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
In this section
We live at the bottom of a shell of gas that surrounds our planet. Life-giving oxygen sustains us. A fragile layer of ozone some 15 to 30 km above us shields us from the harmful UV rays emitted by the sun. Greenhouse gases, such as water vapour and carbon dioxide, maintain an average surface temperature of a habitable 15C, rather than a frigid average of -18C that would prevail in their absence.
The earth's atmosphere (Figure 1) stretches hundreds of kilometres upwards, but most of the air resides in the troposphere (the lower 10-15 km) and much less in the stratosphere (above the troposphere to a height of about 50 km). Clouds and the other phenomena that make up our weather occur in the troposphere. The stratosphere is home to the ozone layer.
Figure 1: Diagram of the vertical structure of the atmosphere showing layers and temperature variations with height.
Source: Windows to the Universe at the University Corporation for Atmospheric Research (UCAR). & copy;1995-1999, 2000 The Regents of the University of Michigan; & copy;2000-2001 University Corporation for Atmospheric Research. All Rights Reserved
The main gases in the atmosphere are nitrogen and oxygen. Water vapour, argon, neon and helium are also present, as well as dozens of other gases of natural and human origin. Air also contains tiny solid and liquid particles (aerosol) such as dust, sea salt, volcanic ash, meteorite dust from space and material from bushfires. Table 1 lists the main components of the atmosphere and their abundances.
|Water||H2 O||0 to 4|
|Particles (dust etc.)|
A Present in urban air as a pollutant.
Source: after Crowder (1995).
At ground level, the amounts of nitrogen and oxygen in the air remain remarkably similar everywhere on the planet, comprising 78 and 21% of air, respectively. Table 2 presents typical concentrations of selected greenhouse gases and air pollutants in typical 'clean' air and urban air.
|Gas||Clean air||Urban air||NEPM ambient air quality standards A|
|Carbon dioxide (ppm)||360||360-600|
|Methane (ppb)||1 700||1 700-2 500|
|Nitrous oxide (ppb)||315||315-350|
|Carbon monoxide (ppm)||0.03-0.10||0.05-50||8 h: 9|
|Ozone (ppm)||0-0.035||0-0.20||1 h: 0.10
4 h: 0.08
|Sulfur dioxide (ppm)||1 h: 0.20
1 day: 0.08
1 y: 0.02
|Nitrogen oxides (ppm)||0.000005-0.00002||0.001-0.80||Nitrogen dioxide:
1 h: 0.12
1 y: 0.03
|Lead (g/m3)||0||1 y: 0.5|
|Aerosol (PM10B) (g/m3)||25||24 h: 50|
A Maximum acceptable level over the averaging period.
B PM10 aerosol are atmospheric particles with diameter
Source: CSIRO Atmospheric Research and NEPM (1998) Schedule 2.
Greenhouse gases, such as carbon dioxide and methane, exist in similar concentrations everywhere, although levels in the Southern Hemisphere are slightly lower than those in the Northern Hemisphere. These heat-trapping gases are long-lived and are spread around the planet. It is the increase in concentration of these gases due to human activity that gives rise to concerns about global warming and resulting climate change.
This Report also examines stratospheric ozone depletion, the other global-scale problem.
Emissions of pollutants from motor vehicles and industry can cause pollution problems in cities. Rural areas downwind of cities and large industrial plants may experience elevated pollution levels. Bushfires may generate fine particles, producing atmospheric haze. These problems on a local and regional scale, such as smog and haze, and their prevalence and effects in Australia, are addressed in this Report.
Australians are concerned about pollution of our air. Atmospheric issues feature strongly in a list of key environmental concerns to Australians, with air pollution remaining the environmental problem of greatest concern, with 29% nominating it at the top (ABS 1999). Ozone depletion (12%) and the greenhouse effect (9%) are also in the top 10 environmental concerns.
The greatest concern over air pollution occurs in New South Wales (35%), with people in Tasmania being least concerned (18%). The proportion of respondents nationally who nominated air pollution as a concern was markedly higher in metropolitan areas (34%) than in non-metropolitan areas (20%).
Air pollution has been the issue of concern to the greatest proportion of people, according to Australian Bureau of Statistics surveys conducted throughout the 1990s.
Despite concerns by Australians about air pollution and other atmospheric environmental problems, environmental protection expenditure by governments in these areas is lower than for any other environmental protection domain (ABS 2000). The Australian Bureau of Statistics compared expenditure on the following domains: air, biodiversity, soil, waste, water and 'other'.