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Aerosols are ubiquitous in the atmosphere, and play a key role in several environmental processes at local and global scale affecting visibility, air quality, and the climate system. In the present study, proton nuclear magnetic resonance (H-NMR) spectroscopy and aerosol mass spectrometry implemented by an “aerosol chemical speciation monitor” (ACMS) were employed to investigate the chemical composition of submicrometric aerosol collected during a series of intensive field campaigns and to resolve its composition into source-specific fractions including distinct types of primary and secondary organic aerosols (POA and SOA). During the first study, aerosol samples were collected in the Po Valley, in Bologna (urban site) and San Pietro Capofiume (rural site), during the summer 2012 (PEGASOS project) and fall, winter seasons 2013 (SUPERSITO campaigns). The results show that biomass burning POA and SOA dominate the composition of oxygenated organic aerosols in the Po Valley in the cold season, whereas humic-like substances (HULIS), related to chemically-aged SOA types, are prevalent in the summertime. In the second part of this thesis work, SOA samples were produced in laboratory using a flow tube reactor designed to simulate prolonged photochemical ageing. The samples were analyzed by H-NMR and high-liquid performance chromatography (HPLC) for the characterization of isoprene, α-pinene and naphthalene SOA products. The third part of this work was dedicated to two field campaigns at coastal and marine sites in the central Mediterranean region: the first one in Civitavecchia – the port of Rome, for the AIR-SEA Lab project -, and another one onboard the Amerigo Vespucci vessel during the project Dual Use Vespucci. Results showed that PM1 total concentration resulted only 22% lower over the open sea with respect to ports, but the fossil fuel component of OA (the hydrocarbon fraction) was much more enriched in harbors than in off-shore areas.