Detection of Aerosols via Coalescence Capture

  • Lilly Manzoni

Student thesis: Master's ThesisMaster of Science (MSc)

Abstract

The detection of Chemical Warfare Agents, CWAs is vital in order to reduce the life limiting and harmful effects of CWAs on the surrounding populations. The work in this thesis was done to further assess the potential of the aerosol optical tweezers (AOT) approach for the real time sampling of CWAs. This application of the AOT technique is unique and the detection of CWAs in real time, with low false alarm rate and high sensitivity, is difficult to achieve. There are a limited number of techniques which can detect aerosol phase CWAs and the AOT technique was found to have potential in this application. To assess the potential for application to this problem, the baseline sensitivity
of the AOT technique was established using statistical and experimental analyses. The baseline sensitivity was determined, on both a commercially built system and a purpose-built research grade instrument. The two instruments were compared and a protocol for assessing the sensitivity of future AOT instruments was established. As part of the sensitivity analysis, using an Allan variance analysis, the components of noise in an AOT dataset were characterised and the optimal sampling time of 40 seconds per spectra was
determined, and the recommended probe droplet size range was 4 – 5 micrometres.

Additionally, this work investigated the physical design constraints of an AOT instrument for the detection of CWAs. A range of methods for delivering humidifying gas flow, and sample aerosol to a probe droplet were compared. It was recommended that the sample aerosol is delivered as a minor component of a gas flow. Finally, this work performed
accretion measurements on an AOT instrument with observed accretion rates of between1.7 × 10-4 to 0.2 pg s-1. The sampling aerosol, the probe droplet, was exposed to was characterised using an optical particle sizer and a Nanoscan scanning mobility particle sizer. This work seeks to fully characterise the noise characteristics of an AOT instrument, and to understand what steps can be taken to improve the sensitivity of the technique. This work seeks to test the ideal layout of the AOT instrument for the detection of an ensemble of aerosol using an optically tweezed droplet
Date of Award25 Sep 2018
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJonathan P Reid (Supervisor)

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