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

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.