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

M. Fraund; D. J. Bonanno; S. China; D. Q. Pham; D. Veghte; J. Weis; J. Weis; J. Weis; G. Kulkarni; K. Teske; M. K. Gilles; A. Laskin; A. Laskin; R. C. Moffet; R. C. Moffet

doi:10.5194/acp-20-11593-2020

Atmospheric Chemistry and Physics (Oct 2020)

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

M. Fraund,
D. J. Bonanno,
S. China,
D. Q. Pham,
D. Veghte,
J. Weis,
J. Weis,
J. Weis,
G. Kulkarni,
K. Teske,
M. K. Gilles,
A. Laskin,
A. Laskin,
R. C. Moffet,
R. C. Moffet

Affiliations

M. Fraund: Department of Chemistry, University of the Pacific, Stockton, California 95204, USA
D. J. Bonanno: Department of Chemistry, University of the Pacific, Stockton, California 95204, USA
S. China: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, USA
D. Q. Pham: Department of Chemistry, University of the Pacific, Stockton, California 95204, USA
D. Veghte: Center for Electron Microscopy and Analysis, The Ohio State University, Columbus, Ohio 43212, USA
J. Weis: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
J. Weis: Department of Chemistry, University of California, Berkeley, California 94720, USA
J. Weis: current address: Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
G. Kulkarni: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, USA
K. Teske: Atmospheric Radiation Monitoring (Southern Great Plains Climate Research Facility), Billings, Oklahoma 74630, USA
M. K. Gilles: Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
A. Laskin: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, USA
A. Laskin: current address: Chemistry Department, Purdue University, West Lafayette, Indiana 47907, USA
R. C. Moffet: Department of Chemistry, University of the Pacific, Stockton, California 95204, USA
R. C. Moffet: current address: Sonoma Technology, Petaluma, California 94954, USA

DOI: https://doi.org/10.5194/acp-20-11593-2020
Journal volume & issue: Vol. 20
pp. 11593 – 11606

Abstract

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Atmospheric high-viscosity organic particles (HVOPs) were observed in samples of ambient aerosols collected in April and May 2016 in the Southern Great Plains of the United States. These particles were apportioned as either airborne soil organic particles (ASOPs) or tar balls (TBs) from biomass burning based on spetro-microscopic imaging and assessments of meteorological records of smoke and precipitation data. Regardless of their apportionment, the number fractions of HVOPs were positively correlated (R2=0.85) with increased values of absorption Ångström exponent (AAE) measured in situ for ambient aerosol at the site. Extending this correlation to 100 % HVOPs yields an AAE of 2.6, similar to previous literature reports of the class of light-absorbing organic particles known as brown carbon (BrC). One out of the three samples investigated had a significant number of ASOPs, while the other two samples contained TBs. Although there are chemical similarities between ASOPs and TBs, they can be distinguished based on composition inferred from near-edge absorption X-ray fine structure (NEXAFS) spectroscopy. ASOPs were distinguished from TBs based on their average -COOH/C=C and -COOH/COH peak ratios, with ASOPs having lower ratios. NEXAFS spectra of filtered soil organic brine particles nebulized from field samples of standing water deposited after rain were consistent with ASOPs 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 a particle composition different from ASOPs. 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 of soil inorganics dissolved in the bulk volume of soil brine, which 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. In addition, our results show that ASOPs may only be atmospherically relevant during times when suitable emission conditions are met.

Published in Atmospheric Chemistry and Physics

ISSN: 1680-7316 (Print); 1680-7324 (Online)
Publisher: Copernicus Publications
Country of publisher: Germany
LCC subjects: Science: Physics; Science: Chemistry
Website: http://www.atmospheric-chemistry-and-physics.net/

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