Modelling Fine-Particulate Dispersion over Short Time Spans from Open Cut Mining Activity

Emissions of dust, or particulate matter, into the atmosphere from various sources in the Australian environment are of considerable interest for health, environmental and aesthetic reasons. Particulate matter occurs in the atmosphere from two processes: direct release from a variety of surface sources (primary); and chemical reactions from gases and aerosols within the atmosphere (secondary). Surface sources produce mostly larger particles, and include industry, mining, volcanic emissions, agriculture, and wind-blown dust. Smaller particles are normally produced from a range of chemical reactions and from burning processes (NSW Mineral Council 2000). Ammonium sulfate is the most common secondary particulate in the atmosphere (King et al. n.d.).

Mining companies require accurate information about atmospheric dispersion of particulate matter from their operations for three reasons:

• To assist in making air pollution management decisions for existing mines;
• To help plan new developments; and
• To help establish a beneficial relationship between the company and the community.

Such information is most appropriate over a 24-hour time span, a period over which mining companies can practically adjust their operations to minimise particulate emissions. The community is also most aware of particulate emissions on this time scale. While mines can measure 24-hour concentrations of TSP and PM₁₀ at locations near the mine, these spot measurements cannot provide much information on the spatial distribution of particulate matter or the impacts of the dispersion on the community. In addition, spot concentrations do not distinguish between different possible sources of particulates.Proposed and existing mining operations therefore use models to estimate the spatial distribution of concentrations of, for example, PM₁₀ from their activities. These models estimate yearly average PM₁₀ adequately, but can often be seriously in error if applied to 24-hour time periods. Problems with the models are detailed in the final report.Regulators are increasingly expecting mining projects to predict short-term (24-hr) PM10 emissions, in response to increasing community concerns about episodic particulate pollution impacts. The inability of mining companies to properly predict short-term PM₁₀ concentrations creates considerable uncertainty about the impacts of mining activities on the air quality in their immediate surroundings and in neighbouring communities.The major purpose of this Australian Coal Association Research Program (ACARP) project is to develop a methodology to provide more accurate 24-hour spatial estimates of PM₁₀ and PM_2.5 around open-cut mining operations, by the application of existing proven dispersion models.