Exploring the Nanostructures Accessible to an Organic Surfactant Atmospheric Aerosol Proxy

Adam Milsom; Adam M. Squires; Isabel Quant; Nicholas J. Terrill; Steven Huband; Ben Woden; Edna R. Cabrera-Martinez; Christian Pfrang

doi:10.1021/acs.jpca.2c04611

Exploring the Nanostructures Accessible to an Organic Surfactant Atmospheric Aerosol Proxy

Adam Milsom, Adam M. Squires, Isabel Quant, Nicholas J. Terrill, Steven Huband, Ben Woden, Edna R. Cabrera-Martinez, Christian Pfrang

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11 Citations (SciVal)

Abstract

The composition of atmospheric aerosols varies with time, season, location, and environment. This affects key aerosol properties such as hygroscopicity and reactivity, influencing the aerosol's impact on the climate and air quality. The organic fraction of atmospheric aerosol emissions often contains surfactant material, such as fatty acids. These molecules are known to form three-dimensional nanostructures in contact with water. Different nanostructures have marked differences in viscosity and diffusivity that are properties whose understanding is essential when considering an aerosol's atmospheric impact. We have explored a range of nanostructures accessible to the organic surfactant oleic acid (commonly found in cooking emissions), simulating variation that is likely to happen in the atmosphere. This was achieved by changing the amount of water, aqueous phase salinity and by addition of other commonly coemitted compounds: sugars and stearic acid (the saturated analogue of oleic acid). The nanostructure was observed by both synchrotron and laboratory small/wide angle X-ray scattering (SAXS/WAXS) and found to be sensitive to the proxy composition. Additionally, the spacing between repeat units in these nanostructures was water content dependent (i.e., an increase from 41 to 54 Å in inverse hexagonal phase d-spacing when increasing the water content from 30 to 50 wt %), suggesting incorporation of water within the nanostructure. A significant decrease in mixture viscosity was also observed with increasing water content from ∼104 to ∼102 Pa s when increasing the water content from 30 to 60 wt %. Time-resolved SAXS experiments on levitated droplets of this proxy confirm the phase changes observed in bulk phase mixtures and demonstrate that coexistent nanostructures can form in droplets. Aerosol compositional and subsequent nanostructural changes could affect aerosol processes, leading to an impact on the climate and urban air pollution.

Original language	English
Pages (from-to)	7331-7341
Number of pages	11
Journal	Journal of Physical Chemistry A
Volume	126
Issue number	40
Early online date	28 Sept 2022
DOIs	https://doi.org/10.1021/acs.jpca.2c04611
Publication status	Published - 13 Oct 2022

Bibliographical note

Funding Information:
A.M. acknowledges funding by the NERC SCENARIO DTP (NE/L002566/1) and support from the NERC CENTA DTP. This work was carried out with the support of the Diamond Light Source (DLS), instrument I22 (proposals SM28020 and SM15121). We acknowledge the help of Olga Shebanova and Andy Smith (DLS) for carrying out the mail-in experiment at DLS. Andy Ward (Central Laser Facility) is acknowledged for help at experiments at DLS. We acknowledge the Research England funded TALENT: Technician Led Equipment Fund for enabling SAXS measurements on the more complex mixtures.

Funding

A.M. acknowledges funding by the NERC SCENARIO DTP (NE/L002566/1) and support from the NERC CENTA DTP. This work was carried out with the support of the Diamond Light Source (DLS), instrument I22 (proposals SM28020 and SM15121). We acknowledge the help of Olga Shebanova and Andy Smith (DLS) for carrying out the mail-in experiment at DLS. Andy Ward (Central Laser Facility) is acknowledged for help at experiments at DLS. We acknowledge the Research England funded TALENT: Technician Led Equipment Fund for enabling SAXS measurements on the more complex mixtures.

ASJC Scopus subject areas

Physical and Theoretical Chemistry

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1021/acs.jpca.2c04611Licence: CC BY

Cite this

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title = "Exploring the Nanostructures Accessible to an Organic Surfactant Atmospheric Aerosol Proxy",

abstract = "The composition of atmospheric aerosols varies with time, season, location, and environment. This affects key aerosol properties such as hygroscopicity and reactivity, influencing the aerosol's impact on the climate and air quality. The organic fraction of atmospheric aerosol emissions often contains surfactant material, such as fatty acids. These molecules are known to form three-dimensional nanostructures in contact with water. Different nanostructures have marked differences in viscosity and diffusivity that are properties whose understanding is essential when considering an aerosol's atmospheric impact. We have explored a range of nanostructures accessible to the organic surfactant oleic acid (commonly found in cooking emissions), simulating variation that is likely to happen in the atmosphere. This was achieved by changing the amount of water, aqueous phase salinity and by addition of other commonly coemitted compounds: sugars and stearic acid (the saturated analogue of oleic acid). The nanostructure was observed by both synchrotron and laboratory small/wide angle X-ray scattering (SAXS/WAXS) and found to be sensitive to the proxy composition. Additionally, the spacing between repeat units in these nanostructures was water content dependent (i.e., an increase from 41 to 54 {\AA} in inverse hexagonal phase d-spacing when increasing the water content from 30 to 50 wt %), suggesting incorporation of water within the nanostructure. A significant decrease in mixture viscosity was also observed with increasing water content from ∼104 to ∼102 Pa s when increasing the water content from 30 to 60 wt %. Time-resolved SAXS experiments on levitated droplets of this proxy confirm the phase changes observed in bulk phase mixtures and demonstrate that coexistent nanostructures can form in droplets. Aerosol compositional and subsequent nanostructural changes could affect aerosol processes, leading to an impact on the climate and urban air pollution.",

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N2 - The composition of atmospheric aerosols varies with time, season, location, and environment. This affects key aerosol properties such as hygroscopicity and reactivity, influencing the aerosol's impact on the climate and air quality. The organic fraction of atmospheric aerosol emissions often contains surfactant material, such as fatty acids. These molecules are known to form three-dimensional nanostructures in contact with water. Different nanostructures have marked differences in viscosity and diffusivity that are properties whose understanding is essential when considering an aerosol's atmospheric impact. We have explored a range of nanostructures accessible to the organic surfactant oleic acid (commonly found in cooking emissions), simulating variation that is likely to happen in the atmosphere. This was achieved by changing the amount of water, aqueous phase salinity and by addition of other commonly coemitted compounds: sugars and stearic acid (the saturated analogue of oleic acid). The nanostructure was observed by both synchrotron and laboratory small/wide angle X-ray scattering (SAXS/WAXS) and found to be sensitive to the proxy composition. Additionally, the spacing between repeat units in these nanostructures was water content dependent (i.e., an increase from 41 to 54 Å in inverse hexagonal phase d-spacing when increasing the water content from 30 to 50 wt %), suggesting incorporation of water within the nanostructure. A significant decrease in mixture viscosity was also observed with increasing water content from ∼104 to ∼102 Pa s when increasing the water content from 30 to 60 wt %. Time-resolved SAXS experiments on levitated droplets of this proxy confirm the phase changes observed in bulk phase mixtures and demonstrate that coexistent nanostructures can form in droplets. Aerosol compositional and subsequent nanostructural changes could affect aerosol processes, leading to an impact on the climate and urban air pollution.

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Exploring the Nanostructures Accessible to an Organic Surfactant Atmospheric Aerosol Proxy

Abstract

Bibliographical note

Funding

ASJC Scopus subject areas

UN SDGs

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HR-2 Discovery Hybrid Rheometer

Small Angle X-Ray Scattering (SAXS)

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