Reactive Uptake of Ozone by Oleic Acid Aerosol Particles:  Application of Single-Particle Mass Spectrometry to Heterogeneous Reaction Kinetics

Abstract

The technique of single-particle mass spectrometry has been coupled to a reaction flow tube to measure the uptake coefficient, γ, of ozone (O 3 ) by oleic acid (9-octadecenoic acid) aerosol particles. The reaction was followed by monitoring the decrease of oleic acid in the size-selected particles as a function of O 3 exposure. The reactive uptake coefficient is found to depend on the size of the particle, with γ meas ranging from (7.3 ( 1.5) × 10 -3 to (0.99 ( 0.09) × 10 -3 for particles ranging in radius from 680 nm to 2.45 µm. It is suggested that the decrease in γ meas with increasing particle size results from the reaction being limited by the diffusion of oleic acid within the particle, and based on our measurements we estimate the value of γ to be (5.8-9.8) × 10 -3 for particles that are not limited by oleic acid diffusion. A reaction model that includes simultaneous diffusion and reaction of both O 3 and oleic acid is developed and used to fit the observed rates of reaction. Solutions obtained from this model indicate that oleic acid must diffuse within the particle more slowly than is predicted by the measured oleic acid self-diffusion constant. 1 It is proposed that this oleic acid-diffusionlimited uptake is attributable to the ozonolysis reaction products. Furthermore, these experiments demonstrate that it is not always possible to describe heterogeneous uptake by a model that decouples all relevant processes, including reaction and diffusion. Finally, the possible implications that these findings have for the role of particle morphology in the reaction of gas-phase species with atmospheric aerosols are discussed.

Photoelectron resonance capture ionization mass spectrometry: a soft ionization source for mass spectrometry of particle‐phase organic compounds

“…The major oxidation products measured by PERCI-MS, detected as [M-H] À , are predicted by two reaction pathways during the ozonolysis of oleic acid. As reported in the literature [23][24][25] and illustrated in Scheme 1, ozone adds across the double bond in oleic acid to form a primary ozonide (1), which can decompose by two alternative pathways to produce 1-nonanal (142 Da) (2), and azelaic acid (188 Da) (3) or nonanoic acid (172 Da) (4) and 9-oxononanoic acid (158 Da) (5). Azelaic acid and nonanoic acid are formed by rearrangement of the Criegee intermediates (I) and (II), respectively.…”

“…Recently, other methods of on-line particle mass spectrometry have been applied to the study of oleic acid ozonolysis. 24,25 While successful at measuring total organic aerosol, however, a direct measurement of reaction products was greatly limited by excessive fragmentation of the molecular products during the ionization step. Previous attempts to measure this reaction 24,25 in real time have yielded unreacted oleic acid peaks that made up less than 1% and 15% of the total ion signal.…”

Heterogeneous chemistry and reaction dynamics of the atmospheric oxidants, O3, NO3, and OH, on organic surfaces

“…[62][63][64][65][66] Within the body of literature on O 3 reactions with aerosols, investigations of the ozonolysis of oleic acid aerosols are of particular interest because these particulates appear in relative high abundance in certain regions of the atmosphere. [67][68][69][70] From these studies, reactive uptake coefficients have been determined to be generally on the order of 10…”

The Oxidation of Oleate in Submicron Aqueous Salt Aerosols: Evidence of a Surface Process

“…12,[28][29][30][31][32][33][34][35][36] Several factors have motivated these studies, including: quantifying the time scale for organic aerosol to be converted from hydrophobic to hydrophilic via oxidation thereby influencing their CCN ability, estimating the lifetime of unsaturated organics in aerosol particles, and evaluating organic aerosol oxidation as a potential source of volatile organics. The reaction has been studied using pure oleic acid aerosols, [37][38][39][40][41][42][43][44][45] 2-30 nm thick films on polystyrene beads, 46 ∼1 µm thick films on aqueous sea salt aerosol 47 and on macroscopic films in coated wall flow tube studies. [48][49][50][51][52] Both volatile and involatile products of oleic acid ozonolysis have been identified, including nonanaldehyde, nonanoic acid, 9-oxononanoic acid, and azelaic acid.…”

“…[48][49][50][51][52] Both volatile and involatile products of oleic acid ozonolysis have been identified, including nonanaldehyde, nonanoic acid, 9-oxononanoic acid, and azelaic acid. 38,46,48 It has also been suggested that ozonolysis may lead to polymerization in pure oleic acid particles 41,42 and for other unsaturated organics in self-assembled monolayers 53,54 and thin films. 55 Overall, existing experimental data suggest that the reactive uptake coefficient, γ O 3 , for O 3 on pure oleic acid is on the order of 10 -3 at room temperature.…”