The investigation of the dynamics of exhaled respiratory aerosols

Abstract

Exhaled respiratory aerosols can carry infectious pathogens and transmit respiratory diseases. They undergo dynamic changes on exhalation and respond to the surrounding environment. The unique aerosol microenvironment can impact pathogen survival and, thus, can affect the airborne survival of infectious pathogens.
This thesis first explores the emission characteristics of exhaled aerosols from a range of respiratory activities through a human participant study. The aerosol number and mass concentration during breathing, speaking, singing and playing woodwind and brass instrument are presented and compared to previous studies. Specifically, increased loudness while playing instruments is associated with higher number concentration and larger particle sizes. These data can be used to refine existing risk models for indoor airborne transmission associated with various respiratory activities.
It then investigates the thermodynamics and physicochemical properties of model exhaled aerosols from the upper respiratory tract. Possible factors that could affect bioaerosol longevity, including phase change, chemical composition, and aerosol hygroscopicity are reported using a Comparative Kinetics Electrodynamic Balance setup and compared with an aerosol thermodynamic model. These data provide insights into the sustained survival of Mouse within a short levitation time, serving as a model system to simulate the early stage of exhalation.
Novel measurements on the acidity of model respiratory fluid sessile droplet were conducted using Aerosol Optical Tweezers and Raman spectroscopy. This study explored the role of bicarbonate/phosphate buffer, compositional changes, CO2 evaporation kinetics, and pH evolution. The enzyme carbonic anhydrase, acting as a catalyst, led to rapid CO2 evaporation and an increase in droplet pH from neutral to alkaline. This provides evidence that a high pH drives the loss of infectivity of SARS-CoV-2 viruses in the aerosol phase over the long term.
These comprehensive findings significantly contribute to understanding the transmission dynamics of respiratory diseases and can inform strategies for mitigating indoor airborne transmission risks.

Date of Award	1 Oct 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jonathan P Reid (Supervisor)