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3.3 HEALTH SCIENCES
Monitoring of air pollutants, such as Nitrogen Dioxide (NO2), that are toxic or environmentally damaging is a key metric for environmental protection agencies worldwide. There is a constant need to develop new technologies and methodologies that provide real-time, low cost pollution measurements over a broad range of sampling sites, particularly in urban and industrial areas. Typically, detection of pollutants in urban environments is performed using a variety of techniques, many of which are expensive, require complex setups and are in fixed locations. The novel system presented in this thesis is designed for portable, low cost and in-situ detection of pollutants such as NO2 using Differential Optical Absorption Spectroscopy (DOAS). The basis for the system is the new generation of miniature fibre optic spectrometers that provide measurement specifications close to those of more traditional high cost DOAS instruments which are used to cross calibrate the initial data. The system can also be calibrated against other NO2 sampling techniques such as chemiluminescence (CL) monitors. Based on laboratory calibration, the final measurement accuracy of the system in the field was less than ± 0.5 ppb over a calibration dynamic range of 0-50 ppb under typical daylight conditions. This level of accuracy was achieved with repeated measurements, n=10, of custom made calibration cells containing known concentrations of NO2. Laboratory experiments using a controlled light source were designed to examine the correlation between absorption and differential absorption using the NO2 calibration cells with an algorithm based on the Beer-Lambert Law. These laboratory calibration tests verified that differential absorption determined using the novel system can be used to quantify NO2 concentrations both in the laboratory and in the open atmosphere of a surrounding urban area. Field tests, using ambient sunlight as a source, were then conducted and compared to concurrent CL measurements. Good correlations have been confirmed between the novel-DOAS data and the established NO2 quantification methods. Results prove that low cost spectrometer systems can be used to identify and quantify gaseous pollutants in real-time using ambient sunlight.
Devine, B. (2013). A Miniaturised Spectrometer Device for the Detection of Nitrogen Dioxide in an Urban Environment. Doctoral Thesis. Dublin Institute of Technology. doi:10.21427/D79594