Assessing the performance of portable gas-phase air cleaners and Implications for their use in buildings

We examined the performance of two different brands of gas-phase air cleaners using Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) measurements; both air cleaners used activated carbon filters. The measurements were made in a typical office with furnishing and two occupants. The air cleaners were examined under multiple airflow settings and with different numbers of active units. The distinct non-negligible 44 mass-to-charge ratio (m/z) signals for ions representing various organic compounds or their fragments were identified by PTR-ToF-MS. Operation of air cleaners consistently reduced the magnitude of twenty-two of them. We analysed the decay of the m/z signals to characterize the performance of air cleaners in terms of their pollutant removal effect. We observed that it was different for the different m/z signals, suggesting different removal efficiencies for various compounds or their fragments. Removal efficiency decreased with higher airflow rates through the air cleaners though the rate of clean air delivered by them was higher. Our results document that describing the performance of gas-phase air cleaners must include reporting of removal effects for different organic compounds along with the clean air delivery rate. Alternatively, target compounds can be identified and their removal efficiencies reported together with the air cleaning effect. The present work describes the methodological approach that can guide the revision of current practice and standards for evaluating the performance of gas-phase air cleaners. More studies using this methodological framework can lead towards greater adoption and use of gas-phase air cleaners in sustainable and healthy buildings.