Air quality study in the lower Tamar Valley, Tasmania
Creators: name: Low, PS
Publisher: name: University Of Tasmania
Year: 2023

description: This study attempts to assess the air quality in the lower Tamar Valley where Bell Bay industrial area, one of the most important industrial centres in northern Tasmania, is located. The major sources of air emissions in the area include an aluminium smelter (Comalco Aluminium (Bell Bay) Ltd), a ferro alloys plant (Tasmanian Electro Metallurgical Co. Pty Ltd, or Temco), and a 2 x 120 MW oil-fired thermal power station. The effects and synergistic effects of the air emissions from these sources on the physical and human environment have been of concern to the local residents, particularly the dairy farmers and orchardists, over the years, yet very few air quality measurements have been made. Thus, an air quality study was undertaken from July 1982 to July 1984, with a view to drawing attention to, and enhancing the understanding of, some of the existing or potential air pollution problems in the area. The study, which is the most extensive and intensive one ever attempted in Tasmania, covered basically two major aspects: meteorological study and ambient air monitoring. A total of six Lambrecht Woelfle (model 1482) continuous recording anemometers was established between Low Head (near the coast) and Dilston (27 km SE of Bell Bay) at a height of 10-m. Data from December 1982 to November 1983 show that the wind field is strongly influenced by the topography of the valley, which generally has a NW-SE orientation. NW winds occurred most frequently in the afternoons, while the SE winds occurred most frequently in the mornings particularly at locations further up the valley due to the strong influence of the chanelling effects. However, different locations are also subjected to local katabatic winds which occurred most frequently from late night to early morning during the colder months. Of these, the most notable and important ones are the NE katabatic winds originating from the saddle between Mt George and the Tippogoree Hills, and the SW katabatic winds originating from one of the larger side valleys on the western shore, which could spread out and reach the industrial area as light W TO WNW flows if the main valley is calm. The frequency of occurrence of sea breezes was also investigated. They were found to enter the valley more frequently from the NW than N or NE directions. NW sea breezes occurred about one in every three days in summer, one in every five days in spring and autumn, and one in every seven days in winter. Sea breezes could flush and dilute the air pollutants from the Bell Bay industrial area, but could also carry them further up the valley. It is possible that some air pollutants carried off-shore in the morning could be returned to the valley a few hours later by the sea breezes. Atmospheric stability (based on the Pasquill-Turner stability classes) is estimated. In general, the winds with unstable classes A, B, and C occurred more frequently during the late morning to early afternoon for all stations, particularly in warmer months, while those with stable classes E, F, and G occurred more frequently from late night to early morning, particularly during the colder months. The neutral class D was most frequent for all months and could occur at all times of day. The spatial and temporal variations of the atmospheric stability are quite significant, suggesting that it is very much a function of locality and time. The frequency of occurrence of extreme stability conditions (class G) was higher whenever there were more light winds and in more sheltered regions. Limited tethered balloon soundings were performed within the planetary boundary layer from early evening to early morning in September and October 1982 so as to obtain the vertical profiles or structures of temperature and horizontal wind from which the diffusive power of the lower atmosphere may be derived. Many interesting meteorological phenomena, including surface and elevated inversions, wind shear effects, and upstream air blocking were observed in the Bell Bay industrial area. The morning surface inversion layers; sometimes associated with the occurrence of the wind speed maxima, were found to be able to develop up to a height of 200 to 300 m above the ground surface (about 40 m above sea level) of the valley. Elevated inversion at 425-530 m was also observed during a sea breeze evening. The wind field appears to be frequently influenced by the local katabatic winds and SE down-valley flows in the mornings at the lower level, and gradient winds 200 m above. NE winds channelled from the saddle between Mt George and the Tippogoree Hills could be blocked by the Asbestos/Dazzler Ranges on the western shore at an elevation of 100 m. Other aspects of meteorological study cover the daily weather observations, in particular, fog and haze smoke occurrences; horizontal. surface temperature mappings for investigating the heat island effects caused by the industrial sources; measurements of air temperature and humidity at the lower (10 m elevation) and upper (180 m elevation) levels for estimating the frequency of occurrence of surface inversions. The implications of air pollution in relation to all the above-mentioned meteorological factors are discussed. The ambient, air monitoring consisted of monthly sampling of bulk (wet and dry) atmospheric deposition, sampling of wet-only deposition based on event rains, regular sampling of suspended particulates, and monitoring of ambient SO\\(_4\\)\\(^{2-}\\), 0\\(_3\\), CO, and NO\\(_x\\) (no useful data were obtained for this part of study because of frequent malfunctions of the air analysers). The chemical compositions of the bulk deposition and suspended particulates samples were analysed using flame atomic absorption spectrometry (AAS). Chemical speciation of some selected precipitation samples was performed using Fourier Transform Infrared (FT-IR) on a trial basis, with some useful results obtained. Scanning electron microscopy (SEM) and Energy Dispersive Analysis of X-Ray (EDAX) were also used to characterise the chemical elements in some selected suspended particulates samples (using membrane filters) and monthly bulk deposition samples (using cellulose acetate filters). The mean annual fluxes of total insoluble dust ranged from 32.4 to 338.3 mg m\\(^{-2}\\) day\\(^{-1}\\). For trace elements Al (insoluble), F (soluble), Mn (total) and Fe (insoluble), the mean annual fluxes ranged from 445 to 5 638, 89 to 12 568, 38 to 3 676, and 392 to 1 534 ug m\\(^{-2}\\) day\\(^{-1}\\) respectively, with the lowest values being the intended 'background' levels. The fluxes of the elements are statistically correlated with each other, hence their sources identified (Al and F from Comalco, Mn from Temco). In general, they were much higher within 3 km of their respective sources. However, the air emissions from the industrial area could travel at least 10 km up the valley. The impact of the deposition rates of the trace elements on the local 'environment and ecosystems are difficult to assess, as no standards are available for comparison. A deposition rate of 100 ug m\\(^{-2}\\) day\\(^{-1}\\) for gaseous F (as HF for a 30 day period) is adopted by the South Carolina Pollution Control Authority, but the standard. may not be applicable to the lower Tamar Valley unless it was based on similar sampling and analytical techniques. The acidity of the bulk deposition and event rain samples were also investigated. The major acid-producing species, SO\\(_4\\)\\(^{2-}\\), mainly came from - the thermal power station, though there were some contributions from the metal-smelting industries. About 31% of the monthly bulk deposition samples and 76% of the event rain samples were acidic (pH &lt; 5.6). Locations near the thermal power station tended to have higher frequency of collecting acidic precipitation samples, though the air emissions from the 107 m stack could be transported by the fresh to strong westerly airstreams over the other side of the Tippogoree Hills before rainout or washout. The concentrations of total suspended particulates (TSP) and major trace metals (Al, Mn, Fe, and Cu) are calculated. At times the 24 hour concentrations of TSP exceeded 100 ug m\\(^{-3}\\), a standard adopted by Japan; while those of Mn exceeded 10 ug m\\(^{-3}\\), an ambient air standard recommended by many European countries. Ambient air standard for Al particulates is not available. Figures are only comparable if similar instruments, preferably with the same filters, or with filters of similar collection efficiencies, are used. With the practical and financial constraints, it was impossible to cover every aspect of air quality study in the lower Tamar Valley. Thus, recommendations for further research on meteorological study and ambient air monitoring are made. Finally, the major findings in this study are highlighted, and the major deficiencies in air pollution control in Tasmania are briefly discussed. It is suggested that public participation in the air quality management is necessary if future conflicts between government and industry on the one hand, and the general public on the other, are to be avoided.