Development, Characterisation and Implementation of Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry for the Measurement of Atmospheric Volatile Organic Compounds.

Volatile organic compounds (VOCs) are ubiquitous within the Earth’s troposphere, being released both locally and globally from anthropogenic and biogenic sources. VOCs constitute an important class of reactive trace species responsible for the production and exacerbation of numerous documented atmospheric issues, including photochemical production of ozone and formation of secondary organic aerosol (SOA). Consequently, measurement of VOCs under both ambient and laboratory conditions is crucial, such that emissions controls may be affected, environment response may be monitored and scientific understanding of the atmosphere may be advanced. This thesis describes the development, characterisation and application of a novel technique for ‘real-time’ detection of atmospheric VOCs. Termed Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), analyte ionisation by ion-molecule interaction is employed under defined reaction conditions, followed by TOF mass spectrometric analysis. Within this work CIR-TOF-MS is comprehensively characterised for the detection of a wide range of atmospheric VOCs using the chemical ionisation reagent ions H3O+, NH4+, NO+ and O2+•. Reaction products and species-specific markers are identified for future use and ionisation mechanisms are explained. Detailed investigations into instrument performance and optimisation are described, and compound specific sensitivities and detection limits are determined. The technique is validated for quantitative atmospheric monitoring using findings from a multi-institution measurement intercomparison. It is shown that VOC measurements are made by CIR-TOF-MS with a high level of accuracy and precision. CIR-TOF-MS is also applied for the first time to urban air monitoring, where typical ‘city’ VOC pollutants are measured in high detail. The work presented culminates with a comprehensive description of the first major application of CIR-TOF-MS to the scientific exploration of a contemporary atmospheric issue: SOA formation. CIR-TOF-MS measurements provide key insight into the identity of potential SOA contributing compounds, including a number of previously unobserved molecules. Findings also provide support to current understanding of gas phase VOC degradation mechanisms.