title: O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry.
abstract: A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches approximately 0.9. The hydrogen-to-carbon (H/C, 1.4--1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, approximately 0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R2 = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/OC trends. The highest O/C and OM/OC (1.0 and 2.5, respectively) are observed for aged ambient oxygenated OA, significantly exceeding values for traditional chamber SOA,while laboratory-produced primary biomass burning OA (BBOA) is similar to ambient BBOA, O/C of 0.3--0.4. Hydrocarbon-like OA (HOA), a surrogate for urban combustion POA, has the lowest O/C (0.06--0.10), similar to vehicle exhaust. An approximation for predicting O/C from unit mass resolution data is also presented.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado at Boulder, 216 UCB, Boulder, Colorado 80309, USA.
authors.forename: Allison C
authors.initials: AC
authors.lastname: Aiken
authors.forename: Peter F
authors.initials: PF
authors.lastname: Decarlo
authors.forename: Jesse H
authors.initials: JH
authors.lastname: Kroll
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Worsnop
authors.forename: J Alex
authors.initials: JA
authors.lastname: Huffman
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Docherty
authors.forename: Ingrid M
authors.initials: IM
authors.lastname: Ulbrich
authors.forename: Claudia
authors.initials: C
authors.lastname: Mohr
authors.forename: Joel R
authors.initials: JR
authors.lastname: Kimmel
authors.forename: Donna
authors.initials: D
authors.lastname: Sueper
authors.forename: Yele
authors.initials: Y
authors.lastname: Sun
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Achim
authors.initials: A
authors.lastname: Trimborn
authors.forename: Megan
authors.initials: M
authors.lastname: Northway
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Ziemann
authors.forename: Manjula R
authors.initials: MR
authors.lastname: Canagaratna
authors.forename: Timothy B
authors.initials: TB
authors.lastname: Onasch
authors.forename: M Rami
authors.initials: MR
authors.lastname: Alfarra
authors.forename: Andre S H
authors.initials: AS
authors.lastname: Prevot
authors.forename: Josef
authors.initials: J
authors.lastname: Dommen
authors.forename: Jonathan
authors.initials: J
authors.lastname: Duplissy
authors.forename: Axel
authors.initials: A
authors.lastname: Metzger
authors.forename: Urs
authors.initials: U
authors.lastname: Baltensperger
authors.forename: Jose L
authors.initials: JL
authors.lastname: Jimenez
mesh_terms: D000336:Aerosols / Q000032:analysis*; D002138:Calibration; D013058:Mass Spectrometry / Q000379:methods*
chemical_list: D000336:Aerosols