Two decades of trends in urban particulate matter concentrations across Australia

Australia is a highly developed country with low population density. Capital cities are situated mainly around the coastline and are subjected to different meteorological conditions. This complex set of drivers is expected to result in varying trends in particulate matter (PM) mass concentrations in urban ambient air across the country. Thus, the aim of this study was to determine the long-term trends in PM₁₀ and PM_2.5 concentrations in capital cities, and to analyse the factors that influenced such trends. The spatial variability of PM concentrations within the capital cities was first established to identify representative stations. Then trends were determined using the Mann-Kendall trend test, Sen's slope, and the generalised additive model. The results show that, in general, the PM concentrations in Australian cities are relatively low (12.1-21.7 μg m^-3 mean daily PM₁₀ and 4.6-8.7 μg m^-3 mean daily PM_2.5) and within the WHO daily limit 95% of the time. Over the past two decades, very small declines of 8.0 × 10^-5-1.1 × 10^-3 μg m^-3.yr^-1 for PM₁₀ and 7.7 × 10^-5-2.6 × 10^-3 μg m^-3.yr^-1 for PM_2.5 were observed while some stations exhibited increase in concentration based on available data; more stations showed a significant monotonic decline for PM₁₀ than PM_2.5. This is attributed to the effectiveness of the implemented emission reduction policies particularly for vehicle exhaust and power generation, given the simultaneous increase in the demand for energy and the number of vehicles over the last two decades. Regarding climate, in the coastal cities of Sydney and Brisbane, high rainfall and strong winds aid in maintaining low PM concentrations despite the significant anthropogenic emissions, while higher PM levels in Darwin can be attributed to its tropical savannah climate, which makes it prone to bushfires and necessitates regular prescribed burnings. PM concentrations increase when exceptional events such as bushfires and dust storms are induced by the extreme climate variability. Further reduction of PM concentrations in Australian cities is unlikely, considering the expanding urbanisation and the changing climate.

Analyzing the heat island magnitude and characteristics in one hundred Asian and Australian cities and regions

Urban heat island is the more documented phenomenon of climate change. Information on the magnitude and the characteristics of the canopy layer urban heat island measured in 101 cities and regions of Asia and Australia and collected through 88 scientific articles, are compiled, evaluated and presented. Data are classified in several clusters according to the experimental protocol used and the type of statistical information reported regarding the magnitude of the urban heat island. Results and detailed analysis are given for each defined cluster. Very significant differences on the UHI intensity are found between the clusters and analyzed in detail. The detailed impact of the main weather parameters and conditions on the magnitude of the UHI is also investigated. The specific influence of anthropogenic thermal fluxes as well as of the urban morphological and construction characteristics to UHI is thoroughly examined. The relation between the UHI intensity and the city size is assessed and global relationships of UHI as a function of the urban population are proposed. The seasonal and diurnal variability of the UHI is analyzed and discussed while specific features and conditions like the urban heat island characteristics in coastal cities and the existence of daytime cool islands are explored. Finally, the impact of the selected reference station and its characteristics is considered.