The development of an ultra-violet (UV) differential optical absorption spectroscopy (DOAS) fibre-optic sensor for the monitoring of vehicle exhaust gases is described in this paper. Experimental results describing the operation of this sensor with NO2, SO2, and NO are shown. These experimental results are compared with existing published spectroscopic absorption measurements. It is shown that the minimum detectable concentration of NO2 is 1 ppm, SO2 is 1 ppm, and NO is 26 ppm. The sensor was found to have a low susceptibility to interference between the detection of these gases.