Products and Mechanisms of Ozone Reactions with Oleic Acid for Aerosol Particles Having Core−Shell Morphologies

Abstract

Heterogeneous reactions of oleic acid aerosol particles with ozone are studied below 1% relative humidity. The particles have inert polystyrene latex cores (101-nm diameter) coated by oleic acid layers of 2 to 30 nm. The chemical content of the organic layer is monitored with increasing ozone exposure by using an aerosol mass spectrometer. The carbon-normalized percent yields of particle-phase reaction products are 20-35% 9-oxononanoic acid, 1-3% azelaic acid, 1-3% nonanoic acid, and 35-50% other organic molecules (designated as CHO T ). There is approximately 25% evaporation, presumably as 1-nonanal. To explain the formation of CHO T molecules and the low yields of azelaic and nonanoic acids, we suggest a chemical mechanism in which the Criegee biradical precursors to azelaic acid and nonanoic acid are scavenged by oleic acid to form CHO T molecules. These chemical reactions increase the carbon-normalized oxygen content (z/x) of the C x H y O z layer from 0.1 for unreacted oleic acid to 0.25 after high ozone exposure. Under the assumption that oxygen content is a predictor of hygroscopicity, our results suggest an increased cloud condensation nuclei activity of atmospherically aged organic particles that initially have alkene functionalities.

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

“…Our partitioning results for the oleate O 3 oxidation products in mixed aqueous salt particles are in qualitative agreement with those of Hearn and Smith 37 and Katrib et al, 46 who observed that nonanoic acid, 9-oxononanoic acid, and azelaic acid are present in the condensed phase after ozone oxidation of pure . Temperature-programmed desorption study of O3 oxidation product volatility.…”

“…This is consistent with the mechanisms proposed by other investigators that include reaction of oleic acid with the Criegee biradical in pure oleic acid particles. 37,39,43,46 The ozone oxidation products that we are able to observe using CIMS with I -as a reagent ion (nonanoic acid, 9-oxononanoic acid, and azelaic acid) were associated with the particle phase at ambient temperature. A temperature-programmed desorption experiment was performed to investigate the gas-particle partitioning of the ozone oxidation products.…”

“…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.…”

Hydroxyl radical-induced photochemical formation of dicarboxylic acids from unsaturated fatty acid (oleic acid) in aqueous solution

“…The reaction of oleic acid (cis-9-octadecenoic, 9C 18 ) with O 3 , OH and NO 3 has recently emerged as a model system to better understand the photooxidation processes affecting unsaturated fatty acids in atmospheric aerosols [11,12]. Oleic acid is degraded through an oxidative cleavage of its double bond to produce C 9 compounds, i.e., nonanoic (C 9 ), 9-oxononanoic (ωC 9 ) azelaic (C 9di ) acids and 1-nonanal (C 9ald ) [13,14,15,16] as well as nitrated carboxylic acids [12]. Secondary photooxidation reactions could initiate the production of lower molecular weight DCAs such as C 2di -C 8di [9,17,18].…”