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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.

Understanding secondary organic aerosol (SOA) formation processes is a major challenge for the ambient aerosol science, due to the complexity of chemical matrices and the processes involved. Several analytical techniques have been explored for aerosol organic source apportionment. Proton-nuclear magnetic resonance (H-NMR) spectroscopy is an emerging one, suitable especially for water-soluble organic carbon (WSOC), and that can be used for organic characterization in three different approaches: a) analysis of molecular tracers, b) analysis of functional groups, c) factor analysis with spectral deconvolution. The latter offers a quantitative and simplified description of the thousands of individual species. NMR "factors" extracted by factor analysis typically correspond to a large group of WSOC constituents with similar chemical composition and time trend behaviour that are characteristic of different sources and/or atmospheric processes (Zhang et al. 2011). Two intensive field campaigns were conducted in the Po Valley, Italy, in the cold season during 2013, in February and October, in the framework of the Supersito project funded by Region Emilia-Romagna (http://www.arpa.emr.it/index.asp?idlivello=1459). Samples of fine aerosol particles (PM2.5 and PM1) were collected at an urban site (Bologna, BO) and a rural one (San Pietro Capofiume, SPC). ISAC-CNR in Bologna analysed PM1 by H-NMR spectroscopy, while Ferrara University analysed several polar organic tracers such as primary saccharides, sugar alcohols, anhydrosugars and carboxylic acids by GC/MS in PM2.5 (Pietrogrande et all. 2014). Multivariate factor analysis (positive matrix factorization, PMF) provided four H-NMR factors at both the urban and the rural sites. Dominance of biomass burning is evident at both sites. Specifically, primary organic aerosol from biomass burning (BB-POA) accounted for 30% of WSOC in BO, and 40% in SPC. Two biomass burning secondary organic aerosol factors (BB-SOA) represented 60% of WSOC in BO and are 50% in SPC. Only 10% of WSOC could be attributed to sources other than biomass burning, at both sites. The correlations between PMF H-NMR factors and the polar organic tracers measured by GC/MS were also evaluated. The molecular tracers included anhydrosugars, which are known biomass burning tracers, and carboxylic acids, which can be formed by traffic exhaust, photo oxidation of unsaturated carboxylic acids, oxidation of polyciclic aromatic hydrocarbons or phtalates, products of secondary photo-oxidation reactions, wood combustion. The results indicate that the anhydrosugars (levoglucosan and its isomers, galactosan and mannosan) showed good correlations with BB-POA factor at both sites. Glycolic, malic, phtalic, pimelic, 2-cheto glutaric, succinic, glutaric, adipic, azelaic acids, erythritol and arabinose showed instead high correlations with the BB-SOA factors. In conclusion, the comparison of datasets from distinct analytical methodology proved to be particularly useful to constrain the source apportionment of the polar fraction of organic particulate matter

This work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Centre (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulphate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artefacts in individual instruments, such as the overestimation of m/z 44 from organic aerosol. This effect was quantified by the m/z (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 up to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artefact was applied to the measurements acquired during this study. For some instruments (those with high artefacts), this fragmentation table adjustment led to an “overcorrection” of the f44 (m/z 44/Org) signal. This correction based on measurements made with pure NH4NO3, assumes that the magnitude of the artefact is independent of chemical composition. Using data acquired at different NH4NO3 mixing ratios (from solutions of NH4NO3 and (NH4)2SO4) we observe that the magnitude of the artefact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO3 mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artefact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry.

This work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Center (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulfate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artifacts in individual instruments, such as the overestimation of m/z 44 from organic aerosol. This effect was quantified by the m/z (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artifact was applied to the measurements acquired during this study. For some instruments (those with high artifacts), this fragmentation table adjustment led to an “overcorrection” of the f44 (m/z 44/Org) signal. This correction based on measurements made with pure NH4NO3, assumes that the magnitude of the artifact is independent of chemical composition. Using data acquired at different NH4NO3 mixing ratios (from solutions of NH4NO3 and (NH4)2SO4) we observe that the magnitude of the artifact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO3 mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artifact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry.