Aging induced changes on NEXAFS fingerprints in individual combustion particles

Abstract

Abstract. Soot particles can significantly influence the Earth's climate by absorbing and scattering solar radiation as well as by acting as cloud condensation nuclei. However, despite their environmental (as well as economic and political) importance, the way these properties are affected by atmospheric processing of the combustion exhaust gases is still a subject of discussion. In this work, individual soot particles emitted from two different vehicles, a EURO 2 transporter, a EURO 3 passenger car, and a wood stove were investigated on a single-particle basis. The emitted exhaust, including the particulate and the gas phase, was processed in a smog chamber with artificial solar radiation. Single particle specimens of both unprocessed and aged soot were characterized using near edge X-ray absorption fine structure spectroscopy (NEXAFS) and scanning electron microscopy. Comparison of NEXAFS spectra from the unprocessed particles and those resulting from exhaust photooxidation in the chamber revealed changes in the carbon functional group content. For the wood stove emissions, these changes were minor, related to the relatively mild oxidation conditions. For the EURO 2 transporter emissions, the most apparent change was that of carboxylic carbon from oxidized organic compounds condensing on the primary soot particles. For the EURO 3 car emissions oxidation of primary soot particles upon photochemical aging has likely contributed as well. Overall, Correspondence to: M. Ammann (markus.ammann@psi.ch) the changes in the NEXAFS fingerprints were in qualitative agreement with data from an aerosol mass spectrometer. Furthermore, by taking full advantage of our in situ microreactor concept, we show that the soot particles from all three combustion sources changed their ability to take up water under humid conditions upon photochemical aging of the exhaust. Due to the selectivity and sensitivity of the NEXAFS technique for the water mass, also small amounts of water taken up into the internal voids of agglomerated particles could be detected. Because such small amounts of water uptake do not lead to measurable changes in particle diameter, it may remain beyond the limits of volume growth measurements, especially for larger agglomerated particles.

GraftFast Surface Engineering to Improve MOF Nanoparticles Furtiveness

“…In addition, the oxygen XANES spectra recorded using near edge X‐ray absorption fine structure (NEXAFS) O K‐edge (Figure c) reveal the fine spectroscopic signature of different oxygen corresponding to the specific functional groups of the PEG (C=O(CH=CH 2 ) at 531.1 eV and COC at 535.2 eV) before and after GraftFast . First, the spectra recorded using extreme surface probe clearly show the disappearance of the band at 531.1 eV, assigned to the carbonyl group after GraftFast.…”

Chemical imaging of ambient aerosol particles: Observational constraints on mixing state parameterization

“…The mass absorption coefficients ( μ ) for both inorganic and organic components were calculated using the same method as O'Brien et al [] using an average O/C value of 0.4 [ Setyan et al , ] and assuming that the dominant inorganic component was ammonium sulfate: μ in,320 = 11,460 cm 2 /g, μ in,278 = 15,230 cm 2 /g, μ org,320 = 22,500 cm 2 /g, μ org,278 = 1,100 cm 2 /g [ Henke et al , ]. For soot, an average O/C of 0.3 was assumed [ Hopkins et al , ; Zelenay et al , ] and μ org,320 = 29,556 cm 2 /g, μ org,278 = 3,095 cm 2 /g were used. The known density for ammonium sulfate (1.77 g/cm 3 ) was used for the inorganic.…”

XPS surface chemical characterization of atmospheric particles of different sizes

“…There are several methods and instruments for studying different properties of the surface of airborne particulate matter (PM), ranging from morphology to elemental composition (Braun et al, 2007;Coury and Dillner, 2008;Faude and Goschnick, 1997;Kirchner et al, 2003;Ortner et al, 1998;Osan et al, 2006;Zelenay et al, 2011;Zhu et al, 2001). The use of X-ray Photoelectron Spectroscopy (XPS) for chemical surface analysis of airborne particles is not a routine method in environmental applications.…”