Source assessment of fine carbonaceous aerosols in urban Sydney
thesisposted on 2022-03-28, 16:32 authored by Chuanping Meng
Australia is a world famous livable country, with major large Australian cities such as Sydney, Melbourne, Perth and Adelaide all featuring in the top 10 World’s most livable cities in recent years. Sydney, because of its benign environment and mild climate, attracts thousands of tourists and immigrants every year. Although in most of cases Sydney has above average air quality, occasional bush fires/prescribed burns and domestic heating during cold periods can still bring deleterious impacts on air quality and potentially then on human health. Moreover, in summer stronger solar radiation in Sydney is also one of the factors for an increase in PM2.5 levels. Source apportionment research on carbonaceous aerosols, the most substantial component of PM2.5, is still very limited in Sydney. This thesis mainly contains three parts. Chapter 2 and Chapter 3 focus on chemical characterization of non-polar (PAHs and n-alkanes) and typical polar molecular organic tracers in cold period PM2.5 aerosols at an urban Sydney site. Chapter 4 comprehensively assesses the various contributions of fossil/non-fossil and primary/secondary sources to PM2.5 using radiocarbon analyses under different cases. A refined EC tracer method was used to estimate the secondary organic carbon by estimating hourly primary OC/EC ratio ((OC/EC)pri). The findings in Chapter 2 and Chapter 3 indicate that during urban Sydney cold seasons biomass burning, traffic, biogenic activities, secondary sources were distinguished and identified via source indices analysis. Specially, for non-polar organic compounds, 3-4 ring PAHs were mainly from vehicular emissions and 5-6 ring PAHs were derived from biomass burning, while, fossil fuel combustion, notably traffic exhaust made a distinct contribution to n-alkanes concentrations, particularly in winter. Three distinct sources of n-alkanes were identified, and their contributions were estimated using a PCA-MLR model; these sources were, fossil fuel combustion (74%), biomass burning + road dust (20%) and biogenic sources (6%). The chemical analysis of polar organic compounds suggests that the site was significantly influenced by the emissions from wintertime domestic wood combustion and autumn time controlled bushfire prevention burns. In autumn, hardwood was found as a predominant source combined with some softwood burning, whereas in winter hardwood and grass combustion are the main type of biomass burnt. It is apparent that during the cold seasons the primary sources of the polar fraction of the organic component of PM are biomass combustion. For the eight limited selected radiocarbon analysis PM2.5 samples, the average abundances of SOA and PCA were 2.3 μg·m-3 and 8.9 μg·m-3, respectively for the Rozelle and Macquarie University (MQ) sites, accounting for 11% and 42% of the PM2.5 mass. Higher proportions of POCnf (POCnf: non-fossil sources in primary organic carbon (POC)) and ECbiomass (ECbiomass: biomass burning sources in EC) were determined in winter samples, amounting to 60% and 11% compared with 50% and 4% in the summer samples. This suggests that biofuel combustion mainly wood burning for household heating in the cold season would be a major contributor to total carbon in the collected particulates.