Quantification and Characterisation of Particulates from Australian Coal Mines: Towards Improved Emissions Estimation

Abstract

The community health effects associated with exposure to particulate pollution are well documented. Furthermore, the World Health Organisation has identified that no safe limit exists for community exposure to particulate pollution. In this context, policy and regulations associated with particulate exposure continue to reduce the allowable exposure thresholds both in Australia and overseas. This has consequences for industries such as mining, which is currently the primary source of industrial particulate emissions in Australia. Atmospheric dispersion modelling of particulates is a key tool used to inform environmental policy decisions. The accuracy of dispersion modelling has been found to be critically reliant on the quality of the input data, with the emission data inputs being a key variable. Particulate emission estimation methods currently adopted in Australia are of varying quality and only a limited sub-set of emission estimation methods are soundly based on local empirical data. The use of estimation methods developed for other regions has been shown to introduce significant uncertainty to emission estimation and pollution inventories. In the absence of appropriate local data, a number of the currently adopted particulate emission estimation techniques in Australia rely on methods based on data for other regions such as the United States. In addition, there is an almost complete absence of empirical data relating to PM10 and PM2 5 emissions from specific mining activities in Australia and overseas, and this a significant gap in our current understanding. The objective of this research programme is to characterise and define the appropriate emission rates for particulates for a range of activities at open cut coal mines in Australia. This objective was achieved by addressing a series of focus questions as follows: i. What are the key sources of emissions in Australian open cut coal mines? ii. What emission rates are currently used to define particulate emissions from mining activities at open cut coal mines, and how appropriate are they? iii. Is there significant variation in emission rates within mines due to local features of the mine or operations? iv. What are the appropriate emission rates to adopt for mines in different regions of Australia? To respond to these focus questions, the research has involved collection of source emission samples from a range of activities at Australian open cut coal mines. Three key approaches have been adopted. Firstly, PM10 and PM2 5 sampling at the boundary of mines and specific locations downwind of the mine has been completed. The samples were subsequently subject to chemical and visual analysis to identify particulate characteristics. Secondly, sampling of emission rates from erodible surfaces at coal mines has been completed using a portable wind tunnel methodology. Finally, sampling of a range of particulate sources in coal mines has been completed using a downwind sampling transect technique and subsequently applying Gaussian plume calculation techniques to determine the emission rate at the source. Practical components of the research have been completed in accordance with published peer reviewed methodologies and standard procedures. The guidance of regulatory agencies such as the United States Environmental Protection Agency in relation to developing a high-quality emission dataset has also been considered in developing the methodologies adopted for the field data collection and analysis. A range of quality assurance measures have been adopted. For field work and laboratory analysis these include pre and post calibration of field instrumentation, provision of field and laboratory blanks, temperature and humidity controlled analytical environments and selection of appropriate instrumentation and Quantification and Characterisation of Particulates from Australian Coal Mines: Towards Improved Emissions Estimation 4 methodologies. All data analysis has been subject to a quality assurance review of calculation methodologies and the overall results, to confirm the accuracy and validity of the datasets. The results of these research activities provide new knowledge in relation to a range of aspects of particulate emissions from Australian coal mines. The new knowledge can be summarised as follows: • At the boundary of a mine the percentage of PM2 5 particulates is close to 50 % lower than in the typical urban environment. However, these particulates have potential to be transported over long distances, hence the mine can remain a significant source of PM2 5 particulates in the region. • The size fractionation of particulate emissions from different regions can vary significantly, hence development of regional emission datasets is necessary. • New region and activity specific TSP and PM2 5 emission rates have been determined for Australian open cut coal mines • Emission estimation equations have been determined for calculation of TSP emission rates for wind speeds in the range 5 m s-1 to 12 m s-1. This will allow estimation of region-specific emission rates based on local meteorological conditions. • Typical haul route watering rates at Australian mines achieve a control efficiency of 27 %. The water application rate is well below the rate defined in the currently adopted emission estimation methodologies for achieving 50 % particulate emission control. • The US EPA moisture ratio approach for estimating haul route watering control efficiency is not representative of Australian conditions. • The research has confirmed the significance of local meteorological conditions for accurate estimation of mining particulate emissions for specific regions. • Surface crusting reduces particulate emissions from surfaces at wind speeds up to 6.7 m s-1. Overall, the research makes an original contribution to the current research relating to particulate emissions from open cut coal mines. The research expands on our current understanding of particulate sources in open cut coal mines with respect to size fractions, chemical and physical composition, and emission rates for a range of mining activities. The accuracy and applicability of the currently adopted haul route watering control efficiency calculation has been explored and found to significantly over estimate actual control efficiencies in practice for Australian coal mines. The research also validates the currently adopted open cut coal mining emissions estimation methods and provides hitherto unavailable empirical data relating to emission rates for particulates from a range of open cut coal mine sources. This provides a sound empirical basis for improving the accuracy of particulate emission estimation techniques for Australian open cut coal mines.