Not all types of secondary organic aerosol mix: two phases observed when mixing different secondary organic aerosol types

F. Mahrt; F. Mahrt; L. Peng; L. Peng; L. Peng; J. Zaks; Y. Huang; Y. Huang; P. E. Ohno; P. E. Ohno; P. E. Ohno; N. R. Smith; F. K. A. Gregson; Y. Qin; Y. Qin; C. L. Faiola; C. L. Faiola; S. T. Martin; S. T. Martin; S. A. Nizkorodov; M. Ammann; A. K. Bertram

doi:10.5194/acp-22-13783-2022

Atmospheric Chemistry and Physics (Nov 2022)

Not all types of secondary organic aerosol mix: two phases observed when mixing different secondary organic aerosol types

F. Mahrt,
F. Mahrt,
L. Peng,
L. Peng,
L. Peng,
J. Zaks,
Y. Huang,
Y. Huang,
P. E. Ohno,
P. E. Ohno,
P. E. Ohno,
N. R. Smith,
F. K. A. Gregson,
Y. Qin,
Y. Qin,
C. L. Faiola,
C. L. Faiola,
S. T. Martin,
S. T. Martin,
S. A. Nizkorodov,
M. Ammann,
A. K. Bertram

Affiliations

F. Mahrt: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T1Z1 Canada
F. Mahrt: Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
L. Peng: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T1Z1 Canada
L. Peng: Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
L. Peng: now at: College of Ecology and Environment, Xinjiang University, Urumqi 830017, China
J. Zaks: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T1Z1 Canada
Y. Huang: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T1Z1 Canada
Y. Huang: now at: Anton Paar Canada Inc., 4920 Place Olivia, H4R 2Z8 Saint Laurent, Canada
P. E. Ohno: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
P. E. Ohno: Center for the Environment, Harvard University, Cambridge, MA 02138, USA
P. E. Ohno: now at: Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36849, USA
N. R. Smith: Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA
F. K. A. Gregson: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T1Z1 Canada
Y. Qin: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
Y. Qin: now at: Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
C. L. Faiola: Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA
C. L. Faiola: Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, CA 92697, USA
S. T. Martin: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
S. T. Martin: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
S. A. Nizkorodov: Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA
M. Ammann: Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
A. K. Bertram: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T1Z1 Canada

DOI: https://doi.org/10.5194/acp-22-13783-2022
Journal volume & issue: Vol. 22
pp. 13783 – 13796

Abstract

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Secondary organic aerosol (SOA) constitutes a large fraction of atmospheric aerosol. To assess its impacts on climate and air pollution, knowledge of the number of phases in internal mixtures of different SOA types is required. Atmospheric models often assume that different SOA types form a single phase when mixed. Here, we present visual observations of the number of phases formed after mixing different anthropogenic and biogenic SOA types. Mixing SOA types generated in environmental chambers with oxygen-to-carbon (O/C) ratios between 0.34 and 1.05, we found 6 out of 15 mixtures of two SOA types to result in two phase particles. We demonstrate that the number of phases depends on the difference in the average O/C ratio between the two SOA types (Δ(O/C)). Using a threshold Δ(O/C) of 0.47, we can predict the phase behavior of over 90 % of our mixtures, with one- and two-phase particles predicted for Δ(O/C)<0.47 and Δ(O/C)≥0.47, respectively. This threshold ΔO/C value provides a simple parameter to predict whether mixtures of fresh and aged SOA form one- or two-phase particles in the atmosphere. In addition, we show that phase-separated SOA particles form when mixtures of volatile organic compounds emitted from real trees are oxidized.

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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