Factors that affect the electrical charge states of dry aerosol

Abstract

Aerosol that is formed either in the airways or from the ocean surface can have significant impacts on climate, the environment, and human health. As the risk of respiratory pandemics and extreme weather escalates due to persistent deforestation and climate change, driven by overconsumption of meat and dairy products and unabated fossil fuel burning, the role of aerosol science becomes crucial in mitigating the consequences. One understudied aspect of physical aerosol science are the factors affecting the electric charge. The electrostatic force on an aerosol affects dynamics, agglomeration, hygroscopicity, and deposition, potentially impacting the viability of pathogens within. The ‘charge state’ indicates excess charges on a particle’s surface and the fraction of particles with each charge state are collectively referred to as the ‘electric charge distribution’. Factors influencing electric charge distribution include particle size, shape, composition, salt concentration, fluid pH, and generation method. One main aim of this study is to quantify their impact on the charge of dried particles. Size and salt concentration were most impactful. Measured charge distributions of synthetic lung fluids and artificial seawater show aerosol size, salt concentrations, and protein presence significantly affect charge distribution. Tyler Johnson’s 2020 method of measuring electric charge distributions classifies aerosols by aerodynamic diameter, followed by electric mobility diameter classification. Another aim of this study is to reduce the measurement time. A refined technique developed in this thesis uses continuous voltage scanning that reduces measurement time by 80 %, allowing the charge distributions of shorter-lived aerosol to be measured with 45-second scans. Another aim is to investigate the charge distribution for non-neutralised aerosols, potentially cutting electrostatic classifier costs and increasing usability in broader contexts. We find that non- neutralised aerosol generated by a Collison and an Atomiser are similar across all salts and solutions tested, which means size distributions may be measured without a neutraliser. The final aim is to test the current theory of droplet collision dynamics against data for droplets ten times smaller than previously measured. We find that the current theories fit the data well.