Preprints
https://doi.org/10.5194/amt-2020-398
https://doi.org/10.5194/amt-2020-398

  02 Nov 2020

02 Nov 2020

Review status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Investigation of structural changes of atmospheric aerosol samples during two thermal-optical measurement procedures (EUSAAR2, NIOSH870)

Theresa Haller1, Eva Sommer1, Thomas Steinkogler3, Christian Rentenberger1, Anna Wonaschuetz1, Anne Kasper-Giebl3, Hinrich Grothe2, and Regina Hitzenberger1 Theresa Haller et al.
  • 1University of Vienna, Faculty of Physics, Vienna, 1090, Austria
  • 2TU Wien, Institute of Materials Chemistry, Vienna, 1060, Austria
  • 3TU Wien, Institute of Chemical Technologies and Analytics, Vienna, 1060, Austria

Abstract. Thermal-optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal-optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal-optical measurements was found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard soot (CAST). Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low WSOCs loadings. To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e. changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. For all samples, ion chromatography, integrating sphere measurements (yielding black and brown carbon data) and thermal-optical analyses were performed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Therefore we suggest that the widely used term charring should be used carefully when the darkening of a sample during thermal-optical measurement procedures is interpreted.

Theresa Haller et al.

 
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Status: closed
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Theresa Haller et al.

Theresa Haller et al.

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Short summary
Structural changes of carbonaceous aerosol samples during thermal optical measurement techniques cause a darkening of the sample during the heating procedure which can influence the attribution of the carbonaceous material to organic and elemental carbon. We analyzed structural changes of atmospheric aerosol samples occurring during the EUSAAR2 and NIOSH870 measurement protocols with Raman spectroscopy. We found that the darkening of the sample is not necessarily caused by graphitization.