Assessment of X-ray photoelectron spectroscopy for analysis of particulate pollutants in urban air

Abstract

XPS was used to determine hourly and seasonal changes in urban airborne airborne particulates collected in London, UK. Particles were collected on a Burkard spore trap and on PTFE filters for hourly and daily readings, respectively, at periods during the summer and winter. Analysis within 24 h of collection was advisable to avoid build-up of surface contamination from the atmosphere. Carbon and oxygen species dominated the particulate surface with traces of Na+, Mg2+, Ca2+, SiO2, Cl-, NH4+, NO3- and SO4(2-) present. Major species could not be identified on particles collected by the Burkard spore trap as the peaks from the particles coincided with peaks from the tape in the O 1s and C 1s regions. In addition, particle loads were insufficient to establish changes in surface chemistry of the remaining trace species on an hourly basis. Carbon species could be identified for particles collected on PTFE filters as the binding energies for particles and PTFE are separated by 8 eV in the C 1s region. Three regions were identified, namely C-H/C-C, C-O/C-N and C=O/COO-. There was evidence of higher levels of soot during the winter due to more anthropogenic activity, which is in agreement with other data. Fe was a major element detected by electron probe microanalysis in the bulk of winter particles but not on the surface, implying an organic coating on the particles sufficiently thick (> 2 nm) to absorb the Fe photoelectrons.

Characterization of Exhaust Particulates from a Dual Fuel Engine by TGA, XPS, and Raman Techniques

“…Quantitatively the amount of this carbon-oxygen functional group in dual fuel PM structure is found to be lower than that of diesel (high) PM that is in agreement with the assigned carbon-oxygen functional groups for C1s spectra. The presence of similar carbon-oxygen functional groups in diesel exhaust particles and for urban aerosols and activated carbon particulates is reported (Biniak et al 1997;Albers et al 2000;Hutton and Williams 2000;Müller et al 2006). The component peaks for O1s thus complement the findings of similar carbon-oxygen functional groups that have been observed in the carbon spectra.…”

“…Similar observations have been noted previously for diesel exhaust particulates or urban aerosols, and for activated carbon (Biniak et al 1997;Albers et al 2000;Hutton and Williams 2000;Collura et al 2005;Müller et al 2006). When comparing between diesel (high) and dual fuel PM samples, the peak is broadened in the latter case (FWHM = 1.0-1.2 compared to 0.78) indicating a less developed graphitic structure in dual fuel PM as suggested by Müller et al (2006).…”

“…For this reason, the other elements of the blank filter were not detected for this case and lower elemental signals were observed in the XPS spectra than those obtained for the blank filter. These elements have previously been observed in XPS analysis on vehicle exhaust (Hutton and Williams 2000). A sample was also collected for diesel (high) PM on a silver membrane metallic filter to avoid the interference of filter elements such as carbon with the PM elements in XPS analysis.…”

“…These elements are mainly observed in diesel engine/vehicle exhaust PM and have been analyzed by various researchers (Albers et al 2000;Hutton and Williams 2000;Collura et al 2005;Müller et al 2006). Curve fits are performed for individual elements for each PM sample using Gaussian/Lorentzian (G/L ratio = 0.5) line shapes as mentioned earlier.…”

Surface Chemical Composition of Size-Fractionated Urban Walkway Aerosols Determined by X-Ray Photoelectron Spectroscopy

“…A number of studies have used XPS to analyze particulate matters collected with filters (Hutton and Williams 2000;Zhu et al 2001;Paoletti et al 2003;Song and Peng 2009;Vander Wal et al 2011). XPS analysis provides important information about elemental concentrations and chemical states (Faude and Goschnick 1997;Lei et al 2003;Lau et al 2009;Ng et al 2011).…”