| Περίληψη: | Atmospheric aerosols, also known as atmospheric particles, are suspended particles (solid or liquid) in the air with diameters ranging from 1 nm to about 100 μm. Atmospheric aerosols affect the Earth's radiant budget and hence the global climate through its so-called direct and indirect radioactive effects, and also have a negative impact on human health. They can be classified as primary (emitted directly into the particle phase) or secondary (formed in the atmosphere through a series of chemical reactions). Typically, atmospheric particles consist of a mixture of inorganic and organic chemicals, including nitrates, sulfates, ammonia, organic compounds, elemental carbon, sea salt, crystalline compounds and water. The organic aerosol represents a significant fraction of the mass of atmospheric particles, but its sources and chemical composition have not yet been elucidated.
Real-time high resolution aerosol mass spectroscopy was the central measurement technique used in this work. The Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) can continuously measure the chemical composition and size distribution of non-refractory submicron aerosol (NR-PM1). The high-resolution mass spectra provided by the instrument every few minutes contain information about both the organic aerosol sources and processes.
This thesis presents the first HR-ToF-AMS measurements in two major Greek cities (Athens and Patras) and a remote site (Finokalia, Crete) and quantifies the contributions of the various sources to the corresponding organic aerosol levels. In addition, the formation of secondary organic aerosol during the photo-oxidation of m- and p-xylene, two important atmospheric aromatic hydrocarbons, is investigated in the laboratory using an atmospheric simulation chamber.
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