Material Properties of Atmospheric Aerosol through its Lifecycle

Abstract

Atmospheric aerosols are important in the atmosphere and affect global climate and human health. Aerosols are a large area of uncertainty in the climate system, in part, because there are considerable analytical challenges to understanding the properties of micron and nano sized particles and the processes governing aerosol transformation. This thesis uses a range of spectroscopy, spectrometry and imaging methods and combinations thereof to probe material properties of two types of aerosol, organic aerosol and black carbon. The properties explored include vapour pressure, mass diffusion, and absorbance. Organic aerosol partitioning is dependent on the vapour pressures of its' components. The vapour pressures of organic isomers, as measured with a Knudsen Effusion Mass Spectrometer (KEMS), are reported here. The results indicate a difference of up to seven orders of magnitude between measured and group contribution method predicted values. Using KEMS measured vapour pressures instead of predicted vapour pressures results in a larger fraction of a species in the condensed phase. The predictive methods largely do not account for functional group positioning. With organic aerosol consisting of complex mixtures of potentially hundreds of thousands of organics, understanding multicomponent diffusion is important as it affects aerosol partitioning. Diffusion ordered spectroscopy nuclear magnetic resonance was used for the first time to measure multicomponent diffusion coefficients for organic aerosol. Component solubility, mutual diffusion and self-diffusion in NMR experiments, binary and multicomponent diffusion, and finally models of obstruction were all explored using this technique. Black carbon's effect on climate is largely due to its ability to absorb radiation. Absorption, in carbon materials, is related to sp2 hybridization, or graphitic bonding. Raman spectroscopy and near edge X-ray absorption structure (NEXAFS) spectroscopy were applied to a range of reference standards to understand systematic uncertainties in determining carbon bonding. A chosen method for determining graphitization was then used in combination with transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and scanning tunnelling x-ray microscopy (STXM) to analyse anthropogenic aerosol and African biomass burning samples. Using this combination of methods, the morphology, elemental composition, sp2 hybridization, and carbon to oxygen ratios were found for each particle for a detailed characterization of aerosol mixing state.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Hugh Coe (Supervisor), Gordon Mcfiggans (Supervisor), Carl Percival (Supervisor) & David Topping (Supervisor)