A fibre- optic sensor for the monitoring of hazardous vehicle exhaust emissions of the order of parts per million ( PPM) is described and tested. The sensor based on absorption in the ultraviolet region is used to simultaneously measure the concentrations of three of the major exhaust emission gases and output them to the vehicle's on- board computer. Experimental results describing the operation of this sensor with nitrogen dioxide ( NO2), sulfur dioxide ( SO2) and nitric oxide ( NO) are shown. The sensor was found to have a lower threshold of detection for NO2 of 2 ppm, SO2 of 2 ppm and NO of 20 ppm. The sensor showed response times of less than four seconds and demonstrated minimal susceptibility to cross interferences of the gases.