Atmosphere: Introduction
The atmosphere is the envelope of air surrounding the Earth. It consists primarily of nitrogen (78%) and oxygen (21%), with argon, carbon dioxide, trace gases and air pollutants making up the remainder.
There is no definite boundary between the atmosphere and outer space. The atmosphere becomes gradually thinner as altitude increases, and is usually described as a series of layers. Of particular importance to human health and the environment are the troposphere, the lowest layer of the atmosphere in which we live, extending to approximately 12 km, and the stratosphere, ranging from the top of the troposphere out to 30 km. The stratosphere contains the ozone layer, which provides protection from the Sun's ultraviolet radiation.
The atmosphere, essential for all life, has been generally taken for granted, although public perception of its importance has risen greatly in recent decades. Traditional concerns about local air pollution have given way to concern about the global issues of climate change, global warming and stratospheric ozone depletion.
It is now accepted that human activity has played major a role in changing the global climate by significantly altering the composition of the atmosphere, in particular through the rise in concentrations of greenhouse gases, which are responsible for temperature increases around the world.
Climate has a direct impact not only on the environment but also on social and economic aspects of life. Strategies to tackle climate change combine information on the historical variability of climate with modern scientific and technological methods that forecast future conditions within a risk management process.
Over the past five years the world has experienced four of the five hottest years on record. Since the previous reporting period Queensland has experienced increases in average, minimum, and maximum temperatures, 2005 being the hottest year since reliable records began. The past five years have also seen severe drought conditions in south-east Queensland, and the majority of the state has experienced below-average or well below-average rainfall. In response, the Queensland Government has released a strategy and action plans that contain policies and programs aimed at reducing greenhouse gas emissions, complemented by initiatives to help the state adjust to the potential environmental, social and economic impacts of climate change.
Ozone, from both natural and human sources, occurs in the atmosphere. At elevated levels in the troposphere, ozone is considered a pollutant. In the lower stratosphere, it acts to absorb the biologically harmful shorter wavelengths of ultraviolet (UV) radiation from the Sun. However, the stratospheric ozone layer has been severely depleted by the release of chemical compounds produced by human activities.
Depletion of this filtering layer reduces protection from solar UV radiation and occurs through reaction of the ozone with synthetic chemical compounds called ozone depleting substances, such as chlorine and bromine compounds. Stratospheric ozone has been declining over the past few decades, mostly as a consequence of large emissions of these ozone depleting substances. The decline has been particularly noticeable over the high latitudes of the Southern Hemisphere, and Australia has experienced high levels of UV radiation.
Global programs and treaties have been implemented to assist in protecting the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion. Monitoring confirms a decline from the peak values of ozone depleting substances in the early 1990s. Scientists predict that total ozone concentration is unlikely to decrease further, but will return to pre-1980 levels around the middle of this century in mid-latitudes and by 2060-75 over Antarctica. Climate change may delay the recovery process, so that high levels of UV radiation will continue to pose a risk to human health in Australia.
In contrast to the global issues of climate change and ozone depletion, air pollution has a direct local effect on health and the environment. Over the past quarter of a century, however, a continuing improvement in overall air quality has come about as a result of the implementation of strategies to reduce the emissions of key pollutants into the atmosphere.
Photochemical smog formed by the reaction of sunlight with primary pollutants has a detrimental effect on health and the environment. Over the past decade the control of motor vehicle emissions and bushfires has resulted in a steady decline in photochemical smog.
Increased coordination of hazard-reduction burning, controls on industrial activities and the move to green sugarcane harvesting have also resulted in an overall reduction in particle pollution and reduced visibility in Queensland. Exceedences of air quality standards occur mainly during uncontrolled bushfires.
Monitoring of toxic substances in the air, which provides information on potential health and environmental impacts, indicates that levels are well below national goals. The monitoring network also indicates that for the past decade there have been no exceedences of goals for carbon monoxide, lead and nitrogen oxides anywhere in the state, or for sulfur dioxide except in Mount Isa, where a major emitter operates.
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Last reviewed 11 May 2011
Last updated 8 February 2008