Dimethyl methylphosphonate (DMMP) removal by a continuous photocatalytic reaction system at different levels of humidity (RH) was investigated for the purpose of allowing rescue operations at disaster sites over an extended period of time when applied to gas masks or other protective gear. With a high flow rate of air (10 L/min), around 85% of the 0.17 mu mol/L DMMP was successfully eliminated by this photocatalytic reaction system regardless of relative humidity. On the other hand, the formation of intermediates on the TiO2 surface indicated that photocatalytic activity was dependent on relative humidity, and during a 5-h test period, the ratio of photocatalytic DMMP conversion reached 74.5% at 100% RH. DMMP adsorption onto the TiO2 surface was found to be quite strong; DMMP removal was observed despite low humidity and dark conditions (C) 2013 Elsevier B.V. All rights reserved.