New Experimental Approaches to Measure Respiratory Aerosol and Droplet Transmission of Disease and Droplet Assisted Ionisation Mass Spectrometry

Abstract

There are few technologies available for both measuring respiratory aerosol and droplet
transmission in the context of airborne transmission of disease, particularly when attempting
to measure larger droplets over 20 µm in diameter.
During the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, urgent
attention was drawn to respiratory aerosol and droplet generation. Respiratory aerosol (< 10
µm diameter) have been previously quantified extensively, but few studies measured larger
droplets (>20 µm diameter), and previous studies were limited by small participant cohort sizes leading to low confidence and large variability in results. A new method to measure respiratory droplet transmission of >20 µm diameter was designed, calibrated and implemented during collaboration projects to measure size distributions and concentrations of respiratory droplets in conjunction with measurements of aerosol size distributions and concentrations. This project identified and compared the associated risks between exhalatory activities like breathing, singing, speaking and exercising. Further, the project investigated interparticipant variability, such as between children and adults, as well as between sex, gender, age and weight. Mitigations of respiratory aerosol and droplet transmission with face-masks were also explored.
Additionally, there are significant challenges when attempting to measure aerosol chemical
composition due to their small mass and complex chemistry. Despite recent developments,
aerosol mass spectrometry techniques are often criticised due to the potential interference of
the ionisation method, such as high voltage or temperature, affecting the observed chemical
composition in their data.
A new, voltage-free, contactless approach to ionisation during aerosol mass spectrometry was designed. Droplet-assisted ionisation mass spectrometry (DAI-MS) was constructed,
developed, and modified to measure aerosol chemical composition, while identifying the role
of relative humidity on the ionisation mechanism and efficiency during DAI-MS, in conjunction with the hygroscopicity and phase. Furthermore, this technique was adopted for
analysis of esterification reaction rate enhancement observed in aerosol droplets.

Date of Award	7 May 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Bryan R Bzdek (Supervisor)