Characterisation and speciation of particulate matter deposited on PTFE and quartz filters

Respirable fractions of airborne ambient particulate matter have been identified over the years as potential health hazards. Due to chemical complexity, extremely small particle sizes, small sample size collected on filters, analysis of such samples is quite problematic. The technique that has a great potential for elemental speciation of fine PM inside the bulk of the filter is a synchrotron-based XAFS spectroscopy. This technique allows to identify the form of an occurrence of an element in the complex mixture, complementing compositional elemental data obtained by X-ray fluorescence and PIXE. Additionally, XAFS is non-destructive and sensitive to ppm concentration levels of many elements when the signals are detected in fluorescence mode. However, it is well known that chemical composition of airborne PM on the surface differs from that of the core. Moreover, many studies have shown that there is a good correlation between the surface composition of aerosol particles and their role in environmental processes, such as atmospheric scavenging and cloud condensation nuclei. Therefore, an XPS was employed to investigate the surface composition of PM. XPS is a non-destructive technique that requires minimum sample preparation. Furthermore, XANES K-edge spectra simulations using FDMNES code were performed in order to simulate lacking reference data. We went even further and performed FDMNES calculations for intermediate energy of sulphur K-edge. Previously such XAS simulations were done in solitary cases, therefore our interest was justified. Following the pre-edge and XANES analyses outcomes of the three investigated filters, and by considering the relative abundance of the metals in them, an EXAFS analysis at the Fe K-edge only was performed. It provided quantitative data of the selected metal core bonding, was performed. In particular the local atomic environment of the Fe site has been revealed, providing bond length referring mostly to the first coordination shell.