Research into Aerosols, Films and wider Atmospheric Chemistry.

Organic aerosols in indoor and outdoor air often contain both hydrophilic and
hydrophobic components, but the nature of how these compounds are arranged within
an aerosol droplet remains largely unknown. We have developed a range of novel
experimental approaches to study molecular processes at air–water and air–solid
interfaces as well as in levitated aerosol particles and droplets e.g. demonstrating that
acoustic trapping[1] can be used to levitate and manipulate droplets of soft matter, such
as lyotropic mesophases formed from self-assembly of different surfactants and lipids,
which can be analysed in a contact-less manner by X-ray scattering in a controlled
gas-phase environment. We have shown[2,3,4,5,6] that fatty acids in proxies for
atmospheric aerosols from cooking and sea spray self-assemble into highly ordered
three-dimensional nanostructures that may have implications for environmentally
important processes in indoor and outdoor air. We investigated the atmospheric
lifetimes of major components of cooking emissions with unique surfactant properties
that may enable them to survive in the urban atmosphere for an extended period in
self-assembled molecular matrices.[3] We have followed the kinetics of sub-μm selfassembled
films using Small-Angle X-ray Scattering (SAXS) validated by simultaneous
Raman microscopy.[4] Our experiments demonstrated that self-assembled material is
retained even upon extended exposure to high ozone concentrations. In the indoor
space, we have investigated self-assembly of films on solid substrates („window
grime“).[5] Kinetic modelling[6,7] linked to studies of multi-component cooking emission
proxies was used to estimate the potential impact on urban air quality of these
extended lifetimes of reactive species that have previously been assumed to be shortlived
and removed rapidly from the atmosphere. We suggest that lyotropic-phase
formation likely occurs in the atmosphere, with potential implications for residence
times and other aerosol characteristics both in indoor and outdoor air.
References
[1] A. M. Seddon, S. J. Richardson, K. Rastogi, T. S. Plivelic, A. M. Squires, and C. Pfrang, The
Journal of Physical Chemistry Letters 7 (7), 1341-1345 (2016)
[2] Milsom, A., Squires, A. M., Ward, A. D. and Pfrang, C., Accounts of Chemical Research 56,
2555–2568 (2023).
[3] C. Pfrang, K. Rastogi, E. R. Cabrera-Martinez, A. M. Seddon, C. Dicko, A. Labrador, T. S.
Plivelic, N. Cowieson, and A. M. Squires, Nature Communications 8, 1724 (2017).
[4] Milsom, A., Squires, A. M., Terrill, N. J., Ward, A. D. and Pfrang, C., Faraday Discussions
226, 364–381 (2021).
[5] Milsom, A., Squires, A. M., Skoda, M. W. A., Gutfreund, P., Mason, E., Terrill, N. J. and
Pfrang, C., Environmental Science – Atmospheres (Special Issue “Brilliant Light Sources”)
2, 964–977 (2022).
[6] Milsom, A., Squires, A. M., Ward, A. D. and Pfrang, C., Atmospheric Chemistry and Physics
22, 4895–4907 (2022).
[7] Milsom, A., Lees, A., Squires, A. M. and Pfrang, C., Geoscientific Model Development 15,
7139–7151 (2022).