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Where the dust settles: a spatial investigation of respiratory disease and particulate air pollution in the Tamar Valley (1992-2006)


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Jabbour, S 2007 , 'Where the dust settles: a spatial investigation of respiratory disease and particulate air pollution in the Tamar Valley (1992-2006)', Honours thesis, University of Tasmania.

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The detrimental health effects of particulate air pollution have been well established
through environmental health research worldwide. Fine or ‘respirable’ particulate
matter derived from combustion sources has been linked to both acute and chronic
respiratory and cardiovascular conditions, and premature death in the most susceptible
of a population. The Tamar Valley in northern Tasmania has a significant winter air
pollution problem. Launceston is the largest population centre in the valley (population
approx. 67,000) and despite its size this small city has regularly recorded the highest
levels of particulate pollution levels of any city in Australia. This is due largely to
complex geographic and climatic processes that support cold air drainage and the
formation of night-time temperature inversions in the valley over winter months.
Under these conditions ground temperature drops and air pollution becomes trapped at
ground level under a layer of dense cold air. Fine particulate matter from domestic
wood heating contributes to around 88% of particulate load in Launceston compared to
65% in other Australian cities. Concern has therefore been raised for the respiratory
health of Tamar Valley residents in recent years. Previous studies have assumed
homogeneity of pollution exposure, and disease risk, across the landscape. This
assumption is unrealistic, as recent research indicates that both the distribution of
disease and the dispersal of particulate air pollution exhibit considerable spatial
This is the first study to look in detail at the spatial relationships between particulate
air pollution and respiratory disease distribution in the Tamar Valley. Disease clustering
was investigated and various environmental processes were explored in detail to
explain the spatial disparity of disease distribution. Patterns of respiratory disease
occurrence in the Tamar Valley were investigated through spatial analysis of 15 years
(1992-2006) of de-identified hospital admissions records. Issues of confidentiality and
geoprivacy in spatial public health studies were discussed in detail. Spatial distributions
of Asthma, Bronchiolitis, Bronchitis and Chronic Obstructive Pulmonary Disease (COPD)
were explored individually and in combined form. Data were explored for annual
variations in disease distribution. This revealed that, while disease incidence generally
declined over the study period, this decline was most noticeable around George Town
in the north of the valley. Further analysis revealed little spatial variation in seasonal
spatial patterns of disease occurrence across the valley, though disease cases
generally were more numerous in winter. COPD incidence was found to be highly
clustered in a small number of address locations thought to correspond to nursing
homes and aged care facilities across the valley. It was therefore believed that COPD was more closely correlated with the locations of these facilities than with any
geographic or climatic processes. Three techniques for the detection of disease clusters
were applied (kernel density function, Getis Ord Gi* statistic and Kulldorff’s spatial
scan statistic). Areas around George Town and the North Esk valley east of Launceston
consistently showed elevated disease levels. However, considerable variation in the
reporting of ‘significant’ clusters was noted between methods, and also with the same
method at different spatial scales. Issues of statistical inference were therefore
Several ‘exposure surfaces’ were created to approximate the winter dispersion of
particulate air pollution in Launceston. Modelled air pollution concentrations were
derived from TAPM (The Air Pollution Model), a prognostic air pollution dispersion
model currently in use in Tasmania for environmental monitoring purposes. A digital
elevation model was also classified into terrain features that are known to accumulate
high levels of particulate pollution through the process of cold air drainage (i.e. lowlying
channels and river flats). Spatial relationships between disease incidence and
these air pollution ‘proxies’ were then explored in detail. Weak relationships were
found between disease incidence and terrain features representing small channel and
valleys. A ‘significant’ relationship was found between disease incidence and the valley
floor, though issues of statistical inference were again discussed in this context. Spatial
non-stationarity was detected in all relationships, indicating that global statistics
inadequately define these relationships. A strong inverse relationship was found
between modelled air pollution concentrations and disease incidence, indicating that
disease rates were generally higher in areas outside the modelled air pollution plume
derived by TAPM. TAPM concentrations were also found to closely mirror the underlying
population distribution. The inability of TAPM to adequately predict pollution levels in
areas outside major population centres, and various issues of socioeconomic
confounding were discussed as possible explanations for this finding.
Results generally revealed considerable variation in the spatial relationships between
disease incidence and air pollution proxies used in this study. These results argue
strongly for the spatial analysis of air pollution relationships to health outcomes, and
the continued refinement of methods. None of these findings could have resulted from
a purely temporal (non-spatial) investigation.

Item Type: Thesis - Honours
Authors/Creators:Jabbour, S
Keywords: spatial, respiratory disease, particulate air pollution, Tamar Valley, Tasmania, GIS, PM10
Publisher: Honours thesis, University of Tasmania
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