Deep UV based DOAS system for the monitoring of nitric oxide using ratiometric separation techniques

The investigation of an ultra violet DOAS (differential optical absorption spectroscopy) sensor based on fibre-optic technology for the monitoring of nitric oxide gas in an exhaust environment is described. Cross-sensitivity issues with other gases present in the environment were realised and ratiometric separation techniques were developed in order to reduce the sensor's susceptibility to these interferences. Experimental results describing the calibration of the sensor against a commercial analyser and tests documenting the sensor's operating capabilities within the exhaust of an engine are presented. The lower limit of detection for the sensor was found to be 5 ppm with response times of 3.4 s.