Date of Award
Doctor of Philosophy
Cork Institute of Technology
Dr. Niall Smith
A number of potential methods for the production of multiple light beams for long- path differential absorption spectroscopy have been considered and analysed. The system deemed most suitable has been designed, constructed and tested over two adjacent measurement paths.
The system was built in Cork Institute of Technology to the west of Cork City, Ireland during the period 2000 - 2004. The system has been tested during the winter period of 2003/2004 and ambient concentrations of SO2 and NO2 have been measured and are reported. The measurement of additional gaseous species and suspended particulate matter was excluded from this study owing to the difficulties involved in particle size discrimination via spectroscopic techniques and calibration-related issues. The system has been empirically calibrated using known gas volumes.
The entire instrument is controlled via LabVIEW. This includes data acquisition, hardware interfacing and overall system control, automated data reduction and processing.
Recognised issues with the present design, such as scanning repeatability, image drift, interference from other gases and the physical bulk of the deflection system are highlighted, and modifications and improvements are suggested. The applicability of the system to tomographic reconstruction also considered.
Major findings of this study were: I) modest fixed-grating spectrographs are suited to long-path DOAS applications; 2) CCD arrays are well suited to DOAS applications; 3) the generation of multiple simultaneous light beams from a single light source is complex and; 4) beam deflection works well in conjunction with long-path DOAS. Additional findings include: (i) LabVIEW was found to be well-suited to instrument control and data reduction; (ii) empirical SO2 calibration techniques were found to work well, but worked less well in the case of NO2; (iii) advanced data reduction techniques must be used where a number of species overlap in a particular spectral window but regions of reduced or negligible interference may be used with success; and (iv) the mean concentrations of SO2 were found to be in agreement with the typical values reported by recent EPA and City Council air quality monitoring studies. The mean concentration of NO2 was found to be approximately five times greater than that of SO2 and greater than the recommended EU limits.
Murphy, John Gerard, "Multi-Path Differential Optical Absorption Spectroscopy" (2004). Theses [online].
Available at: https://sword.cit.ie/allthe/691