SET-UP OF INNOVATIVE EXPERIMENTAL METODOLOGIES FOR THE ATMOSPHERIC AEROSOL CHARACTERISATION AND SOURCE APPORTIONMENT
Creators: name: BERNARDONI, VERA
Publisher: name: Universit� degli Studi di Milano
Year: 2010

description: The PhD work presented in this thesis focuses on the set-up of innovative experimental methodologies for the atmospheric aerosol characterisation and apportionment. Many issues are still open in aerosol science. Among them, the identification and quantification of PM sources and the separation between natural and anthropogenic contributions were explored in this work. To improve the state-of-the-art knowledge on aerosols, it has to be considered that the higher is the time- and size-resolution, the more detailed can be the information obtained; moreover, the identification of suitable source tracers plays a key role for the identification and quantification of aerosol sources. In this PhD thesis, three main experimental and modelling improvements were carried out: 1) set-up of an ED-XRF (Energy Dispersive X-Ray Fluorescence) spectrometer for the analysis of size-segregated samples. During the work, an experimental methodology for this kind of analysis was developed, and the obtained results were validated by an inter-comparison with PIXE technique (Particle Induced X-Ray Emission), usually used for size-segregated samples analysis. The developed ED-XRF set-up allows to obtain size-segregated elemental characterisation using a more widespread, cheap, and easy-to-use technique than PIXE. Moreover, it was used to validate a model developed in joint collaboration with the group of the University of Genoa for elemental size distribution determination (see next paragraph); 2)application of the PMF (Positive Matrix Factorization) receptor model to a 4-hour resolved dataset already available. In this work, PMF resolved seven main sources affecting the Milan urban area (re-suspended dust, construction work, secondary compounds, combustion, traffic, industry). Moreover, the combination of the source temporal trends with size-resolved number concentration gave the size-segregated source apportionment, following an approach developed in the past during a collaboration of the research groups of the Universities of Genoa, Milan, and Florence [Mazzei et al., 2007]. Moreover, in this PhD thesis - in joint collaboration with the group of the University of Genoa ? the apportionment methodology approach was further developed to obtain the elemental size distribution without using multistage impactors. As previously mentioned, the ED-XRF analysis on cascade impactor samples analysis set-up in this work allowed the validation of this new methodology for size-segregated distribution estimation; 3) design, set-up and test of a sample preparation line for 14C measurements on aerosol samples carried out jointly with the LABEC-INFN research group. Literature studies showed 14C as a good tracer for the separation of natural and anthropogenic carbonaceous contributions to PM [Szidat et al., 2006]. In this PhD work, a sample preparation line was designed and realised, matching the constraints for the analysis of the organic and elemental carbon fractions (OC and EC, respectively). It was the most innovative, important, and demanding part of the PhD work (it is noteworthy that only another group in the world measures 14C in both OC and EC fractions). New technical solutions were developed during this PhD work and inserted in the final line, and many tests on fractions separation were carried out. First tests on isolated carbon fractions were performed and a preliminary source apportionment was carried out, evidencing limits and perspectives of the approach.