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

Urban Air Quality (continued)

Indicators of the condition of air quality (continued)

PM10 in urban areas [A Indicator 3.6]

  • Implications
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    The NEPM Standard for particulate matter with a diameter less than 10m (PM10) is 50/m3, averaged over one day. While industrial sources of PM10 depend on the exact mix of industry within the relevant urban area (Figure 100), 45% of PM10 can arise from coal combustion. Domestic sources are also significant, and 94% of the PM10 from these sources occurs during cooler months when wood is burnt for heating (Figure 101).

    Figure 100: Percentage of point source particle emissions by industry for south-east Queensland in 1993.

     Percentage of point source particle emissions by industry for south-east Queensland in 1993

    Source: based on Fig. 2-43 of EPAQ (1999a)

    Figure 101: Estimated particle emissions from domestic activities for south-east Queensland in 1993.

     Estimated particle emissions from domestic activities for south-east Queensland in 1993

    Source: based on Fig. 2-44 of EPAQ (1999a)

    Keywood et al. (2000) found that the primary composition of PM10 varied between Australian cities. In Sydney, Melbourne, Brisbane and Adelaide, it was composed of particles with two distribution peaks indicating that particles come from both combustion and mechanical processes, whereas in Canberra and Launceston, there was only one single fine particle mode indicating that the particles came predominantly from combustion.

    The 24-hour average PM10 levels in autumn and winter in the major urban areas of Australia peak at around 70 g/m3 or less (Figure 102). Higher values can be experienced in some regional centres due to the effect of woodsmoke (see Woodsmoke in Launceston).

    Figure 102: Maximum 24-hour PM10 concentration for selected Australian cities.

     Maximum 24-hour PM10 concentration for selected Australian cities

    Source: State and territory environmental authorities

    Instances of higher PM10 levels in the major urban areas can also occur during bushfires or controlled 'burn-off' of excess vegetation on the outskirts of urban areas. This is the cause of the high maxima and relatively high frequencies of exceedence of the Air NEPM PM10 standards for Sydney and south-east Queensland (Figures 102 and 103). The year 1994 was particularly fire-prone.

    Figure 103: Number of days during the year when the 24-hour average concentration of PM10 exceeded the Air NEPM level of 50 g/m3 in Australian cities.
    Negative values indicate zero exceedences. Zero values indicate no data.

     Number of days during the year when the 24-hour average concentration of PM10 exceeded the Air NEPM level

    Source: State and territory environmental authorities

    Figure 104: Annual maximum, 90th and 50th percentiles (median) and 10th percentile of maximum 24-hour PM10 concentrations from Perth (Caversham).

     Annual maximum, 90th and 50th percentiles (median) and 10th percentile of maximum 24-hour PM10 concentrations from Perth (Caversham)

    Source: WA Department of Environmental Protection

    The statistics underlying the PM10 concentration values (Figure 104) indicate that the median values (the 50th percentile) are well below the NEPM standard, as are the 90th percentiles. However, there are occasional years when the annual maximum can reach very high values.

    Implications

    As burning wood causes high PM10 levels, the Air NEPM standard indirectly restricts the number of times that fire-control authorities can 'burn-off' excess vegetation on the outskirts of urban areas. It is not yet clear whether such restrictions are a serious impediment to fire management. Episodic peaks in PM10 and PM2.5 concentrations occur during years when bushfires threaten Australian cities (e.g. in Figure 103 for south-east Queensland).