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Chamber-based insights into the factors controlling IEPOX SOA yield, composition, and volatility

 

Authors

Joel Thornton — University of Washington
Emma D'Ambro — University of Washington
Siegfried Schobesberger — University of Eastern Finland
Cassandra Gaston — University of Washington
Felipe Lopez-Hilfiker — University of Washington
Ben Hwan Lee — University of Washington
Jiumeng Liu — Pacific Northwest National Laboratory
Alla ZelenyukImre — Pacific Northwest National Laboratory
David Bell — Paul Scherrer Institute
Chris Cappa — University of California, Davis
Taylor Helgestad — University of California Davis
Ziyue Li — University of California, Davis
Alex B Guenther — University of California - Irvine
Jian Wang — Washington University in St. Louis
Kelley C. Barsanti — University of California Riverside
Matthew Wise — Concordia University
Ryan Caylor — Concordia University
Jason Surratt — University of North Carolina, Chapel Hill
Theran Riedel — University of North Carolina, Chapel Hill
John E Shilling — Pacific Northwest National Laboratory

Category

Secondary organic aerosol

Description

Isoprene has the largest emission rates to the atmosphere of any reactive biogenic hydrocarbon. Its subsequent oxidation has the potential to form significant secondary organic aerosol (SOA) that can be modulated by anthropogenic emissions. However, significant uncertainty remains in representing the isoprene SOA formation efficiency and lifetime. We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to chamber measurements of isoprene-derived epoxydiol (IEPOX) reactive uptake to aqueous acidic particles and associated SOA formation. Similar to recent field observations with the same instrument, we detect two molecular components desorbing from the IEPOX SOA in high abundance: C5H12O4 and C5H10O3. The thermal desorption signal of the former, presumably 2-methyltetrols, exhibits two distinct maxima, suggesting it arises from at least two different SOA components with significantly different effective volatilities. Isothermal evaporation experiments illustrate that the most abundant component giving rise to C5H12O4 is semi-volatile, undergoing nearly complete evaporation within 1 hour, while the second less volatile component remains unperturbed and even increases in abundance. We thus confirm, using controlled laboratory studies, recent analyses of ambient SOA measurements showing that IEPOX SOA is of very low volatility and commonly measured IEPOX SOA tracers, such as 2-methyltetrols and C5-alkene triols, are in fact predominantly artifacts of measurement techniques associated with thermal decomposition and/or hydrolysis. We further show that IEPOX SOA volatility continues to evolve via acidity enhanced accretion chemistry on the hours timescale, likely involving both 2-methyltetrols and organosulfates.