Bouncier Particles at Night: Biogenic Secondary Organic Aerosol Chemistry and Sulfate Drive Diel Variations in the Aerosol Phase in a Mixed Forest.

Authors:
Jonathan H Slade
Jonathan H Slade
School of Marine and Atmospheric Sciences
Stony Brook | United States
Andrew P Ault
Andrew P Ault
University of California
United States
Jenna C Ditto
Jenna C Ditto
Brown University School of Engineering
Ziying Lei
Ziying Lei
The Third Affiliated Hospital of Sun-Yet-Sen University
Amy L Bondy
Amy L Bondy
University of Michigan
United States

Environ Sci Technol 2019 May 24;53(9):4977-4987. Epub 2019 Apr 24.

Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , United States.

Aerosol phase state is critical for quantifying aerosol effects on climate and air quality. However, significant challenges remain in our ability to predict and quantify phase state during its evolution in the atmosphere. Herein, we demonstrate that aerosol phase (liquid, semisolid, solid) exhibits a diel cycle in a mixed forest environment, oscillating between a viscous, semisolid phase state at night and liquid phase state with phase separation during the day. The viscous nighttime particles existed despite higher relative humidity and were independently confirmed by bounce factor measurements and atomic force microscopy. High-resolution mass spectrometry shows the more viscous phase state at night is impacted by the formation of terpene-derived and higher molecular weight secondary organic aerosol (SOA) and smaller inorganic sulfate mass fractions. Larger daytime particulate sulfate mass fractions, as well as a predominance of lower molecular weight isoprene-derived SOA, lead to the liquid state of the daytime particles and phase separation after greater uptake of liquid water, despite the lower daytime relative humidity. The observed diel cycle of aerosol phase should provoke rethinking of the SOA atmospheric lifecycle, as it suggests diurnal variability in gas-particle partitioning and mixing time scales, which influence aerosol multiphase chemistry, lifetime, and climate impacts.

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Source
http://dx.doi.org/10.1021/acs.est.8b07319DOI Listing
May 2019
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