Terahertz spectroscopy of nitric oxide for emissions monitoring in bioenergy systems

Abstract

II tc aAtsb AThe aim of this thesis is to study pollutants that are emitted from combustion systems using Terahertz time domain spectroscopy (THz-TDS). In particular, this thesis will focus on Nitric Oxide (NO), which is present in flue gases and contributes to air pollution. It is also interesting from a Physics perspective because it contains an unpaired electron in the valence shell, which leads to a complicated energy level structure, and interesting Physics.In this thesis, we aim to answer the question: "what is the detection limit of NO, using THz-TDS, and is it suitable for industrial emissions monitoring?" It is therefore necessary to look at detection limits, which in turn requires conducting THz spectroscopy at different gas pressures.A gas-cell containing NO is used in a THz-TDS set-up, where the temporal and spectral response of a THz pulse propagating through a gas sample of NO molecules is probed. A theoretical model for the interaction between the THz radiation and NO is developed, taking into account the complicated molecular structure of NO. A direct comparison is then made between the experimental data and our theoretical model. The good agreement between theory and experiment allows us to project the limits of detection for NO sensing that is possible with commercially available THz systems today, and the potential for the technology to be used in harsh environments is discussed. III List of papers1-"Terahertz spectroscopy of wood and combustion gas," M. Reid, T. Inagaki, S.