title: Light-absorbing oligomer formation in secondary organic aerosol from reactive uptake of isoprene epoxydiols.
abstract: Secondary organic aerosol (SOA) produced from reactive uptake and multiphase chemistry of isoprene epoxydiols (IEPOX) has been found to contribute substantially (upward of 33%) to the fine organic aerosol mass over the Southeastern U.S. Brown carbon (BrC) in rural areas of this region has been linked to secondary sources in the summer when the influence of biomass burning is low. We demonstrate the formation of light-absorbing (290 < λ < 700 nm) SOA constituents from reactive uptake of trans-β-IEPOX onto preexisting sulfate aerosols as a potential source of secondary BrC. IEPOX-derived BrC generated in controlled chamber experiments under dry, acidic conditions has an average mass absorption coefficient of ∼ 300 cm(2) g(-1). Chemical analyses of SOA constituents using UV-visible spectroscopy and high-resolution mass spectrometry indicate the presence of highly unsaturated oligomeric species with molecular weights separated by mass units of 100 (C5H8O2) and 82 (C5H6O) coincident with the observations of enhanced light absorption, suggesting such oligomers as chromophores, and potentially explaining one source of humic-like substances (HULIS) ubiquitously present in atmospheric aerosol. Similar light-absorbing oligomers were identified in fine aerosol collected in the rural Southeastern U.S., supporting their atmospheric relevance and revealing a previously unrecognized source of oligomers derived from isoprene that contributes to ambient fine aerosol mass.
authors.affiliation: Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Ying-Hsuan
authors.initials: YH
authors.lastname: Lin
authors.forename: Sri Hapsari
authors.initials: SH
authors.lastname: Budisulistiorini
authors.forename: Kevin
authors.initials: K
authors.lastname: Chu
authors.forename: Richard A
authors.initials: RA
authors.lastname: Siejack
authors.forename: Haofei
authors.initials: H
authors.lastname: Zhang
authors.forename: Matthieu
authors.initials: M
authors.lastname: Riva
authors.forename: Zhenfa
authors.initials: Z
authors.lastname: Zhang
authors.forename: Avram
authors.initials: A
authors.lastname: Gold
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Kautzman
authors.forename: Jason D
authors.initials: JD
authors.lastname: Surratt
mesh_terms: D000336:Aerosols / Q000032:analysis / Q000737:chemistry*; D018533:Biomass; D002070:Butadienes / Q000737:chemistry*; D002244:Carbon / Q000032:analysis; D004852:Epoxy Compounds / Q000737:chemistry*; D045782:Hemiterpenes / Q000737:chemistry*; D008027:Light; D013058:Mass Spectrometry / Q000379:methods; D010420:Pentanes / Q000737:chemistry*; D015144:Southeastern United States; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013431:Sulfates / Q000737:chemistry
chemical_list: D000336:Aerosols; D002070:Butadienes; D004852:Epoxy Compounds; D045782:Hemiterpenes; D010420:Pentanes; D013431:Sulfates; C005059:isoprene; D002244:Carbon