Chemical nature and sources of particulate matter in urban areas
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Particulate matter (PM) air pollution adversely affects human health and can lead to premature deaths. The sources of air pollution, however, remain poorly understood especially in urban areas with intense human activities. This thesis presents source apportionment studies of PM air pollution to improve our knowledge of the most important sources in urban cities regarded as typical of those found in moderately populated developed-world countries (e.g. Ireland) and heavily-polluted megacities in developing-world countries (e.g. China). An advanced nation-wide air quality (AQ) pilot monitoring network was established in Ireland using high-time resolution aerosol chemical speciation monitors. The AQ network is capable of providing real-time information about PM mass concentration and chemical composition. Using the sophisticated fingerprinting techniques associated with the mass spectrometry technology, we can better inform emissions reduction policies and help to ensure the most appropriate air pollution sources are targeted. Dublin experienced frequent particulate air pollution events during winter 2016, with episodic PM1 concentrations exceeding 300 μg m-3. Solid fuel, such as peat and wood, though consumed by <13% of the households, contributed up to 70% of the pollution during these exceedance episodes. Pollution events due to solid fuel burning were also observed in Galway. Thus, emission control of solid fuel burning, especially peat burning, should be targeted to improve the air quality across Ireland in winter. In contrast, in summer, the PM was dominated by secondary organic and inorganic aerosol which was found to originate from the long-range transport. In urban cities in North China, traffic, biomass burning, cooking, and coal combustion were the major pollution sources. In addition, secondary aerosol was found to contribute substantially (up to 55%) to PM in episodic events. In Beijing, traffic-related emissions were dominant during low pollution periods, contributing ~65% of total trace element mass. However, coal combustion-related particulate trace elements dominate (58%) during pollution periods. Therefore, reducing the primary emission and controlling the emission of secondary precursor gases are important to improve the air quality in China.