 The forced flow of air or water through this environment ensures exposure.The effectiveness of germicidal UV depends on the length of time a microorganism is exposed to UV, the intensity and wavelength of the UV radiation, the presence of particles that can protect the microorganisms from UV, and a microorganism's ability to withstand UV during its exposure.In many systems, redundancy in exposing microorganisms to UV is achieved by circulating the air or water repeatedly.