Characterisation of urban and remote atmospheres using comprehensive two dimensional gas chromatography

Volatile organic compounds (VOCs) are key precursors to ozone and particulate matter, two of the most important air pollutants. Air quality interventions have successfully reduced the release of short chain VOCs in urban areas. The increased use of diesel vehicles has created an increase in the direct emission of longer chain VOCs. However, these compounds are not considered as part of air quality strategies and there are few atmospheric measurements of them to date.

This thesis details continuous measurements of VOCs in London, a developed megacity, using comprehensive two dimensional gas chromatography. Analysis of this large suite of VOC measurements have shown that the higher carbon number species emitted from diesel vehicles can dominate gas phase reactive carbon in cities with a significant diesel fleet. Comparison of these real-world observations with emissions inventories has highlighted that there is a significant under prediction of the emissions of higher carbon number species. This presents a considerable policy challenge; the focus must now switch to VOCs released from diesel as this vehicle type is increasingly replacing gasoline world-wide.

Further analysis of the London data has provided evidence of both anthropogenic and biogenic emission sources. The measurement of the higher carbon number species has allowed for OH reactivity to be more accurately modelled. Detailed analysis of the ethanol observations provided direct evidence that the use of bio-ethanol blended gasoline in the UK is having an impact on the composition of the atmosphere.

The combination of heart-cut and comprehensive two dimensional gas chromatography into a single instrument has made the measurement of both small and large chain VOCs possible. This instrument compares well to existing instrumentation and when deployed to a rural location (Bachok, Malaysia) provided hourly time-resolved measurements of C5-C13 VOCs.