Atmosphere Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
Stratospheric Ozone
This section reports on the environmental indicators listed below and are defined in Manton and Jasper (1998).
| Environmental Indicator | |
|---|---|
| A 2.1 | Concentration of ozone depleting substances in the atmosphere |
| A 2.2 | Stratospheric ozone concentrations across Australia |
| A 2.3 | Ultraviolet radiation flux at the surface |
| A 2.4 | Magnitude of Antarctic spring-time ozone hole |
| A 2.5 | National emission of ozone depleting substances |
| A 2.6 | Fulfilment of national responsibilities under the Montreal Protocol and associated agreements |
| A 2.7 | Public behaviour modification to protect against ultraviolet radiation |
| A 2.8 | Health effects linked to ultraviolet exposure |
| A 2.9 | Destruction of ozone depleting substances |
Introduction
Ozone is an important constituent of the atmosphere because it absorbs most of the harmful ultraviolet B (UV-B) radiation (280-320 nm) that emanates from the sun, preventing it from reaching the earth's surface. UV-B radiation causes several human health problems, some life threatening, and includes damage to the eyes, the immune system and the skin. UV-B radiation can reduce crop yields and cause changes in species composition of phytoplankton and zooplankton that affect marine food webs. UV-B radiation degrades synthetic polymers, such as plastics and surface coatings, and biopolymers, such as wood, paper, wool and cotton. Some chemical reactions taking place in the lower atmosphere can also be affected by UV-B radiation.
Ozone, unlike most other gases in the atmosphere, is found largely (90%) in the stratosphere, typically 15 to 30 km above the earth's surface (Figure 68), and is continuously being produced and destroyed by several chemical and photolytic processes. Net ozone depletion occurs when ozone loss exceeds ozone production.
Figure 68: The vertical distribution of ozone in the atmosphere at mid-latitudes.
Ozone vertical profiles are usually presented in units of partial pressure.
Source: after WMO
Ozone in the lower atmosphere (troposphere), and, in particular, ozone in cities and the regions, is discussed in Urban air quality and Regional air quality.
Ozone production occurs in the middle stratosphere when molecular oxygen is broken down by energetic UV radiation, forming atomic oxygen, which quickly reacts with molecular oxygen to form ozone. Ozone loss occurs largely in the lower stratosphere by UV photolysis and by reaction with atomic oxygen or ozone itself. The last two processes are very efficient in the presence of trace levels of nitrogen, hydrogen, chlorine and bromine oxides, which act as catalysts for ozone destruction.
The sources of increasing chlorine and bromine in the stratosphere are ozone-depleting substances that are released at the earth's surface. These substances break down in the stratosphere, releasing chlorine and bromine species that catalyse ozone destruction.