Preprints
https://doi.org/10.5194/egusphere-2024-905
https://doi.org/10.5194/egusphere-2024-905
05 Apr 2024
 | 05 Apr 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

The impact of nanostructure on hygroscopicity and reactivity of fatty acid atmospheric aerosol proxies

Adam Milsom, Adam M. Squires, Ben Laurence, Ben Wōden, Andrew J. Smith, Andrew D. Ward, and Christian Pfrang

Abstract. Atmospheric aerosol hygroscopicity and reactivity play key roles in determining the aerosol’s fate and are strongly affected by its composition and physical properties. Fatty acids are surfactants commonly found in organic aerosol emissions. They form a wide range of different nanostructures dependent on water content and mixture composition. In this study we follow nano-structural changes in mixtures frequently found in urban organic aerosol emissions, i.e. oleic acid, sodium oleate and fructose, during humidity change and exposure to the atmospheric oxidant ozone. Addition of fructose altered the nanostructure by inducing molecular arrangements with increased surfactant-water interface curvature. Small-Angle X-ray Scattering (SAXS) was employed for the first time to derive the hygroscopicity of each nanostructure by measuring time- and humidity-resolved changes in nano-structural parameters. We found that hygroscopicity is directly linked to the specific nanostructure and is dependent on the nanostructure geometry. Reaction with ozone revealed a clear nanostructure-reactivity trend, with notable differences between the individual nanostructures investigated. Simultaneous Raman microscopy complementing the SAXS studies revealed the persistence of oleic acid even after extensive oxidation. Our findings demonstrate that self-assembly of fatty acid nanostructures can significantly impact two key atmospheric aerosol processes: water uptake and chemical reactivity, thus directly affecting the atmospheric lifetime of these materials. This could have significant impacts on both urban air quality (e.g. protecting harmful urban emissions from atmospheric degradation and therefore enabling their long-range transport), and climate (e.g. affecting cloud formation), with implications for human health and wellbeing.

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Adam Milsom, Adam M. Squires, Ben Laurence, Ben Wōden, Andrew J. Smith, Andrew D. Ward, and Christian Pfrang

Status: open (until 14 Jun 2024)

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Adam Milsom, Adam M. Squires, Ben Laurence, Ben Wōden, Andrew J. Smith, Andrew D. Ward, and Christian Pfrang
Adam Milsom, Adam M. Squires, Ben Laurence, Ben Wōden, Andrew J. Smith, Andrew D. Ward, and Christian Pfrang

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Short summary
We followed nano-structural changes in mixtures found in urban organic aerosol emissions (oleic acid, sodium oleate & fructose) during humidity change & ozone exposure. We demonstrate that self-assembly of fatty acid nanostructures can impact on water uptake & chemical reactivity affecting atmospheric lifetimes, urban air quality (protecting harmful emissions from degradation and enabling their long-range transport) & climate (affecting cloud formation) with implications for human health.