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Preprints
https://doi.org/10.5194/acp-2020-255
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-255
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  31 Mar 2020

31 Mar 2020

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A revised version of this preprint is currently under review for the journal ACP.

Optical properties and composition of viscous organic particles found in the Southern Great Plains

Matthew Fraund1, Daniel J. Bonanno1, Swarup China2, Don Q. Pham1, Daniel Veghte3, Johannes Weis4,5,a, Gourihar Kulkarni2, Ken Teske6, Mary K. Gilles4, Alexander Laskin2,b, and Ryan C. Moffet1,c Matthew Fraund et al.
  • 1Department of Chemistry, University of the Pacific, Stockton, California, 95204, USA
  • 2Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, USA
  • 3Center for Electron Microscopy and Analysis, The Ohio State University, Columbus, Ohio, 43212, USA
  • 4Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
  • 5Department of Chemistry, University of California, Berkeley, California, 94720, USA
  • 6Atmospheric Radiation Monitoring (Southern Great Plains Climate Research Facility), Billings, Oklahoma, 74630, USA
  • acurrent address: Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
  • bcurrent address: Chemistry Department, Purdue University, West Lafayette, Indiana, 47907, USA
  • ccurrent address: Sonoma Technology, Petaluma, California, 94954, USA

Abstract. Atmospheric high viscosity organic particles (HVOP) were observed in samples of ambient aerosol collected on April and May 2016 in the Southern Great Plains of the United States. These particles were apportioned as either airborne soil organic particles (ASOP) or tar balls (TB) from biomass burning based on spetro-microscopic imaging and assessment of meteorological records of smoke and precipitation data. Regardless of their apportionment, the number fractions of HVOP were positively correlated (R2 = 0.85) with increased values of Ångström absorption exponent (AAE) measured in-situ for ambient aerosol at the site. Extending this correlation to 100 % HVOP yields an AAE of 2.6, similar to previous literature reports of the class of light absorbing organic particles known as brown carbon (BrC). Although there are chemical similarities between ASOP and TB, they can be distinguished based on composition inferred from near edge absorption X-ray fine structure (NEXAFS) spectroscopy. ASOP were distinguished from TB based on their average −COOH/C=C and −COOH/COH peak ratios, with ASOP having lower ratios. NEXAFS spectra of filtered soil organic brine particles nebulized from field samples of standing water deposited after rain were consistent with ASOP when laboratory particles were generated by bubble bursting at the air-organic brine interface. However, particles generated by nebulizing the bulk volume of soil organic brine had particle composition different from ASOP. These observations are consistent with the raindrop generation mechanism responsible for ASOP emissions in the area of study. In contrast, nebulized samples carry with them higher fractions soil inorganics dissolved in the bulk volume of soil brine that are not aerosolized by the raindrop mechanism. Our results support the bubble bursting mechanism of particle generation during rainfall resulting in the ejection of soil organics into the atmosphere.

Matthew Fraund et al.

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SGP HISCALE STXM Images and Spectra Matthew Fraund https://doi.org/10.17605/OSF.IO/G8FPW

Matthew Fraund et al.

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Short summary
High viscosity organic particles (HVOP) in Southern Great Plains (SGP) have been analyzed and two particle types were found. Previously studied tar balls and the recently discovered airborne soil organic particles (ASOP) are both shown to be brown carbon (BrC). These particle types can be identified in bulk by an absorption Ångström exponent approaching 2.6. HVOP types can be differentiated by comparing carbon absorption spectra peak ratios between the carboxylic acid, alcohol, and sp2 peaks.
High viscosity organic particles (HVOP) in Southern Great Plains (SGP) have been analyzed and...
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