This paper reports a spectroscopic study of non-thermal plasma chemistry in an air-fed dielectric barrier discharge (DBD) plasma jet. In situ analysis (i.e. the analysis of the plasma glow) and downstream analysis were carried out to identify and monitor species produced in the plasma as they propagate from the plasma glow to downstream regions. The analyses were carried out using Fourier Transform InfraRed (FTIR) and UV–Vis spectroscopies. The species: O 3 , N 2 O 5 , N 2 O, HNO 3 , CO 2 , CO and, for the first time, a vibrationally excited form of CO 2 (i.e. CO 2 ∗ ( v )) were identified in the plasma glow, while O 3 , N 2 O 5 , HNO 3 and N 2 O were detected in the downstream exhaust. The behaviour of these species was monitored as a function of a range of experimental conditions including: input power, gas flow rate, relative humidity, gas temperature and feed gas composition. In addition, the uncertainty associated with UV–vis detection of ozone in the presence of N 2 O 5 and/or HNO 3 as interfering species was determined.