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
Regional Air Quality (continued)
Meteorological conditions that exacerbate air quality problems [A Indicator 4.10]
Although some progress has been made in estimating the frequency of meteorological conditions that exacerbate air pollution in the major cities of Australia (ATSE 1997, see Examples of meteorology conditions that exacerbate air quality problems), there appear to be no data for recent years and none for regional Australia.
A combination of low rainfall and strong winds can lead to high regional air pollution such as wind-blown dust. If temperatures are high, the result can be bushfires that in turn can cause high levels of pollution such as particles, nitrogen oxides, ozone and other gases. Australia is particularly susceptible to this combination of conditions (see Drought related impacts and the Land Theme Report). Other conditions that exacerbate air pollution include trapping of pollutants close to the ground in atmospheric inversions at night, and mixing of plumes to the ground at high concentrations in daytime convective conditions.
Examples of meteorological conditions that exacerbate air quality problems
The most devastating fires in Australia in recent years occurred during periods of strong hot winds originating at the centre of the continent after a prolonged period of low rainfall. Figure 126 shows weather conditions conducive for fires in south-east Australia (top); and in the Sydney region (middle). The lower map is an example of a summer high pressure system over the centre, leading to strong winds from the inland over the southern parts of western Australia (BoM 1995; Trevitt et al. 1995).
Figure 126: Meteorological conditions for (top) Ash Wednesday, 16 February 1983; (middle) the Sydney Fires, January 1994; and (bottom) fires in the Perth region, April 1978.
Source: BoM (2003c)
A second common set of weather conditions that exacerbates air pollution occurs in most parts of Australia. On cold nights with little wind, a temperature inversion often causes smoke and other air pollution to accumulate overnight close to the ground. In winter in valleys in southern Australia, these stagnant conditions can last for days.
An example of pollution trapping is in the Tuggeranong Valley, ACT, in winter. With wood-burning fires operating at night, smoke is trapped below the warmer inversion layer. Inversions break down when the sun rises and heats the ground. Trapping of pollution in the Valley is a noticeable problem on many winter nights: visibility is reduced and the smell of smoke fills the air. Carbon monoxide levels may also be high (ACT 1997).
The third important weather condition associated with substantially elevated concentrations of air pollutants occurs during days with intense solar heating. Strong vertical currents, driven by transfer of heat from the hot ground to the air, can mix even high plumes from tall stacks to the ground rapidly for several minutes at a time. The plumes are said to loop in the air, alternately rising and falling in the air currents, leading to frequent high ground-level concentrations (see photograph).
A looping plume at Port Pirie (South Aust.) in strongly convective conditions.
Source: CSIRO