University Of Tasmania
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Air pollution dispersion within the Tamar Valley

posted on 2023-05-26, 07:11 authored by Power, M
The Tamar Valley is a well-defined coastal valley, located in northern Tasmania (Australia). The valley has significant air pollution problems. At Bell Bay, approximately 5 km inland, there is a heavy industrial estate containing an aluminium smelter, a ferroalloy smelter, a medium density fibreboard plant and a thermal power station. The city of Launceston (pop. 72 000) is located 65 km inland, at the head of the valley. Launceston has a significant winter woodsmoke problem, regularly exceeding the 24-hour National Environment Protection Council (NEPC) goal for PM\\(_{10}\\) particles. Data from a network of 16 meteorological stations were combined to produce a climatology of the Tamar Valley, with many variables being mapped on a seasonal basis. The most important climatological parameters were amalgamated into an index of air pollution potential. A diagnostic wind field model, NUATMOS was used to model hourly wind fields for two-day periods each season under poor dispersion conditions. The modelled wind fields clearly showed the dominant flows occurring in the valley under anticyclonic conditions. Coastal westerlies and sea breezes are channelled inland along the northwest-southeast aligned valley. At night, there is a transition to down-slope and down-valley winds, which drain out of the valley. The CITPUFF Gaussian puff dispersion model was used to simulate dispersion of current winter woodsmoke emissions throughout the valley under poor-dispersion conditions. This model was used to help devise woodsmoke reduction strategies. The findings show that a 72 % reduction in woodheater numbers in Launceston is required to meet the NEPC particle goal. This goal is exceeded only in the Launceston region, and is chiefly caused by local sources, with only 4% of the particles modelled within Launceston originating outside of the city. Measured particle concentrations in Launceston have declined over the past few years, however additional measures are required if the NEPC goal is to be met. The introduction of reticulated natural gas to Launceston will allow the NEPC goal to be met if the city experiences an uptake to gas heating similar to that experienced by Canberra when gas was introduced. A more realistic scenario, with an uptake half that of Canberra's, would provide a significant reduction in PM\\(_{10}\\) concentrations, however this alone would not meet the NEPC goal. Banning open fires and non-certified woodheaters would come close meeting the goal. The goal is most likely to be met using a combination of reduction measures. Dispersion of SO\\(_2\\) from the combined Bell Bay industrial sources was modelled for each season, showing frequent exceedences of the NEPC hourly goal for SO\\(_2\\). The Bell Bay thermal power station was the dominant source, however this will shortly be converted from oil-fired to gas-fired operation. Modelled NO\\(_x\\) emissions from the gas-fired power station reveal a significant reduction in the number of exceedences.


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