Photoemission of Iodide from Aqueous Aerosol Particle Surfaces

Woods, Ephraim; Konys, Casey A.; Rossi, Sean R.

doi:10.1021/acs.jpca.8b12323

Cited by 9 publications

(16 citation statements)

References 43 publications

(96 reference statements)

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“…26 Recently, we used the photoemission yield of iodide to study the anion's affinity for the water−air interface in a supersaturated aerosol. 27 The results demonstrate preferential detection of interfacial species, consistent with an estimated electron attenuation length in water of 1 to 3 nm 28−32 at the energies of this experiment. Our goal in this paper is to use this methodology to monitor short-lived transient species, such as the triplet states of photosensitizer molecules, and to measure the initial stage kinetics.…”

Section: ■ Introductionsupporting

confidence: 81%

“…Our analysis assumes that the response is linear with concentration, as we have found for low concentrations of photoemitters in previous studies. 27,38 We collect transient lifetime data by monitoring the aerosol electrometer signal as a function of the delay between the excitation and photoemission laser pulses. In a typical experiment, we average the electrometer signal over 30 laser pulses (3 s) for each delay setting.…”

Section: ■ Experimentsmentioning

confidence: 99%

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Lifetime of Triplet Photosensitizers in Aerosol Using Time-Resolved Photoelectric Activity

Woods

Harris

Leiter

et al. 2020

ACS Earth Space Chem.

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Time-resolved photoelectric activity of aerosol (TPEAA) experiments measure the kinetics of photochemically initiated reactions near the surface of aerosol particles. In the demonstration presented here, TPEAA experiments monitor the evolution of excited triplet states, which are key intermediates in the photochemical formation of secondary organic aerosol (SOA). One example is the decay of the triplet excited state of imidazole-2-carboxaldehyde (IC) in aqueous NaCl aerosol particles. The decay of the triplet IC shows two distinct timescales, indicative of two populations of IC in the particles: aqueous and pure IC. The lifetime in the pure-IC phase is less than 20 ns, and the lifetime associated with aqueous IC is limited by reaction with chloride ions (k = 5.6 × 105 M–1 s–1). The results demonstrate how phase separation in aerosol particles can control reaction pathways and kinetics. In another example, TPEAA monitors the decay of the triplet anthraquinone-2-sulfonate (AQ2S) anion in aqueous NaCl aerosol. The AQ2S triplet reacts with water (k′ = 8.7 × 106 s–1) to produce adduct species. In this case, tuning the wavelength of the photoemission laser permits the preferential observation of the triplet or a combination of the AQ2S triplet and the water adduct. These results bridge a gap between aerosol phase measurements, which are normally steady-state and bulk-phase transient absorption measurements, which typically probe homogeneous phases.

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Section: ■ Introductionsupporting

confidence: 81%

Section: ■ Experimentsmentioning

confidence: 99%

Lifetime of Triplet Photosensitizers in Aerosol Using Time-Resolved Photoelectric Activity

Woods

Harris

Leiter

et al. 2020

ACS Earth Space Chem.

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“…3−7 For example, studies on the photoemission of iodide from aqueous surfaces showed that ionic surfactants attract oppositely charged ions from the bulk to the air−water interface, thereby enhancing the reaction while pushing equally charged ions into the bulk liquid. 7 It has been suggested that electrostatic interactions are key to understanding reactions at interfaces covered by ionic surfactants. An experimental study has shown that the presence of octanoic acid on the surface of an aqueous solution decreases the rate of heterogeneous ozonation of pyrene, whereas the presence of octan-1-ol accelerates it.…”

Section: ■ Introductionmentioning

confidence: 99%

Acid-Catalyzed Oligomerization at the Air–Water Interface Modified by Competitive Adsorption of Surfactants

2019

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Amphiphilic organic compounds that accumulate naturally on the outermost layers of aqueous aerosols totally change the mechanisms involved in the uptake and reactions of volatile organic compounds adsorbed on the surfaces. By means of mass spectrometry of aqueous microjets, we examined how quaternary alkylammonium cations Me(CH 2 ) n−1 N + Me 3 (n = 1, 4, 8, 10, 12, and 14) and nonionic octan-1-ol influence acid-catalyzed oligomerization of gaseous isoprene (ISO) at the air−water interface. The oligomerization is initiated by proton-transfer (PT) reaction from an interfacial hydronium ion to isoprene to form a (ISO)H + and is subsequently followed by chainpropagation (CP) reaction to form (ISO) m≥2 H + . We found that although the total mass spectral signals of (ISO) m H + products were suppressed by the presence of either the alkylammonium cations or octan-1-ol, the suppression by the former surfactants was much larger than that of the latter. The suppression was observed even at aqueous microjets of 5 μM equimolar solution of the alkylammonium cations at which the air−water interface is only sparsely occupied by the alkylammonium cations. We propose that electrostatic repulsions between the alkylammonium cation and the interfacial H 3 O + cause the hindrance of the PT reaction. In contrast, the subsequent CP reactions were not suppressed by the presence of either the alkylammonium cations or octan-1-ol. We suggest that the presence of long-chain organic surfactants hinders the initial PT reaction but hardly suppresses the subsequent CP reaction. Our study has revealed hitherto unrecognized interface-specific roles of surfactants that affect multiphase chemistry in the atmosphere.

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“…41 Several experiments have used ultraviolet photoelectron spectroscopy (UPS) to study the electronic structure of free nanoparticles. [42][43][44][45][46][47][48][49][50][51][52][53] Many of these 107 studies have used a velocity map imaging spectrometer to image a projection the nascent 108 photoelectron distribution of low energy electrons that originated from valence energy 109 5 levels. 42,43,[46][47][48][49][50][51][52][53] Additionally, X-ray photoelectron spectroscopy (XPS) studies have probed free nanoparticles to provide elemental information of the surface.…”

mentioning

confidence: 99%

Using Nanoparticle X-ray Spectroscopy to Probe the Formation of Reactive Chemical Gradients in Diffusion-Limited Aerosols

Jacobs

Kostko

et al. 2019

J. Phys. Chem. A

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For aerosol particles that exist in highly viscous, diffusion-limited states, steep chemical gradients are expected to form during photochemical aging in the atmosphere. Under these conditions species at the aerosol surface are more rapidly transformed than molecules residing in the particle interior. To examine the formation and evolution of chemical gradients at aerosol interfaces, the heterogeneous reaction of hydroxyl radicals (OH) on ~200-nm particles of pure squalane (a branched, liquid hydrocarbon) and octacosane (a linear, solid hydrocarbon), and binary mixtures 21 of the two are used to understand how diffusion limitations and phase separation impact particle 22 reactivity. Aerosol mass spectrometry is used to measure the effective heterogeneous OH uptake 23 coefficient (γeff) and oxidation kinetics in the bulk, which are compared with the elemental composition of the surface obtained using X-ray photoemission. When diffusion rates are fast 25 relative to the reaction frequency, as is the case for squalane and low viscosity squalane-octacosane mixtures, the reaction is efficient (γeff ~ 0.3) and only limited by the arrival of OH to the interface. However, for cases where the diffusion rates are slower than reaction rates, as in pure octacosane and higher viscosity squalane-octacosane mixtures, the heterogeneous reaction occurs in a mixinglimited regime and is ~10x slower (γeff ~ 0.03). This is in contrast to carbon and oxygen K edge Xray absorption measurements that show that the octacosane interface is oxidized much more rapidly than that of pure squalane particles. The O:C ratio of the surface (estimated to be the top 6-8 nm of the interface) is measured to change with a rate constant of (3.0±0.9)x10-13 and (8.6±1.2)x10-13 cm 3 molecule-1 s-1 for squalane and octacosane particles, respectively. The differences in surface oxidation rates are analyzed using a previously published reaction diffusion model, which suggests that a 1-2 nm highly oxidized crust forms on octacosane particles, whereas in pure squalane the reaction products are homogenously mixed within the aerosol. This work 37 illustrates how diffusion limitations can form particles with highly oxidized surfaces even at 38 relatively low oxidant exposures, which is in turn expected to influence their microphysics in the 39 atmosphere. 40

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Photoemission of Iodide from Aqueous Aerosol Particle Surfaces

Cited by 9 publications

References 43 publications

Lifetime of Triplet Photosensitizers in Aerosol Using Time-Resolved Photoelectric Activity

Lifetime of Triplet Photosensitizers in Aerosol Using Time-Resolved Photoelectric Activity

Acid-Catalyzed Oligomerization at the Air–Water Interface Modified by Competitive Adsorption of Surfactants

Using Nanoparticle X-ray Spectroscopy to Probe the Formation of Reactive Chemical Gradients in Diffusion-Limited Aerosols

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