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)

Sulfur dioxide across regional airsheds [A Indicator 4.1]

Sulfur dioxide attacks sensitive tissues in the throat and lungs, as well as in vegetation (Table 4). Sulfur dioxide is usually associated with combustion particles, and was once a major health concern in big cities. Most of regional and rural Australia is unaffected by sulfur dioxide pollution except for centres of substantial industrial operations, generally involving mineral extraction or processing, that may at times experience sulfur dioxide pollution. Valuable mineral elements in Australia are generally found in refractory sulfide ores. The common extraction processes lead to generation of copious quantities of sulfur dioxide (e.g. in Kalgoorlie, the roasting of 1 t of iron sulfide ore leads to the generation of 600 kg of sulfur dioxide and 40-80 g of gold). Another significant source of sulfur dioxide is thermal power stations burning black or brown coal, although coals in Australia generally contain little sulfur. Regions of interest due to sulfur dioxide emissions are shown in Table 30.

Table 30: Estimated annual emissions of sulfur dioxide (SO₂) from major sources in Australia Major city airsheds
are Brisbane, Sydney, Perth, Port Phillip Region and Adelaide (see *Urban air quality*).
Location	SO₂ emissions (kt/y)	Source type
Mount Isa and Mica Creek (Qld)	500 (1985)^A, 491 (1998)^{B, C}, 663 (2000)^C, 333 (est. 2001)	Copper, lead smelters, power generation
Kalgoorlie (WA)	372 (1995)^A, 206 (1998)^D	Nickel, gold processing
Hunter Valley (NSW)	105 (1993)^A, 109 (2000)^C	Power generation and aluminium smelting
Central Coast (NSW)	110 (2000)^C	Power generation, aluminium smelting, metal processing
Mount Piper (NSW)	39 (2000)^C	Power generation
Gladstone (Qld)	80 (1996)^A, 32 (2000)^C	Power generation and aluminium smelting
Tarong, Stanwell, Raceview, Callide, etc. (Qld)	88 (2000)^C	Power generation and nickel processing in other Queensland centres
Port Pirie (SA)	53 (1994)^A, 58 (1998)^E, 48 (2000)^C	Lead smelting
Port Augusta (SA)	12 (2000)^C	Power generation
Anglesea Power Station & Point Henry and Portland Al smelters (Vic.)	33 (2000)^C	Power generation and aluminium smelting
Latrobe Valley (Vic.)	47 (1984)^A, 100 (1999)^F	Power generation
Collie (WA)	36 (1985)^A, 52 (1998)^C	Power generation, alumina
Nhulunbuy (NT)	31 (1985)^A, 28 (2000)^C	Alumina refining
Brisbane (SE Qld)	20 (1993)^A, 16 (2000)^C	Power generation, oil refining, shipping and motor vehicles
Sydney region (NSW)	20 (1993)^A, 15 (2000)^C	Oil refining, mineral processing and motor vehicles
Perth-Kwinana (WA)	18 (1992)^A, 19 (1999)^G	Power generation and oil refining
Port Phillip Region (Vic.)	15 (1990)^A, 17 (1996)^H	Oil refining, chemical and metal processing
Adelaide Region (SA)	3 (2000)^C	Oil refining and power generation
Total - latest estimated	1619 (~1992-1995), 1260 (est. 2001)

^A NEPC (1998) Impact Statement, Table 11.1;
^B MIM (1999);^C NPI (1998, 2001);
^D Annualised DEP (1999) NPI Trial for Kalgoorlie;
^E Pasminco (2000b);
^F EPAV emissions data;
^G DEP (2000);^H EPAV (1998).

Source: as listed in the table.

Mount Isa Mines has consistently been the biggest source of sulfur dioxide in Australia. A new sulfuric acid plant built by Western Mining Fertilisers on the Mount Isa Mines lease began operation in 2000. When fully commissioned, the emissions of sulfur dioxide from the site are expected to be about 330 kt/year. This is a reduction of over 50%. However, sulfur dioxide emissions at Mount Isa will still substantially exceed those at Kalgoorlie.

Ambient monitoring data for several regional centres (Figures 127 and 128) show a dramatic reduction in the number of exceedences of the current Air NEPM (see Tables 2 and 18) in Kalgoorlie (Figure 127) to zero in 1998 and one in 1999 (although there were eight reported exceedences in 2000). This reduction is a result of the commissioning of a sulfuric acid plant by WMC Nickel in October 1996 and the operation of a predictive shutdown control strategy managed by the gold and nickel producers. The strategy is similar to the one operated by Mount Isa Mines.

Figure 127: Number of days when one-hour sulfur dioxide exceeded Air NEPM (0.2 ppm, 1 day/year).
Negative values represent zero exceedences. For Gladstone and the Latrobe Valley, there were zero exceedences for the whole period.

Source: Data from State EPAs, WA DEP and WA SoE (1998)

Figure 128: Highest one-hour averages of sulfur dioxide since 1985 in regional centres of Australia.
Lower Hunter from 1992; Port Pirie from July 1995.

Source: Data from State EPAs, WA DEP

In Mount Isa town, the mine operates a control strategy that involves shutting down production if an impact on the town is predicted. Although this strategy is proving successful in maintaining the concentrations in the town below the company's licence levels, sulfur dioxide levels and exceedence frequencies have been substantially higher than the Air NEPM Standard (Figures 127 and 128). The new acid plant is greatly reducing (by up to 80%) sulfur dioxide emissions from the Mount Isa Mines copper smelter stack. However, ground level concentrations of sulfur dioxide in Mount Isa are not expected to change substantially from the levels of recent years (MIM 1999).

Data from Gladstone and the Lower Hunter data from 1992 show no exceedences of the Air NEPM, and Latrobe Valley data also show no exceedences.

The copper smelter at Port Kembla was the source of very high ground level concentrations of sulfur dioxide (Bell 1965; see also Lead across regional airsheds). The smelter commenced recommissioning in 2000 with a rebuilt plant including a new sulfuric acid processor to remove much of the sulfur dioxide from the emissions. Port Kembla Copper Pty Ltd have reported some monitoring data (see http://www.pkc.com.au ).

In Port Pirie, data for recent years show that extreme levels of sulfur dioxide in this South Australian town are too high by comparison with the Air NEPM.

Implications

Emissions of sulfur dioxide in Australia (Table 30) have reduced by almost one-third over the past five years. This reduction has occurred despite a substantial increase in the amount of mineral processed. A major reason for this improvement has been the adoption of plant to convert sulfur dioxide to sulfuric acid instead of emitting it to the atmosphere. The benefit can be seen in reduced ground level concentrations (Figure 128) and in the fewer days when levels were above the present Air NEPM (Figure 127).

Taking the Air NEPM as the benchmark for acceptable air quality, it appears that there are only three regional areas of concern in Australia. Sulfur dioxide concentrations in Kalgoorlie have been close to or better than acceptable for the past four years and may even improve, as long as the industry and regulator continue to be as diligent as at present. In Mount Isa, it appears that the mine can continue to meet its present licence with their predictive control strategy. However, meeting the one-hour Air NEPM Standard is evidently a much bigger challenge even with full production by the WMC Fertiliser sulfuric acid plant. The third region of concern is Port Pirie, where maximum concentrations are presently unacceptable.

Figure 129: Annual average sulfur dioxide concentrations in regional centres of Australia.
For Port Pirie, CSIRO used annual emissions data (see Table 30) and a numerical model to estimate annual averages in the town.

Source: Data from State EPAs, WA DEP and CSIRO

A graphical history of air pollution in Kalgoorlie

In Kalgoorlie, monitoring at the hospital commenced in 1982. Figure 130 shows the long time-series of measurements of maximum one-hour average sulfur dioxide levels for each month, with major events indicated. The most significant events that led to improved air quality were the closure of the three roasters along the 'Golden Mile' and replacement with the Gidji roaster in 1990, and the commissioning of the sulfuric acid plant at the nickel smelter in 1996. There have been no exceedences since 1997 of the Air NEPM at the Kalgoorlie Hospital.

Figure 130: Maximum average hourly sulfur dioxide levels at Kalgoorlie Hospital and significant events since 1985.

Source: data from DEPW

Acid deposition in Australia

Sulfur dioxide and nitrogen oxides emitted into the atmosphere are transformed by natural chemical processes into trace levels of sulfuric and nitric acids and later into aerosol. The acids, gases and their aerosol products return to the earth's surface by wet deposition (in rain) and by dry deposition (contact with surfaces). Environmental damage can occur when the extra acid added to surface soil or water exceeds the capacity of ecosystems to accommodate it.

Enhanced by a recent major investigation around Mount Isa (Ayers et al. 1999), the present state of knowledge of acid deposition in Australia is summarised in SoE (1996, p. 5.32):

Acid deposition is not a widespread problem here, as sources are generally geographically isolated from each other.
Unlike many European countries, Australia is not subjected to transboundary transport of emissions from neighbouring countries.
The major deposition process here is dry deposition of SO₂ .
Nevertheless, Australia has some significant individual sources and regional sources of acid-precursor emissions, and excessive acid deposition in the regions surrounding these sources is a possibility.
There may be small areas of poorly buffered soils (soils unable to accept acids without change to acidity) in Australia that could be easily acidified.

Figure 131 shows the range sensitivities of soils to acidification across Australia.

Figure 131: Sensitivity of Australian soils to acidification.

Source: from Stockholm Environment Institute, accessed 4 January 2001
(see http://www.york.ac.uk/inst/sei/rapidc2/sens/sensmaps.html )

Acid deposition downwind of Mount Isa

CSIRO and Mount Isa Mines (Ayers et al. 1999) measured atmospheric sulfur dioxide concentrations at 40 sites in the region surrounding Mount Isa to a distance of more than 100 km from the smelting complex for 12 months (September 1997 to September 1998). Atmospheric concentrations of other gases and aerosol were obtained, as were soil and surface water samples.

Based on the measurements and far-field dispersion modelling of the plume from the smelter, CSIRO calculated that 54% of the MIM sulfur emissions were deposited in Australia, with 46% advected offshore. Mount Isa is a long way from the most common exit point for the plume from the continent (near Darwin). By then, dispersion lowered the modelled sulfur dioxide, aerosol sulfate and rainwater sulfate component concentrations to levels significantly below the 'natural' background levels. For sulfur dioxide, the 'natural' background level was estimated to be 0.8 ppb (similar to the measurements (1 ppb) out to 160 km shown in Figure 132).

Over the Australian continent, surface deposition was dominated by dry deposition of sulfur dioxide (51%), followed by dry deposition of aerosol sulfate (30%) with wet deposition of sulfate being the smallest deposition component (19%).

Soil changes of potential biological significance due to deposition of sulfur were restricted to downwind distances of about 5 km for the top 100 mm (surface) layer of soil. Soil changes were undetectable in the 10 to 20 cm layer. The change of soil pH with distance is shown in Figure 132.

Figure 132: Trends in surface soil pH, sulfate and sulfur dioxide with distance to the north-west of Mount Isa.
Hydrogen ion concentration (H⁺) and sulfate refer to surface soil concentrations at sites with pH<5, SO₂ refers to 12 month average concentrations at these sites. The data at 160 km emphasise local natural variability of soil properties, showing an acidic soil even though this site was remote from Mount Isa.

Source: From Ayers et al. (1999)