title: Real-Time Studies of Iron Oxalate-Mediated Oxidation of Glycolaldehyde as a Model for Photochemical Aging of Aqueous Tropospheric Aerosols.
abstract: The complexation of iron(III) with oxalic acid in aqueous solution yields a strongly absorbing chromophore that undergoes efficient photodissociation to give iron(II) and the carbon dioxide anion radical. Importantly, iron(III) oxalate complexes absorb near-UV radiation (λ > 350 nm), providing a potentially powerful source of oxidants in aqueous tropospheric chemistry. Although this photochemical system has been studied extensively, the mechanistic details associated with its role in the oxidation of dissolved organic matter within aqueous aerosol remain largely unknown. This study utilizes glycolaldehyde as a model organic species to examine the oxidation pathways and evolution of organic aerosol initiated by the photodissociation of aqueous iron(III) oxalate complexes. Hanging droplets (radius 1 mm) containing iron(III), oxalic acid, glycolaldehyde, and ammonium sulfate (pH ∼3) are exposed to irradiation at 365 nm and sampled at discrete time points utilizing field-induced droplet ionization mass spectrometry (FIDI-MS). Glycolaldehyde is found to undergo rapid oxidation to form glyoxal, glycolic acid, and glyoxylic acid, but the formation of high molecular weight oligomers is not observed. For comparison, particle-phase experiments conducted in a laboratory chamber explore the reactive uptake of gas-phase glycolaldehyde onto aqueous seed aerosol containing iron and oxalic acid. The presence of iron oxalate in seed aerosol is found to inhibit aerosol growth. These results suggest that photodissociation of iron(III) oxalate can lead to the formation of volatile oxidation products in tropospheric aqueous aerosols.
authors.affiliation: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Thomas
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Coggon
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.|Environmental Science and Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Hanna
authors.initials: H
authors.lastname: Lignell
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Schilling
authors.affiliation: Environmental Science and Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Environmental Science and Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Rebecca H
authors.initials: RH
authors.lastname: Schwantes
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.|Environmental Science and Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Flagan
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.|Environmental Science and Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: John H
authors.initials: JH
authors.lastname: Seinfeld
authors.affiliation: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: J L
authors.initials: JL
authors.lastname: Beauchamp
mesh_terms: D000336:Aerosols; D005290:Ferric Compounds; D019815:Oxalic Acid; D010084:Oxidation-Reduction; D013996:Time and Motion Studies
chemical_list: D000336:Aerosols; D005290:Ferric Compounds; D019815:Oxalic Acid