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Background: This paper examines the short-term health effects of air pollution on daily hospital admissions in Australian cities (those considered comprise more than 50% of the Australian population) for the period 1996-99. Methods: The study used a similar protocol to overseas studies and derived single city and pooled estimates using different statistical approaches to assess the accuracy of the results. Results: There was little difference between the results derived from the different statistical approaches for cardiovascular admissions, while in those for respiratory admissions there were differences. For three of the four cities (for the other the results were positive but not significant), fine particles (measured by nephelometry--bsp) and nitrogen dioxide (N[O.sub.2]) have a significant impact on cardiovascular admissions (for total cardiac admissions, RR=1.0856 for a one-unit increase in bsp ([10.sup.-4].[m.sup.-1]), RR=1.0023 for a 1 ppb increase in N[O.sub.2]). For three of the four cities (for the other, the results were negative and significant), fine particles, N[O.sub.2] and ozone have a significant impact on respiratory admissions (for total elderly respiratory admissions, RR=1.0552 per 1 unit ([10.sup-4].[m.sup.-1]) increase in bsp, RR=1.0027 per 1ppb increase in N[O.sub.2], RR=10014 per 1 ppb increase in ozone for elderly asthma and COPD admissions). In all analyses the particle and N[O.sub.2] impacts appear to be related. Conclusions: Similar to overseas studies, air pollution has an impact on hospital admissions in Australian cities, but there can be significant differences between cities.

Objective: To examine the short-term health effects of air pollution on daily mortality in four Australian cities (Brisbane, Melbourne, Perth and Sydney), where more than 50% of Australians reside. Methods: The study used a similar protocol to APHEA2 (Air Pollution and Health: A European Approach) study and derived single-city and pooled estimates. Results: The results derived from the different approaches for the 1996-99 period showed consistent results for different statistical models used. There were significant effects on total mortality, (RR=1.0284 per 1 unit increase in nephelometry [[10.sup.-4].[m.sup.-1]], RR=1.0011 per 1 ppb increase in N[O.sub.2]), and on respiratory mortality (RR=1.0022 per 1ppb increase in [O.sub.3]). No significant differences between cities were found, but the N[O.sub.2] and particle effects may refer to the same impacts. Meta-analyses carried out for three cities yielded estimates for the increase in the daily total number of deaths of 0.2% (-0.8% to 1.2%) for a 10 [micro]g/[m.sup.3] increase in P[M.sub.10] concentration, and 0.9% (-0.7% to 2.5%) for a 10 [micro]g/[m.sup.3] increase in P[M.sub.2.5] concentration. Conclusions: Air pollutants in Australian cities have significant effects on mortality.

This paper presents a summary of the key findings of the special issue of Atmosphere on Air Quality in New South Wales and discusses the implications of the work for policy makers and individuals. This special edition presents new air quality research in Australia undertaken by (or in association with) the Clean Air and Urban Landscapes hub, which is funded by the National Environmental Science Program on behalf of the Australian Government's Department of the Environment and Energy. Air pollution in Australian cities is generally low, with typical concentrations of key pollutants at much lower levels than experienced in comparable cities in many other parts of the world. Australian cities do experience occasional exceedances in ozone and PM2.5 (above air pollution guidelines), as well as extreme pollution events, often as a result of bushfires, dust storms, or heatwaves. Even in the absence of extreme events, natural emissions play a significant role in influencing the Australian urban environment, due to the remoteness from large regional anthropogenic emission sources. By studying air quality in Australia, we can gain a greater understanding of the underlying atmospheric chemistry and health risks in less polluted atmospheric environments, and the health benefits of continued reduction in air pollution. These conditions may be representative of future air quality scenarios for parts of the Northern Hemisphere, as legislation and cleaner technologies reduce anthropogenic air pollution in European, American, and Asian cities. However, in many instances, current legislation regarding emissions in Australia is significantly more lax than in other developed countries, making Australia vulnerable to worsening air pollution in association with future population growth. The need to avoid complacency is highlighted by recent epidemiological research, reporting associations between air pollution and adverse health outcomes even at air pollutant concentrations that are lower than Australia's national air quality standards. Improving air quality is expected to improve health outcomes at any pollution level, with specific benefits projected for reductions in long-term exposure to average PM2.5 concentrations. [ABSTRACT FROM AUTHOR]