Open Cut » Environment
This project focuses on fine particles (PM10, PM2.5) and nitrogen oxides (NOx, NO2) in the Upper Hunter Region, NSW. It consists of four sections, each with specific goals:
- Section 1 describes a detailed sources and emissions inventory for the Upper Hunter Region, comparing the relative importance of emissions from open-cut mining to other sources;
- Section 2 describes an intensive instrument comparison analysis for PM10 and PM2.5 at Cheshunt Farm, between July 2003 and October 2003. The main purpose was to determine how well continuous monitoring results matched gravimetric standard results and to compare the reliability and quality of measurements from various instruments;
- Section 3 describes the results of Light Detection and Ranging (LIDAR) measurements at Cheshunt Farm in October 2003. The purpose was to determine the structure of the lower atmosphere, especially inversions and how these change over time.
- Section 4 describes the results of air quality modelling, using The Air Pollution Model (TAPM), for the year 2002, using the sources and emissions inventory information from Section 1.
The major outputs and findings of the Study are;
- NO2 and PM10 emissions inventories, based on the NPI but using activity data to produce hour-by-hour emission rates for a 12 month period, have been developed for the Hunter Valley Region. Even though this inventory does not include agricultural emissions, fugitives and bushfires (as there were no data available) it represents an important step in describing the temporal nature of PM10 emissions in the Hunter Region.
- The results of an intensive measurement campaign to compare a number of PM10 measuring instruments by running them side by side, showed that the TEOM was best correlated with direct High Volume Filter collections with a PM10 cut-off head. The next best instrument was the GRIMM sampler followed by one of the two DUSTTRACKS. However, for long term unattended field use of the instruments, other factors such as reliability and maintenance requirements are important and these factors need to be considered when choosing an instrument for field deployment.
- The LIDAR confirmed the behaviour of the development of the boundary layer while showing also that it was able to track dust plumes when they passed in the near vicinity. However, the LIDAR was restricted to heights above about 100m from the ground. This will limit its application in studies where the dust plumes from mining are contained within a narrow layer of the surface as occur during nighttime and early morning stable atmospheric conditions which give rise to the largest concentrations of PM10.
Section 1 Emissions Inventory Summary
The basis for the calculations of sources and emissions of PM10 and NOx in Section 1 was the National Pollution Inventory methodology, with support from an air emissions package developed by the Newcastle City Council. This project assessed emissions from mining operations, power stations, domestic sources, diesel rail engines, traffic, and biogenic sources (NOx only). There were three potentially important sources for which no information could be found: agricultural activities; bushfires; and fugitive emissions. Although the overall significance of these emissions is presently unknown, they are known to have significant short term regional impacts with effects that have been documented as far away as New Zealand. Despite these far ranging impacts there is scanty data available on these types of emissions.
For major emitters, such as open-cut mines and power stations, the NPI reports annual emissions totals. These were considered to be too coarse for detailed emissions evaluation and as an input base for modelling, which required hourly estimates. In order to develop hour by hour emissions rates, the open-cut mines were requested to provide details of emission from their activities for example periods (a week in summer and a week in winter). Unfortunately, such data were available only from some of the mines, depending on their internal monitoring of activities. Through a combination of actual data and proxy methods (fuel used, material moved for example), a representative estimate of PM10 and NOx emissions for the mines was determined.
Section 2 Instrument Comparison Summary
Gravimetric instruments were compared during the particle measurement study at Cheshunt Farm, a company owned property surrounded by mining activity. The instruments included High Volume Air Samplers (with and without an Anderson PM10 Head) and Ghent samplers from ANSTO. The continuous samplers were a Tapered Element Oscillating Microbalance (TEOM); a GRIMM laser sampler; and two DUSTTRACK laser photometers (DT1 and DT2). The continuous samplers were housed in an air conditioned, insulated shed, with sample lines extending in from the roof.
A major feature of this analysis was the difference in instrument reliability. The gravimetric samplers were operated for 24-hours every other day during the measurement period, and provided high reliable operation and results. The most reliable of the continuous samplers were the GRIMM and one of the DUSTTRACKs (DT2). The TEOM suffered from a seal leakage problem and became completely inoperable after 1350 on October 1 due to a lightning strike. DT1 had persistent calibration problems after 12 September.
Section 3 LIDAR Summary
The results of the LIDAR measurements showed a very detailed picture of the structure of the lower atmosphere at the Cheshunt Site, and how it changed over time. The LIDAR measured atmospheric structure above 100m in altitude, and was able to identify cloud layers and particle plumes from mining activity. The results verified that, for the most part, the atmosphere was very clean in the vicinity of the Cheshunt site “Textbook” variations of the diurnal changes in the near-surface boundary layer were observed, especially in the early morning transition period as the sun rose. These observations were best detailed when the synoptic situation was dominated by a high pressure system, with clear or partially cloudy skies, light winds, and an inversion present. The LIDAR was able to track the changes in inversion height over time.
Section 4 Air Quality Modelling
Modelling of the cumulative impacts of NO2 and PM10 for the year 2002 was performed with the air quality model TAPM using the NPI data from Section 1 of this report as the input data.
The modelling of NO2 concentrations, suggests that it is unlikely that the hourly average or annual NEPM goals for NO2 will be exceeded at any population centres in the region.
A comparison of model predictions for daily averaged PM10 with observational data showed either reasonable consistency between the two data sets or significant over-prediction for some sites. It became clear during the study that the model used, while providing advantages in terms of input data and physical robustness, did not provide adequate resolution of the different types of sources present at an open cut coal mine, which are important for predicting near field impacts.
To use the modelling approach taken in this work as a robust technique for environmental assessments of mine based emissions, an accurate description of the emission rates as a function of time of day and emission heights needs significantly further description and refinement. While the comparison between the model predictions and the observations were improved by adjusting the initial mixing of the mine emissions, it must also be noted that other contributors to PM10 for the region e.g. agricultural emissions, fugitives and bushfires, are represented in the observational data but were not included as sources for the modelled data.