The persistence of a proxy for cooking emissions in megacities: a kinetic study of the ozonolysis of self-assembled films by simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and Raman microscopy

Milsom, Adam; Squires, Adam M.; Woden, Ben; Terrill, Nicholas J.; Ward, Andrew D.; Pfrang, Christian

doi:10.1039/d0fd00088d

Cited by 25 publications

(79 citation statements)

References 86 publications

(123 reference statements)

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“…Data related to this study are available in the Supplement and in an open-access repository (https://doi.org/10. 5281/zenodo.5471408; Milsom et al, 2021b). Raw SAXS-WAXS-Raman data are available from the corresponding author upon request.…”

Section: Discussionmentioning

confidence: 99%

An organic crystalline state in ageing atmospheric aerosol proxies: spatially resolved structural changes in levitated fatty acid particles

et al. 2021

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Abstract. Organic aerosols are key components of the Earth's atmospheric system. The phase state of organic aerosols is known to be a significant factor in determining aerosol reactivity, water uptake and atmospheric lifetime – with wide implications for cloud formation, climate, air quality and human health. Unsaturated fatty acids contribute to urban cooking emissions and sea spray aerosols. These compounds, exemplified by oleic acid and its sodium salt, are surface-active and have been shown to self-assemble into a variety of liquid-crystalline phases upon addition of water. Here we observe a crystalline acid–soap complex in acoustically levitated oleic acid–sodium oleate particles. We developed a synchrotron-based simultaneous small-angle and wide-angle X-ray scattering (SAXS and WAXS)–Raman microscopy system to probe physical and chemical changes in the proxy during exposure to humidity and the atmospheric oxidant ozone. We present a spatially resolved structural picture of a levitated particle during humidification, revealing a phase gradient consisting of a disordered liquid crystalline shell and crystalline core. Ozonolysis is significantly slower in the crystalline phase compared with the liquid phase, and a significant portion (34 ± 8 %) of unreacted material remains after extensive oxidation. We present experimental evidence of inert surface layer formation during ozonolysis, taking advantage of spatially resolved simultaneous SAXS–WAXS experiments. These observations suggest that atmospheric lifetimes of surface-active organic species in aerosols are highly phase-dependent, potentially impacting climate, urban air quality and long-range transport of pollutants such as polycyclic aromatic hydrocarbons (PAHs).

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Section: Discussionmentioning

confidence: 99%

An organic crystalline state in ageing atmospheric aerosol proxies: spatially resolved structural changes in levitated fatty acid particles

et al. 2021

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“…The Raman microscopy and ozonolysis experiment is based on the setup detailed in Milsom et al (Milsom et al, 2021b). A long-working-distance objective lens (0.42 numerical aperture) was used to focus a 532-nm laser on the capillary.…”

Section: Methodsmentioning

confidence: 99%

“…This is a long-standing discrepancy and suggests that some physical process is inhibiting the ageing of such aerosols. For these reasons, oleic acid has been the compound of choice for laboratory studies into aerosol heterogeneous oxidation (Gallimore et al, 2017;King et al, 2020;Milsom et al, 2021bMilsom et al, , 2021aPfrang et al, 2017;Woden et al, 2021;Zahardis and Petrucci, 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Some nanostructures, such as the lamellar phase, have highly anisotropic diffusivities resulting in substantially higher diffusivity parallel to the lamellar bilayer compared to the perpendicular direction (Lindblom and Orädd, 1994). This nanostructure formation has been studied in levitated droplets and in coated quartz capillaries (Pfrang et al, 2017;Seddon et al, 2016), where the self-organisation of this proxy system decreased the reactivity of oleic acid by approximately an order of magnitude (Milsom et al, 2021b).…”

Section: Introductionmentioning

confidence: 99%

“…In the present work, we develop a self-organised phase resolved model description of oleic acid ozonolysis and apply this both to kinetic data of the lamellar phase presented recently by Milsom et al (Milsom et al, 2021b) and also to new liquid phase oleic acid ozonolysis data measured by Raman microscopy. We determine the effect on particle diffusivity of both nanostructure formation and the formation of a later stage reaction product, which congregates in the surface region of the film.…”

Section: Introductionmentioning

confidence: 99%

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The impact of molecular self-organisation on the atmospheric fate of a cooking aerosol proxy

Milsom

Squires

Ward

et al. 2021

Preprint

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Abstract. Atmospheric aerosols influence the climate via cloud droplet nucleation and can facilitate the long-range transport of harmful pollutants. The lifetime of such aerosols can therefore determine their environmental impact. Fatty acids are found in organic aerosol emissions with oleic acid, an unsaturated fatty acid, being a large contributor to cooking emissions. As a surfactant, oleic acid can self-organise into nanostructured lamellar bilayers with its sodium salt, and this self-organisation can influence reaction kinetics. We developed a kinetic multi-layer model-based description of decay data we obtained from laboratory experiments of the ozonolysis of coated films of this self-organised system, demonstrating a decreased diffusivity for both oleic acid and ozone due to lamellar bilayer formation. Diffusivity was further inhibited by a viscous oligomer product forming in the surface layers of the film. Our results indicate that nanostructure formation can increase the reactive half-life of oleic acid by an order of days at typical indoor and outdoor atmospheric ozone concentrations. We are now able to place nanostructure formation in an atmospherically meaningful and quantifiable context. These results have implications for the transport of harmful pollutants and the climate.

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Microanalytical Studies of Multiphase Reactions and Particle Aging

Alpert,

Arroyo,

Ammann

2024

Geophysical Monograph Series

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The persistence of a proxy for cooking emissions in megacities: a kinetic study of the ozonolysis of self-assembled films by simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and Raman microscopy

Abstract: Cooking emissions account for a significant proportion of the organic aerosol emitted into the urban environment and high pollution events have been linked to an increased organic content on urban...

Cited by 25 publications

References 86 publications

An organic crystalline state in ageing atmospheric aerosol proxies: spatially resolved structural changes in levitated fatty acid particles

An organic crystalline state in ageing atmospheric aerosol proxies: spatially resolved structural changes in levitated fatty acid particles

The impact of molecular self-organisation on the atmospheric fate of a cooking aerosol proxy

Microanalytical Studies of Multiphase Reactions and Particle Aging

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