Development of Australia-Specific PM10 Emission Factors for Coal Mines

Pacific Environment was awarded funding from ACARP for a study to review, update and further develop the emission factors that are used to quantify fugitive dust from open cut coal mining operations in Australia. In the context of the study fugitive dust was characterised as airborne particulate matter (PM) with an aerodynamic diameter of size equal to or less than 10 micrometres (μm) (PM₁₀).

The study focussed on the four main PM-generating activities at coal mies:

· Hauling of coal and overburden on unsealed roads;

· Bulldozer activity;

· Trucks loading/unloading coal and overburden;

· Wind erosion of exposed material (e.g. overburden dumps, coal stockpiles, exposed areas of land).

The main objective of the study was to deliver a new set of scientifically robust, Australia-specific PM₁₀ emission factors for three of the four main activities listed above (emission factors were not developed for wind erosion). It is anticipated that the use of these emission factors will reduce the uncertainty in the estimates of PM₁₀ emissions from open cut coal mines in Australia, thus contributing to the better understanding and management of such emissions.

There were seen to be significant positive synergies between the project's experimental design and the requirements of a Pollution Reduction Program placed upon all open cut coal mines in New South Wales (PRP U3). Accordingly, the study additionally completed an evaluation of best practice measures for the control of PM from the use of equipment on overburden and the loading and dumping of overburden (referred to as Coal Mine Pollution Reduction Program Condition U3 Assessment).

Methodology

The PM₁₀ emission factors have been determined from a series of field measurement campaigns at a total of six coal mines in the Upper Hunter Valley and Gunnedah Basin regions of New South Wales. Measurements were conducted between March 2013 and March 2015, and covered a range of seasonal and operational conditions. The conditions and operational activities at the six mines were considered to be representative of coal mines in Australia.

Emission factors for specific mining activities were determined.

In addition, bulk samples of the relevant source materials (e.g. haul road dust, coal stockpiles) were collected at the time of the PM₁₀ measurements, and the materials were subsequently analysed for silt content, moisture content, and threshold friction velocity.

As part of the Coal Mine Pollution Reduction Program Condition U3 Assessment, several potential measures for controlling the dust generated by overburden handling were investigated. Each technique was assessed for its practicability in a mining environment, and was quantitatively evaluated, where possible, in terms of its effectiveness.

The outcomes of this project have significantly advanced the understanding of and characterisation of appropriate emission factors for the quantification of fugitive dust from open cut coal mining operations in Australia.

· The study has led to several improvements in the understanding of PM emissions from coal mines. It has: Established new emission factors for hauling on unsealed roads. These emission factors are significantly lower than those calculated using the USEPA AP-42 emission factor equations.

· Established new emission factors for bulldozers operating on coal and overburden. The emission factor for bulldozer on coal is significantly lower than those calculated using the USEPA AP-42 emission factor equations

· Established new emission factors for coal and overburden handling (loading/unloading) activities. These emission factors are significantly lower than those calculated using the USEPA AP-42 emission factor equations.

· Provided quantitative control efficiencies for control measures on wind erosion sources.

· Quantitatively evaluated the efficiencies of various measures for controlling dust due to overburden handling activities.

· Produced a database of material characteristics for reference in the development of emission inventories for Australian open cut coal mines.

These data may be applied both in combination with existing techniques for emission quantification, as well as in their own right.

It is considered that the measured emission factors are for the most part significantly lower than those provided in the USEPA's AP-42 for a number of reasons, including:

· The underlying geology and road construction techniques are likely to differ at modern Australian mines compared with US conditions at the time of AP-42 development (data representative of 12 field test reports spanning the years 1979 to 1996).

· In New South Wales, high temperatures are typically combined with high humidity, which may not be the case for the US locations tested. Higher humidity will reduce the capacity to raise dust.

· Mine vehicles used in modern Australian mining are significantly higher (both in total height and space between road surface and bottom of vehicle body), have six wheels and are more optimised in terms of aerodynamic shape compared with historical equipment evaluated under the AP-42.

· Default emission rates for dozers have previously assumed relatively low moisture contents and relatively high silt contents compared with those measured as part of this study.

· Further, the silt content of overburden was measured as being significantly higher than coal, and threshold friction velocities support that overburden is more readily friable than coal.

The study outcomes reduce the uncertainty in the estimates of PM10 emissions from open cut coal mines in Australia. The information within this study is directly applicable to the development of atmospheric emission inventories and modelling studies, and contributes to the understanding and management of such emissions.