Identification and Quantification of Trace Aerosol Components

Abstract

The identification and quantification of chemical components of aerosol is important for several applications, including the identification of Chemical Warfare Agents (CWAs). However, unambiguous identification of trace components which may be found in concentrations comparable to or below the background aerosol is challenging. This thesis explores two separate approaches for sampling trace aerosol components: by identifying key fingerprints of the aerosol components of interest to allow them to be identified against the background; and by reducing the background aerosol concentration to a negligible level, ensuring that only the particles to be analysed are sampled.

A novel approach to identify trace aerosol components was developed by using a ~5µm radius probe droplet, levitated via Aerosol Optical Tweezers (AOT), as a picolitre sampling volume. The radius and refractive index of the probe droplet can be tracked in real-time to observe changes in the probe droplet as it accretes aerosol, and properties of the sampled aerosol can thus be inferred. Mass changes within the probe droplet can be measured at the picogram scale. The development and benchmarking of this system and optimisation of the AOT trapping cell to improve accretion efficiency are described. Estimated lowest detectable concentration for a 10-minute sampling period were found to be of the order of 1 mg m⁻³.

A zero particle background environment for measurements of respiratory aerosol from human participants was created by the use of an operating theatre featuring an ultra-clean ventilation system. Measurements of respiratory aerosol produced by singers and instrumentalists are reported, and comparisons and expansions to previous work are discussed. Respiratory aerosol produced by flutes and piccolos was found to be comparable to that produced during breathing, and particles emitted during vocalisation were found to be at a higher concentration and larger size distribution. A strong dependence of concentration on volume was observed.

Date of Award	22 Mar 2022
Original language	English
Awarding Institution	University of Bristol
Sponsors	Defence Science and Technology Laboratory
Supervisor	Jonathan P Reid (Supervisor) & Andrew J Orr-Ewing (Supervisor)