AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
IEPOX-Derived Organosulfates Contribute a Significant Portion of the Aerosol Mass Spectral Tracer Ion of IEPOX-derived SOA and Its Implications
YUE ZHANG, Yuzhi Chen, Manjula Canagaratna, Sri Hapsari Budisulistiorini, Tianqu Cui, Zhenfa Zhang, Avram Gold, John Jayne, Douglas Worsnop, Barbara Turpin, Jason Surratt, Univ. of North Carolina, Chapel Hill/Aerodyne Research, Inc.
Abstract Number: 714 Working Group: Aerosol Chemistry
Abstract Isoprene-derived secondary organic aerosols (SOA), an important fraction of the global aerosol budget, often form through acid-catalyzed heterogeneous reactions of isoprene epoxydiols (IEPOX) onto acidified sulfate particles. An enhanced fraction of the C5H6O+ ion (fC5H6O), with a mass-to-charge (m/z) ratio of 82, is found to be present in aerosol mass spectra of IEPOX-derived SOA from both field and laboratory measurements and commonly identified as a tracer ion. The origin of the tracer ion remains uncertain due to the complex composition of IEPOX-derived SOA.
2-Methyltetrols and 2-methyltetrol organosulfates, the two groups of compounds that account for more than 90% of trans-β-IEPOX derived SOA, were atomized into the Aerodyne Aerosol Chemical Speciation Monitor (ACSM). The mass spectral data show that a large fC5H6O surprisingly appears in the mass spectrum of pure 2-methyltetrol organosulfates aerosols. Positive matrix factorization (PMF) was applied to the time-series data of IEPOX reacting with acidified ammonium sulfate particles in the UNC chamber to examine the time-dependent compositional changes of the SOA. PMF-derived factor was successfully resolved for 2-methyltetrol organosulfates in the aerosol phase, with a correlation factor greater than 0.9 when compared with pure standards and the particle into liquid sampler (PILS) coupled to hydrophilic interaction chromatography interfaced to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS). Multilinear engine (ME-2) was used to source apportion the organosulfate fractions from field data obtained from Atlanta, GA, and Look Rock, TN. Results suggest a higher than expected organosulfate mass fraction present in ambient IEPOX-derived SOA. Our findings indicate that the tracer ion at m/z 82 for IEPOX-derived SOA measured during field and laboratory studies is likely a fragmentation product of organosulfates that are prevalent in ambient IEPOX-derived SOA. Higher organosulfate concentrations may lead to important changes in the aerosol physical properties and chemical reactivity due to their unique properties.