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 NO 2 SO 2 , and NO are shown. These experimental results are compared with existing published spectroscopic absorption measurements. It is shown that the minimum detectable concentration of NO 2 is 1 ppm, SO 2 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. Index Terms-differential optical absorption spectroscopy (DOAS), exhaust gas sensing, pollution monitoring, spectroscopy, ultra-violet (UV).