviolet (UV) light. The ozone hole is an area of reduced stratospheric ozone. It forms in spring over Antarctica because of ozone-depleting substances produced from human activities. The ozone hole has started to shrink due to the phase-out of these substances, and it is possible that it will cease to form by the middle of this century.

    The ozone hole does not have a large effect on the concentration of ozone over New Zealand. However, when the ozone hole breaks up in spring, it can send ‘plumes’ of ozone-depleted air over New Zealand. Reporting on the state of the ozone hole helps us understand the state of ozone concentrations globally.

    We classified Ozone hole as supporting information.

    Key findings

    The ozone hole reaches its maximum annual size, and minimum ozone concentration, during the Southern Hemisphere spring.

    In 2016:

    • the mean maximum size of the ozone hole was 20.9 million km2, a 21 percent decrease from its largest mean maximum size in 2006 (26.6 million km2)

    • the mean minimum ozone concentration was 124.3 Dobson units (DU), a 35 percent increase from the lowest mean minimum in 1994 (92.3 DU).

    Smaller ozone hole areas in 1988 and 2002 were a result of warmer than normal temperatures, caused by disturbed stratospheric weather conditions (NOAA, 2002).

     

    Figure 1 

    Image, Maximum ozone hole size in 2016, 28 September.

    Note: In 2016, the ozone hole reached a maximum size of 23.0 million km2 on 28 September.
    Figure 2

    Graph, Mean minimum ozone concentrations and mean maximum ozone hole sizes, 1979–2016.

    Note: The mean ozone hole size is for the period 7 September–13 October each year; the minimum mean ozone for the Southern Hemisphere is for the period 21 September–16 October each year.
    There is no ozone hole data for 1995 as NASA did not have a recording satellite in operation that year.

    Definition and methodology

    Ozone (O3) is a naturally occurring gas found in the stratosphere, 20–25 kilometres above Earth, in what is known as the ozone layer. The ozone hole is an area of reduced ozone (below 220 Dobson units (DU)) that forms over Antarctica. In winter, low temperatures over Antarctica form polar stratospheric clouds. Ozone-depleting substances react with these clouds, producing reservoirs of chlorine and bromine. Sunlight transforms these chemicals into forms that are destructive to ozone, so the ozone hole grows when the sun rises over Antarctica at the end of winter.

    Mean ozone refers to total column ozone, measured in DU. One DU represents the amount of ozone molecules needed to produce a 0.01mm layer of pure ozone. Minimum daily ozone (DU) is taken from annual measurements over the period 21 September to 16 October. The mean ozone hole area (million km2) is measured over the period 7 September to 13 October.

    In the 1970s, the US National Aeronautics and Space Administration (NASA, nd) began using satellite measurements to infer the depth and extent of the ozone hole. These estimates are validated against point observations, such as those from the Dobson spectrophotometer.

    Ozone-depleting substances are emitted through human activities, such as refrigerant and aerosol production. These substances can last up to several centuries, making their way up to the stratosphere and damaging the ozone layer. While the ozone hole does not directly affect ozone concentrations over New Zealand, when it breaks up in spring it can send ‘plumes’ of ozone-depleted air towards us. This briefly decreases column ozone levels by around 5 percent, about the same amount as normal daily variation (Ajtić et al, 2004). With the phasing out of ozone-depleting substances under the Montreal Protocol (UNEP, 2007), Antarctic ozone is expected to return to pre-1980 levels by around 2065 (UNEP, nd).

    The ozone hole also affects atmospheric circulation and has led to an increase in the occurrence of positive phases of the Southern Annular Mode climate oscillation (Thompson et al, 2011).

    Data quality

    We classified Ozone hole as supporting information.

    Relevance

       This supporting information is an indirect measure of the ‘Atmospheric properties' topic

    Accuracy

       The accuracy of the data source is of high quality. 

    See Data quality information for more detail.

    References

    Ajtić, J, Connor, BJ, Lawrence, BN, Bodeker, GE, Hoppel, KW, Rosenfield, JE, & Heuff, DN (2004). Dilution of the Antarctic ozone hole into southern midlatitudes, 1998–2000. Journal of Geophysical Research: Atmospheres, 109(D17).

    National Aeronautics and Space Administration (NASA) (nd). History of the ozone hole. Retrieved 20 July 2017 from http://ozonewatch.gsfc.nasa.gov.

    National Oceanic and Atmospheric Administration (NOAA) (2002). Unusually small Antarctic ozone hole this year attributed to exceptionally strong stratospheric weather, NOAA and NASA report. Retrieved from www.noaa.gov.

    Thompson, DWJ, Solomon, S, Kushner, PJ, England, MH, Grise, KM, & Karoly, DJ (2011). Signatures of the Antarctic ozone hole in Southern Hemisphere surface climate change. Nature Geoscience, 4(11), 741–749. http://doi.org/10.1038/ngeo1296.

    United Nations Environment Programme (UNEP) (nd). Montreal Protocol – Achievements to date and challenges ahead. Retrieved 5 June 2017 from http://ozone.unep.org.

    United Nations Environment Programme (UNEP) (2007). The Montreal Protocol on Substances that Deplete the Ozone Layer. Further adjusted by the Nineteenth Meeting of the Parties, Montreal, 17–21 September 2007. Retrieved from http://ozone.unep.org.

    Archived pages

    See Ozone hole (archived October 2017).

    Updated 19 October 2017

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