Open Cut » Environment
There is significant concern in the coal mining industry regarding the accuracy of air emissions estimation calculations/emissions inventories that are ultimately used to inform government air quality policy. In particular, the potential for overestimation of mining related particulate matter (PM) emissions that may in turn result in unwarranted political and regulatory attention. There is also concern in relation to how the accuracy of the emissions estimations is related to predicted concentrations.
Pacific Environment was awarded ACARP funding to apply material properties (silt and moisture) data, control efficiencies and emission factors collected in previous ACARP projects within coal mining particulate matter emission inventories. The updated emission inventories corresponded to those originally referenced within the Upper Hunter Air Quality Particle Model (UHAQPM). Updated emission inventories were then used within a regional atmospheric dispersion model for the Upper Hunter to establish if they improve model prediction.
Generally, the UHAQPM over predicted PM concentrations close to mining and under predicted further from mining, with sites where over predictions occurred attributed to the modelling of the coal mines.
The potential for PM over prediction in the vicinity of coal mines is clearly of importance to this project. An evaluation of the ability of the newly derived emission factors to improve model performance in areas where model prediction is critical, is a critical component of this work.
A review of the PM2.5 emission factors developed for ACARP project C23021 deemed them unsuitable for use in this project. As such this project has focussed on updating the PM10 emission factors, material properties and control measures.
To evaluate the model performance, the results from both the UHAQPM and this project were compared with observations from the Upper Hunter Air Quality Monitoring Network (UHAQMN).
Overall, it is difficult to draw a solid conclusion on whether the updated PM10 emission factors deliver more accurate predictions when compared with monitored data than the UHAQPM did using emission factors sourced from US EPA AP-42. This is due to too many other potentially confounding factors involved in this regional-modelling exercise, which was designed to assess all particulate emissions in the region, not just those generated by coal mining operations. The analysis of the effect of these factors was outside of the scope of the project.
Both this project and the UHAQPM have shown that typically better correlation is seen between the predictions and monitoring at sites where the meteorological data were included in the modelling. This is the very application under which the use of the revised emission factors would be applied (eg atmospheric dispersion modelling to assess impacts of current or proposed future mining operations).
It is recommended that the reliability of the ACARP emissions factors be explored further by completing a modelling assessment for a number of single mines, such as they would typically be applied in an impact assessment. This will allow site-specific meteorology to be included in the modelling, and more confidence can be had in the existing air quality.