Coexistence of three liquid phases in individual atmospheric aerosol particles

Individual atmospheric particles can contain mixtures of primary organic aerosol (POA), secondary organic aerosol (SOA), and secondary inorganic aerosol (SIA). To predict the role of such complex multicomponent particles in air quality and climate, information on the number and types of phases prese...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 118; no. 16; p. 1
Main Authors Huang, Yuanzhou, Mahrt, Fabian, Xu, Shaun, Shiraiwa, Manabu, Zuend, Andreas, Bertram, Allan K
Format Journal Article
LanguageEnglish
Published United States National Academy of Sciences 20.04.2021
Subjects
Aerosols
Air quality
Atmospheric aerosols
Atmospheric models
Climate effects
Coexistence
Liquid phases
Outdoor air quality
Physical Sciences
Polarity
Relative humidity
Vapor phases
atmospheric chemistry
phase behavior
aerosol particles
climate
air quality
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Summary:Individual atmospheric particles can contain mixtures of primary organic aerosol (POA), secondary organic aerosol (SOA), and secondary inorganic aerosol (SIA). To predict the role of such complex multicomponent particles in air quality and climate, information on the number and types of phases present in the particles is needed. However, the phase behavior of such particles has not been studied in the laboratory, and as a result, remains poorly constrained. Here, we show that POA+SOA+SIA particles can contain three distinct liquid phases: a low-polarity organic-rich phase, a higher-polarity organic-rich phase, and an aqueous inorganic-rich phase. Based on our results, when the elemental oxygen-to-carbon (O:C) ratio of the SOA is less than 0.8, three liquid phases can coexist within the same particle over a wide relative humidity range. In contrast, when the O:C ratio of the SOA is greater than 0.8, three phases will not form. We also demonstrate, using thermodynamic and kinetic modeling, that the presence of three liquid phases in such particles impacts their equilibration timescale with the surrounding gas phase. Three phases will likely also impact their ability to act as nuclei for liquid cloud droplets, the reactivity of these particles, and the mechanism of SOA formation and growth in the atmosphere. These observations provide fundamental information necessary for improved predictions of air quality and aerosol indirect effects on climate.
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Edited by Thomas Peter, Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland, and accepted by Editorial Board Member Akkihebbal R. Ravishankara March 2, 2021 (received for review February 7, 2021)
Author contributions: Y.H., F.M., and A.K.B. designed research; Y.H., S.X., M.S., and A.Z. analyzed data; Y.H., F.M., and A.K.B. wrote the paper; Y.H., F.M., and S.X. performed experiments; M.S. and A.Z. set up the kinetic and thermodynamic models and performed the simulations; and A.K.B. oversaw the project.
1Present address: Anton Paar Canada Inc., Saint Laurent H4R 2Z8, QC, Canada.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2102512118