Reactive uptake of ozone by proxies for organic aerosols: Surface versus bulk processes

Abstract

Abstract. Uptake measurements of ozone were conducted with two types of proxies for atmospheric organic aerosols: organic liquids and self-assembled organic monolayers. Alkanes and terminal alkenes were used. The monolayer surface was characterized, prior to and after reaction, using IR spectroscopy. Uptake experiments were conducted using a flow tube reactor coupled to a chemical ionization mass spectrometer. The reactive uptake coefficient, ¾, is shown to be due to reaction with the double bond. For the monolayers, ¾ is composed solely of a surface reactive component and is smaller by at least an order of magnitude than values obtained for a liquid of the same chain length. Uptake by the liquids is higher due to solubility and reaction in the bulk. The phase of the atmospheric organic aerosol will determine the appropriate use of a bulk or surface uptake probability in atmospheric models. Since the aerosol surface is processed and sites are consumed, ¾ is time variant. We define a parameter ¾' as the surface uptake probability per reactive site and determine its value as 9 x 10 -•9 cm: molecule '•. This enables the modeling of surface reactions as surface site concentrations diminish following interaction with the gaseous species.

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

“…49,53,54 However, our measured reactive uptake coefficient was a factor of 10 lower than the measurements made on TASAMs by Moise and Rudich. 49 One explanation for this difference may be that the oleate double bond lies in the center of the molecule and is therefore likely to be less accessible than in the TASAMs. Furthermore, the aqueous nature of our surface and high partial pressures of water may further inhibit the reaction.…”

“…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. 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.…”

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations

“…An enhanced reaction probability for the surface reaction is consistent with the fact that the terminal double bond should be the part of the SAM that OH first encounters in the structured monolayer, as also proposed for the NO 3 reaction, 57 and with previous studies showing enhanced reactivity at interfaces compared to the gas phase. [19][20][21][22][23][24][25][26][27][28] Reaction on every collision has also been observed for the reaction of Cl atoms with a C3Q SAM. 22 Although there are a number of studies of the OH oxidation of organics on surfaces and in or on particles, there are 25 measured g = 0.29 for the same surface, indicating that even for saturated alkyl chains, the surface reaction is fast.…”

UV Photodissociation Spectroscopy of Oxidized Undecylenic Acid Films

“…39,41,42,71 It is likely that the initial splitting of POZ occurs with nearly equal probability for the formaldehyde and sebaldehydic acid channels. Indeed, (II) and (VIII) are generated in comparable amounts in the oxidized film.…”

“…21,[60][61][62] Oxidation of unsaturated fatty acids by ozone has been studied by many researchers. 40,42,44,[63][64][65][66][67][68] Related reactions of ozone with ordered Langmuir films of phospholipids on water 45,46,69 or with unsaturated SAM (self-assembled monolayers) 39,41,[70][71][72][73] have also been examined. As a result, both the gas-phase and surface products of ozonolysis of unsaturated fatty acids are relatively well understood.…”