We have developed a versatile measurement system utilising field asymmetric ion mobility spectrometry (FAIMS) to study the photocatalytic degradation of VOC’s at concentrations comparable to indoor air. FAIMS allows continuous monitoring of chemical species in the gas phase, whilst having a high separation selectivity and sensitivity, so can be used to identify multiple species concurrently at ppb concentrations, which are clear advantages over traditional characterization techniques used in photocatalytic air purification such as gas chromatography. Here we demonstrate the methodology with the photo-oxidation of 2-propanol, ethanol and acetone using a commercial titanium dioxide felt. To the best of our knowledge, this is the first time FAIMS has been used in photocatalytic air purification applications.