Heterogeneous Ozonolysis of Squalene: Gas-Phase Products Depend on Water Vapor Concentration

Abstract

Previous work examining the condensed-phase products of squalene particle ozonolysis found that an increase in water vapor concentration led to lower concentrations of secondary ozonides, 2 increased concentrations of carbonyls, and smaller particle diameter, suggesting that water changes the fate of the Criegee intermediate. To determine if this volume loss corresponds to an increase in gas-phase products, we measured gas-phase volatile organic compound (VOC) concentrations via proton-transfer-reaction time-of-flight mass spectrometry. Studies were conducted in a flow-tube reactor at atmospherically relevant ozone (O3) exposure levels (5-30 ppb h) with pure squalene particles. An increase in water vapor concentration led to strong enhancement of gas-phase oxidation products at all tested O3 exposures. An increase in water vapor from near zero to 70% relative humidity (RH) at high O3 exposure increased the total mass concentration of gas-phase VOCs by a factor of three. The observed fraction of carbon in the gas-phase correlates with the fraction of particle volume lost. Experiments involving O3 oxidation of shirts soiled with skin oil confirms that the RH dependence of gas-phase reaction product generation occurs similarly on surfaces containing skin oil under realistic conditions. Similar behavior is expected for O3 reactions with other surface-bound organics containing unsaturated carbon bonds.

Ozone Initiates Human-Derived Emission of Nanocluster Aerosols

“…Five groups of four human volunteers were recruited: three young-adult groups (A1-A3; average age 25.1 years, range [19][20][21][22][23][24][25][26][27][28][29][30], one teenager group (T4; average age 13.8 years, range [13][14][15], and one senior group (S5; average age 70.5 years, range 68-72). NCA emissions were investigated for groups A1, A2, T4 and S5.…”

Indoor Surface Chemistry: Developing a Molecular Picture of Reactions on Indoor Interfaces

“…[87][88][89] Most recently, it was shown that adsorbed water can increase the amount of volatile gas-phase products of squalene thin-film oxidation, as well as changing the distribution of squalene oxidation products to yield more aldehyde and ketone products. 90 Squalene films are models for skin and fabrics soiled with skin oil. It was also thought that surface reactions of other adsorbed OCs containing unsaturated carbon bonds will show a similar relative humidity dependence.…”

Catalytic Ozonation of Cinnamaldehyde to Benzaldehyde over Ca(OH)2

“…Process III, the zwitterionic peroxide reacted with the aldehyde to yield the secondary ozonide, was reversible [24] . When water is present in the reaction system, H + attacks zwitterionic peroxide to produce H 2 O 2 , [25] and it continually oxidizes the aldehydes, one of the products in process II‐a and II‐b, to carboxylic acids [26]…”