Novel Integrated Approaches to Greenhouse Gas Sensing

Abstract

The effects of anthropogenic climate change pose significant risks to the environment and human property, with the most serious being loss of life. Addressing this issue requires accurate monitoring of all greenhouse gases, including trace gases like methane and nitrous oxide, which are difficult to detect at low concentrations. Studies suggest human activities release more of these gases than previously estimated, creating an urgent need for improved, lightweight, portable detectors that can cover large areas while maintaining high selectivity and sensitivity. Absorption spectroscopy enables precise gas detection, with modulation spectroscopy offering sensitive, low-cost solutions. This thesis explores two applications of modulation spectroscopy for "fingerprint" gas detection—highly sensitive and selective molecular species identification and monitoring. The first focuses on cross-correlation using a complex aperiodic fiber Bragg grating (FBG) that mimics acetylene’s P-band absorption features. We demonstrate, for the first time, that complex FBGs can selectively identify different gas concentrations while maintaining high selectivity. Simulated data reinforce these findings, highlighting the potential for selective gas detection. The second part investigates wavelength modulation spectroscopy through quartz-enhanced photoacoustic spectroscopy (QEPAS). QEPAS generates sound waves from modulated light interacting with the target gas, with a quartz tuning fork (QTF) converting these waves into electrical signals. This thesis presents dedicated voltage amplifiers to enhance the QTF’s piezoelectric signal and two custom-built QEPAS units using 3D-printed materials for methane detection. These chambers incorporate chemical annealing for improved material finish. A direct amplifier comparison demonstrates methane detection with a minimum detection limit of 6.4 ppm, showcasing a practical, customizable approach for sensitive gas detection.