Atmospheric reaction chemistry of cloud droplets and aerosol by laser tweezers and neutron scattering

Research output: ThesisDoctoral Thesis

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Aerosols and their indirect contribution to the Earth’s climate remains a poorly understood field. The indirect effect of aerosols on the climate refers to aerosol ability to form cloud condensation nuclei (CCN) and affect cloud properties. Naturally forming, thin organic films exist on the surface of atmospheric aerosols and have the ability to influence aerosol behaviour. Given the oxidative nature of the atmosphere, thin organic films on the surface of aerosols are readily oxidised which will impact on CCN formation and the properties of cloud droplets, affecting the Earth’s climate indirectly.The purpose of this thesis was to investigate the oxidation of atmospherically relevant thin films at the air water interface using the complementary techniques of optical trapping and neutron and X-ray reflectometry, to determine whether such reactions are important in the atmosphere. An optical trapping technique was developed to coat individual solid silica beads with a thin film of oleic acid and characterise both the size and wavelength dependent refractive index of the core silica aerosol and the oleic acid coating using white light Mie scattering. The size of the core aerosol and coating thickness were determined to a precision of ± 0.5 nm and 1 nm respectively. The oxidation of monolayer organic films of atmospheric proxies at the air-water interface was studied using neutron reflectometry and the common atmospheric oxidants, O3, •OH, NO3•, SO4•−. These studies provided insight into the oxidation mechanism of the film as well as film persistence and thickness. Furthermore, the oxidation of monolayer films was also found to be independent of the viscosity and ionic strength of the solution that the film was present on. X-ray reflectivity studies were carried out on the oxidation of monolayer organic films extracted from real atmospheric aerosol and sea-water samples at the air-water interface. The films were found to be inert to gaseous ozone indicating a lack of unsaturated material in atmospheric samples and that oxidation by gaseous ozone may not be important in the atmosphere.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • King, Martin, Supervisor
  • Ward, Andrew D., Supervisor, External person
  • Waltham, Dave, Advisor
Thesis sponsors
Award date1 Feb 2016
Publication statusUnpublished - 2016


  • Aerosol
  • Thin film
  • Monolayer
  • Oxidation
  • Optical Tweezers
  • Neutron Reflectivity
  • X-Ray Reflectivity

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