A comprehensive study of DC discharges in pure O2 gas in a Pyrex tube is presented using a range of diagnostics. Fourier-transform vacuum ultraviolet absorption spectroscopy (FT-VUVAS) provided high-resolution (106) spectra in the region 120-170 nm of O2 (X), O2 (a), O2 (b) and ground state O atoms, allowing their absolute densities to be determined. Optical Emission Spectroscopy (OAS) was used to determine the gas temperature from the O2 (bX) emission spectrum. Time-resolved OAS of partially-modulated discharges was used to probe the loss rates of O2 (b) and of O atoms. From these measurements the surface loss coefficients of these species can be determined, as well as the rate constants for electron impact dissociation of O2. A remarkable increase in the surface loss coefficient on Pyrex of O2 (b) and O atoms is observed at low pressures, corresponding to the onset of energetic ion bombardment.