You are here: Environmental reporting 
Atmosphere
Levels of stratospheric ozone
This indicator measures concentrations of stratospheric ozone over New Zealand. It is used to provide information on the condition of the ozone layer over mid-latitudes in the southern hemisphere.
Stratospheric ozone levels are measured over Lauder in Central Otago, as ‘total column ozone’: the total amount of ozone in a column of air from the earth’s surface to the top of the atmosphere. Data is used to illustrate the degree of ozone depletion, or how fast the ozone layer may be recovering at mid-latitudes in the southern hemisphere.
The levels of ozone-depleting substances in the atmosphere and levels of UV radiation are also discussed.
Did you know?
- Ozone is a gas present in trace quantities in the atmosphere.
- More than 90 per cent of ozone is found in the stratosphere, 20–25 kilometres above the earth, in what is known as the ozone layer.
- Ozone plays an important role in protecting the earth from the sun’s harmful effects.
- Although ozone is constantly created and destroyed in the stratosphere through natural processes, some chemicals increase the amount of ozone destroyed such as chlorofluorocarbons (CFCs).
Current situation and long-term trends
The average ozone concentration in 2006 was 298 DU (Dobson units), one of the five lowest levels on record. This can be explained by unusual stratospheric weather in that year.
Stratospheric ozone levels in New Zealand have changed considerably over time. Levels have stabilised in the last decade, reversing decreases in the 1980s and 1990s. A turning point in ozone concentrations may have been reached in 1997. Much of the stabilisation over the last decade can be attributed to reduced ozone depletion over Antarctica as a result of higher springtime polar temperatures and slightly reduced levels of chlorine and bromine in the stratosphere.
Average yearly ozone levels over New Zealand, 1970–2006
Notes:
(1) Five-year averages have been plotted to give an indication of trend in ozone concentration.
(2) DU = Dobson units.
Source: National Institute of Water and Atmospheric Research.
Levels of ozone-depleting substances in the atmosphere
Atmospheric levels of chlorine and bromine drive ozone depletion. Levels of these gases are expressed in units of equivalent effective chlorine, in much the same way as greenhouse gases are expressed in carbon dioxide equivalents.
Ozone levels track closely to average annual levels of chlorine equivalents, although there is a time lag. Levels of atmospheric chlorine and bromine have decreased over New Zealand since 1996 and over Antarctica since 2001. This decrease is primarily because of the global adherence by parties to the Montreal Protocol, which established targets for the reduction in the use of ozone-depleting substances.
Level of equivalent effective stratospheric chlorine, 1969–2006
Note: ppb = parts per billion.
Source: National Institute of Water and Atmospheric Research.
Ultraviolet radiation
Ozone depletion reduces the protective properties of the atmosphere and allows higher levels of UV radiation to reach the earth’s surface: when ozone levels are low, we experience a high UV index.
Changes in summertime ozone and peak ultraviolet index at Lauder, Central Otago
Notes:
(1) The upper panel represents changes in summertime ozone and the lower panel peak summertime UV index. The symbols show the average ozone and corresponding noontime measurement of the mean noon UV index for summer’s five highest UV index days in each month (15 days in total). The lines represent average summertime ozone calculated from satellite data, and a corresponding value for UV index calculated from these ozone values.
(2) DU = Dobson units
Source: National Institute of Water and Atmospheric Research.
What can you do?
- Planting trees removes carbon from the atmosphere, filters air, and prevents soil erosion.
- Compost your kitchen or garden waste – composting serves as a kind of carbon sink, storing carbon in the soil instead of in the atmosphere.
This information has come from the latest national state of the environment report Environment New Zealand 2007.
Return to main atmosphere page
Last updated: December 2007
