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)
Ozone across regional airsheds [A Indicator 4.5]
Ozone is a strong oxidant, reacting with the tissues of the throat and lungs in animals, and the surfaces of leaves in vegetation (Table 4). The Air NEPM mandates a Standard for ambient ozone concentrations averaged over four hours (0.08 ppm, no more than one day per year) and averaged over one hour (0.10 ppm, no more that one day per year). Ozone is a photochemical product of VOCs and nitrogen oxides (see Introduction).
Regional ozone's precursor sources include vegetation, fires, industry and transport of urban emissions. A wide range of VOCs are involved. Biogenic emissions are a substantial percentage of the total VOCs active in regional ozone production. This is the case even for an airshed as urbanised as the Sydney basin where about 30% of the total VOC emissions for an average summer day in this region are biogenic (Carnovale et al. 1996). On a hot summer day (19-35C) in the sydney basin, biogenic emissions of VOCs were estimated to increase by about 100%.
Although the National Pollutant Inventory (NPI 1998, 2001) will soon be able to provide emissions information for Australia for the precursor pollutants, including some VOCs, in the interim it is useful to draw on the 1998 National Greenhouse Gas Inventory (AGO 2000) (for updated information see http://www.greenhouse.gov.au/inventory/index.html ). The estimates of emissions of VOCs for Australia since 1990, sector by sector (Figure 143), using a technique recommended by the Intergovernmental Panel on Climate Change shows that the total from all sources for 1998 is given as 1850 kt, only a little higher than in 1990 at 1760 kt. Notable are the estimated increases in 'Industrial Processes' and 'Agriculture' emissions of VOCs. The estimate for each year was based on the best available information at the time. Some of the increase may reflect new knowledge. A slow decline in 'All Energy' does not fully offset these increases, leading to an overall increase in emissions of VOCs for Australia over the past 10 years.
Figure 143: National emissions of volatile organic compounds (kt) by sector and year for Australia.
Estimates for 'Land Use and Forestry' were not applicable.
Source: AGO (2000)
The only routine ozone measurements made in Australia outside major cities occur in the Latrobe Valley, Newcastle and Wollongong. The number of days with one-hour ozone levels higher than 0.1 ppm are given in Figure 144. The peak recorded one-hour ozone levels (Figure 145) show that Illawarra experiences unacceptable ozone pollution by comparison with the Air NEPM. This is due mainly to interregional transport of ozone precursors from Sydney (see High regional ozone due to urban emissions).
Figure 144: Number of days one-hour ozone levels exceeded 0.1 ppm in regional New South Wales and Victoria.
Negative values represent zero exceedences.
Source: data from EPAs and EPAV (1990)
Figure 145: Maximum one-hour ozone concentrations measured in regional New South Wales and Victoria.
Source: data from EPAs and EPAV (1990)
An example of data for ozone in Dampier (WA), a growing industrial area in regional Australia centred on natural gas production (Figure 146) shows values as high as 0.06 ppm were measured towards the end of the dry season in 1999 and may have been related to bushfires.
Figure 146: Peak one-hour ozone levels measured throughout 1999 in Dampier (WA).
Source: Department of Environmental Protection, WA
Implications
There is growing evidence that precursor emissions from major urban regions are leading to high ozone in regional and rural Australia. Whether the anticipated decline in vehicle emissions will lead to improvement is unclear. Without significant reductions in per capita emissions of ozone precursors, the importance of regional ozone will increase as urban centres continue to grow. The effect of ozone on agriculture and native vegetation will increase. However, exposure will decrease since populations in rural areas are decreasing.
Although there is some evidence for the deleterious effect that regional fires can have on ozone levels in major urban areas, there are few data relevant to regional Australia.
High regional ozone due to urban emissions
One documented instance of high rural and regional ozone levels due to urban emissions occurred in Victoria on 18 March 1988. Aircraft measurements showed ozone levels of 0.14 ppm over Bacchus Marsh in air that had clearly originated over Melbourne 50 km to the south-east. Carras et al. (1988) estimated that an area of 600 km2 or more had ozone concentrations of 0.10 ppm or greater.
Numerical modelling for the Latrobe Valley Airshed Study (Manins 1988) found that observed ozone levels as high as 0.06 ppm could be explained by existing local sources. Interregional transport of precursors from Melbourne was able to explain the most extreme ozone levels (0.10 ppm or more) observed in the Valley, as well as lesser levels (Cope et al. 1988).
The Australian Air Quality Forecasting System (Cope et al. 1998; Hess et al. 2000) indicates substantial interaction of emissions from airsheds along the coast of New South Wales, reinforcing findings of the Metropolitan Air Quality Study (EPAN 1996), which ran from 1992 to 1994 (e.g. see Figure 147). Emissions from Sydney were predicted to transform into smog and be transported to regional airsheds at high concentrations.
Figure 147: Images of predicted one-hour ozone concentrations over New South Wales from the data analysis package of the Australian Air Quality Forecasting System.
Ozone generated from emissions from Sydney passing over the Illawarra is shown left. An instance of ozone generated from emissions from Sydney is shown entering the Upper Hunter Valley (right). In both cases, there are small regions where the predicted concentration exceeded 0.1 ppm (100 ppb). The white arrows indicate wind speed and direction; the colour shading of ozone concentration contours is keyed to the legend to the right in units of ppb (1000 ppb = 1 ppm).
Source: CSIRO data
Regional fires and high ozone levels
An analysis undertaken for the Urban Air Inquiry (ATSE 1997) concluded that fires contribute to many elevated ozone events. Figure 148 shows that average ozone levels in Melbourne (upper figure) and Brisbane (lower figure) are higher when there are bushfires in the region than on other occasions. The effect is more marked if only days conducive to ozone formation are selected.
Figure 148: Diurnal ozone variations on days with or without bushfires in the region for Alphington in Melbourne (upper figure) and Eagle Farm in Brisbane (lower figure).
Source: Katestone Scientific for Urban Air Inquiry (ATSE 1997).
Source: Katestone Scientific for Urban Air Inquiry (ATSE 1997)
There have been several measurements of elevated concentrations of ozone in fire smoke. On 18 October 1997, aircraft measurements were made of smoke from a large grass fire plume west of Katherine (NT). Photochemical reactions in the smoke raised the ozone concentration from a background level of 0.040 ppm to maximum values of about 0.100 ppm. The smoke was four hours old at the time of observation. Satellite measurements showed that smoke from the fire could be followed for the next five days as it drifted 2500 km west and over the Indian Ocean (Jensen et al. 2000).
Figure 149: Aircraft measurements of ozone concentrations in a smoke plume west of Katherine on 18 October 1997.
Flying north (left to right), the aircraft found high ozone levels in the smoke at an altitude of 2400 m. Further on, the smoke mixed to the ground, giving high ozone levels there.
Source: Tsutsumi et al. (1999)