Abstract The chemical kinetics of oxygen atoms and ozone molecules were investigated in a fullymodulated DC discharge in pure oxygen gas in a borosilicate glass tube, using cavity ringdown spectroscopy (CRDS) of the optically forbidden O(3P2)->O(1D2) absorption at 630nm. Measurements were made over a range of tube temperatures (10 and 50°C) gas pressures (0.5-4 Torr) and discharge current (10-40 mA). The discharge current was square-wave modulated (on for 0.2 seconds and off for 1 second), allowing the build-up to steady state and the decay in the-afterglow to be studied. This paper focusses on the afterglow period. The O atom density decays non-exponentially in the afterglow, indicating a surface loss probability dependent on incident active particle fluxes. The oxygen atom absorption peak lies on a time-varying absorption continuum due (in the afterglow) to the Chappuis bands of ozone. The ozone density passes through a maximum a few 100ms into the afterglow, then decays slowly. An existing time-resolved self-consistent 1D radial model of O2 positive column discharges was modified to interpret the new results. The ozone behaviour in the afterglow can only be modelled by the inclusion of : 1) surface production of O3 from the reaction of O2 molecules with adsorbed O atoms, 2) reactions of vibrationally-excited ozone with O atoms and with O2(a1∆g) molecules, and 3) surface loss of ozone with a probability of around 10-5.