Removal of volatile organic compounds by mobile air cleaners: Dynamics, limitations, and possible side effects

Air cleaners are becoming increasingly popular as a response to the increased focus on the impact of indoor air quality on human health, comfort and performance. In this study, the removal of particulate matter (PM) and volatile organic compounds (VOCs) by mobile air cleaners is investigated in an unoccupied university classroom. From time-resolved measurements by proton-transfer-reaction time of flight mass spectrometer (PTR-TOF-MS) the study reports on VOC removal and by-product formation from different air cleaning technologies. Results revealed an inconsistency between expected and experimentally obtained clean air delivery rates (CADRs). For seven out of eight air cleaners examined, the CADRs for all VOCs tested (methanol, acetaldehyde, acetone, acetic acid, isoprene, butanone, toluene, benzaldehyde and limonene) were significantly lower than the corresponding CADRs for PM. In general, single pass removal efficiencies (REs) for VOCs were found to decrease as a function of time. The VOCs demonstrated very distinctive dynamic behavior. Results indicated adsorption as the main removal mechanism of VOCs for all air cleaners for which a significant removal (RE >= 5%) was observed. Formation of by-products (incl. CH2O and C4H6O) was associated with technologies containing an UV lamp. Reemission of specific VOCs was observed for adsorption-based air cleaners during operation in a newly vented room. The results highlight the inadequacy of how we currently report air cleaner performance.