Location Darwin, in the monsoon tropical north of Australia, is uniquely placed to study particulates arising from biomass burning because of (i) a dry season climate with little variation in meteorological conditions over the austral winter months; (ii) predictable high frequency of landscape fires (bushfires) of variable intensity and extent with corresponding fluctuations in air quality; (iii) the absence of heavy industry and (iv) a single medical data registry. During the dry season approximately 96% of all atmospheric pollution consists of carbon particulates arising from bushfire smoke. As part of implementation of national environment protection measure for air quality the Northern Territory government commissioned a study to examine potential health impacts of the haze.
Methods An ecological study was conducted over the seven-month dry season in 2000. We examined the relationship between the mean atmospheric concentration of particles of 10 microns or less in aerodynamic diameter (PM10), per cubic meter, per 24-hour period and the daily number of presentations for asthma to the Emergency Department of Royal Darwin Hospital. Weekly general practice consultation rates for influenza-like illness, day of week, and school holiday periods were included as potential confounders. Negative binomial regression was used to compare exposure and outcome measures.
Results There was a significant increase in asthma presentations with 10 µg m-3 increases in PM10 the adjusted incidence rate ratio (IRR) being 1.26 (95% CI 1.12-1.41, p < 0.001). The greatest association occurred on days in which the PM10 was above 40 µg m-3 (adjusted IRR 2.47 [95% CI 1.21-5.01]), compared with days when PM10 levels were less than 10 µg m-3.
Conclusions This study found a strong association between asthma and increasing levels of atmospheric particulates, even at low concentrations relative to current air quality standards. However it was of small scale, did not adjust for mould and pollen counts, meteorological conditions or autocorrelation of data. A more comprehensive trans-disciplinary research program, including landscape ecology, meteorology, atmospheric chemistry and epidemiology, is now underway with the goals of improving human health outcomes, reducing of smoke pollution to below the current national air pollution guidelines and identifying ecological and meteorological factors, such as fuel types and atmospheric inversions, that cause high concentrations of particulates.
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