| Περίληψη: | Atmospheric organic aerosols (OA) play a significant impact both on climate change as they affect the Earth’s radiation balance and on human health as they can increase the frequency of respiratory, cardiovascular and allergic diseases. Due to the complex nature of atmospheric organic aerosol, current state-of-the-science cannot speciate the thousands of organic compounds present in these particles. Improved understanding of the chemical and physical evolution of organic compounds in our atmosphere is needed in order to be able to link their sources with their concentrations, reduce their levels in urban areas, and quantify their role in climate change. The available chemical transport models often fail to reproduce accurately the concentration and the degree of oxidation of ambient OA. Volatility is one of the most important physical properties of atmospheric OA as it determines the partitioning of organic compounds between the gas and particulate phases, thus having a large impact on aerosol concentrations. The present thesis aims to provide quantitative estimates of OA volatility through both field measurements and laboratory experiments.This work has provided new measurements of the volatility distribution of OA from biomass burning, transportation, cooking, and also more aged transported particles for the city of Athens during winter. These results confirm the at least partially semivolatile character of most OA sources and can be used for the evaluation of the corresponding chemical transport models that predict the OA volatility distribution and oxidation state. In the second phase of the work, the volatility distribution of aged organic aerosol was measured in Crete during early summer. The most important finding was the wide range of volatilities present even in this remote environment and also that both factors included this wide range of components. Therefore, the use of names like semivolatile and low-volatility OA that has been prevalent during the last decade is problematic. These factors are characterized by their oxygen content in this case and not by their volatility.Finally a new experimental method was developed combining thermodenuder and isothermal dilution measurements to constrain the volatility of OA. Organic aerosol produced by cooking emissions was used in order to test the proposed method. The new method reduced the uncertainty of the more volatile part of the OA distribution and also of the corresponding vaporization enthalpy.
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