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Title: Evaluation and application of FTIR spectroscopy for field study of biomass burning emissions
Author: Smith, Thomas
Awarding Body: King's College London (University of London)
Current Institution: King's College London (University of London)
Date of Award: 2013
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An average of 3.5-4.5 million square km of vegetation burns in global wildfires each year. The gases and particulates released have substantial chemical and radiative impacts, the magnitude of which depends on the specific makeup and magnitude of the emissions. This research focuses on the development, evaluation and application of field-deployed methods based around Fourier transform infrared (FTIR) spectroscopy for the assessment of the emissions from biomass burning events. In particular, full assessment of the atmospheric effects of biomass burning generally requires spatio-temporally resolved data on the makeup and magnitude of the smoke emissions. This is usually obtained via multiplication of the amount of fuel consumed [M] by an emission factor [EFX], representing the amount of chemical species [x] released per kilogram of dry fuel burned. Emissions factors for many species typically show wide ecosystem variations, and also vary with meteorology and fire type, increasing the uncertainty in this important variable. When compared to established point-sampling methods, OP-FTIR spectroscopy can measure many different gases simultaneously, in situ and near-continuously, and can provide path-integrated amounts. Few studies, however, have investigated the accuracy of the retrievals of the main biomass burning gases (CC>2, CO and CH4), particularly across the broad range of concentrations found in ambient air to biomass burning plumes. Laboratory gas cell experiments were first used to evaluate the accuracy of the FTIR spectrometer and spectral analysis methodology deployed to retrieving concentrations of these gases at open biomass burning sites. The findings suggest that with optimisation of the retrieval parameters, column amounts accurate to within 5% can be confidently derived. During 2009-2011, the FTIR equipment was deployed to a number of experimental fires for the purpose of improving our understanding of emission factors. Three case studies are presented in this thesis: 1. Determining the seasonality of biomass burning emissions in Australian savanna lands - Seasonal (early- and late-dry season) emission factors were measured and compared, revealing no evidence of seasonality of emissions, in contrast to some previous works. Instead, Modified Combustion Efficiency explains most of the variation (e.g. 95% for CH4) in emission factors 2. Building an emissions inventory for UK fuel types - Emission factors for heather (Calluna vulgaris) were measured here for the first time, enabling the first measurement-based estimates of total UK biomass burning emissions for the main carbonaceous gases and selected volatile organic compounds. Typical flaming combustion emission factors for CC>2, CO, CFLt and NH3 are around 1711, 66.2, 2.8 and 0.53 g kg"1 dry fuel combusted, respectively. 3. Determining emission ratios using solar occultation FTIR spectroscopy of lofted plumes from large wildfires in the Northern Territory, Australia, and comparison of total column trace gas amounts with simultaneous and collocated measurements of Aerosol Optical Depth (AOD). The emission ratio of NH3 to CO determined from solar measurements is shown to agree with that measured on the ground using OP-FTIR. A relationship is established between total column amounts of CO and AOD, confirming that satellite-derived measures of AOD could be used as a proxy for trace gas amounts. Further work includes an exploration of the use of field-deployed FTIR in the study of aerosols in biomass burning plumes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available