Experimental observation of 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, Christian Pfrang

Research output: Contribution to journalArticlepeer-review

Abstract

Atmospheric aerosol hygroscopicity and reactivity play key roles in determining an 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, thus addressing a current gap in knowledge 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 well-being.

Original languageEnglish
Pages (from-to)13571-13586
Number of pages16
JournalAtmospheric Chemistry and Physics
Volume24
Issue number23
Early online date10 Dec 2024
DOIs
Publication statusPublished - 10 Dec 2024

Data Availability Statement

Data supporting this study are available in the Supplement and from the corresponding author upon request.

Acknowledgements

This work was carried out with the support of the Diamond Light Source (DLS), instrument I22 (proposal SM21663). Adam Milsom wishes to acknowledge funding from NERC SCENARIO DTP and CENTA DTP. The work was supported by NERC. The authors would like to thank Nick Terrill (DLS), Tim Snow (DLS) and Lee Davidson (DLS) for technical support during beamtime experiments; Jacob Boswell is acknowledged for help at beamtimes. The authors are grateful to the Central Laser Facility for access to key equipment for the Raman work simultaneously with the DLS beamtime experiments.

Funding

This research has been supported by the Natural Environment Research Council (NERC) through grant nos. NE/T00732X/1, NE/L002566/1 and NE/L002493/1.

ASJC Scopus subject areas

  • Atmospheric Science

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