Reactive Uptake and Photo-Fenton Oxidation of Glycolaldehyde in Aerosol Liquid Water

Abstract

The reactive uptake and aqueous oxidation of glycolaldehyde were examined in a photochemical flow reactor using hydrated ammonium sulfate (AS) seed aerosols at RH = 80%. The glycolaldehyde that partitioned into the aerosol liquid water was oxidized via two mechanisms that may produce aqueous OH: hydrogen peroxide photolysis (H2O2 + hν) and the photo-Fenton reaction (Fe (II) + H2O2 + hν). The uptake of 80 (±10) ppb glycolaldehyde produced 2–4 wt % organic aerosol mass in the dark (k H* = (2.09–4.17) × 106 M atm–1), and the presence of an OH source increased the aqueous uptake by a factor of 4. Although the uptake was similar in both OH-aging mechanisms, photo-Fenton significantly increased the degree of oxidation (O/C = 0.9) of the aerosols compared to H2O2 photolysis (O/C = 0.5). Aerosol organics oxidized by photo-Fenton and H2O2 photolysis resemble ambient “aged” and “fresh” OA, respectively, after the equivalent of 2 h atmospheric aging. No uptake or changes in particle composition occurred on dry seed aerosol. This work illustrates that photo-Fenton chemistry efficiently forms highly oxidized organic mass in aerosol liquid water, providing a possible mechanism to bridge the gap between bulk-phase experiments and ambient particles.

Photochemical organonitrate formation in wet aerosols

“…Note that atomized particles were passed through a diffusion dryer (3062-NC, TSI; residence time ∼ 5 s) before introducing them to the chamber to minimize the water content. 200 µM H 2 O 2 , previously used by Nguyen et al (2013) in flow tube studies, was used here since this concentration generates ∼ 10 −14 M, an atmospheric aqueous OH concentration (Arakaki et al, 2013), during the reaction with 1 mM glyoxal, according to the updated full kinetic model Lim and Turpin, 2015) (Fig. S1 in the Supplement; model details are in Sect.…”

Influence of metal-mediated aerosol-phase oxidation on secondary organic aerosol formation from the ozonolysis and OH-oxidation of α-pinene

“…Therefore, the oxidation state of SOA can influence the mass loading of SOA in the atmosphere, and is an important parameter required to evaluate the fate of SOA as a result of atmospheric aging. While the oxidation state of SOA is mainly dependent upon the concentration and type of the oxidant and the aging time, it may be also influenced by other factors such as seed aerosol composition3435.…”

“…For example, iron catalyzes SO 2 oxidation in the atmosphere4748, a pathway that contributes a considerable proportion to the global atmospheric sulfate burden49. In addition, particulate iron has important catalytic effects on reactions through Fenton-like chemistry that produces reactive oxygen species (ROS), including hydroxyl radicals and hydrogen peroxide in aerosols35505152. These ROS may influence SOA formation through reactions with condensed organic mass3553.…”

“…In addition, particulate iron has important catalytic effects on reactions through Fenton-like chemistry that produces reactive oxygen species (ROS), including hydroxyl radicals and hydrogen peroxide in aerosols35505152. These ROS may influence SOA formation through reactions with condensed organic mass3553. Recently, a few studies demonstrated that gaseous compounds could be taken up and oxidized on the aerosol liquid water interfaces5455, and the Fenton chemistry was found to be faster at interfaces than in the bulk56.…”

“…These ROS may influence SOA formation through reactions with condensed organic mass3553. Recently, a few studies demonstrated that gaseous compounds could be taken up and oxidized on the aerosol liquid water interfaces5455, and the Fenton chemistry was found to be faster at interfaces than in the bulk56. Several studies have documented the photo-reduction of Fe(III) to Fe(II) in the presence of organic compounds in clouds and fog465758, and it is likely that such reduction also occurs in dark reactions49.…”