Evaluation of sensor-based air cleaners to remove PM2.5 and TVOC from indoors with pollutant sources of smoking and burning candles

Indoor air quality in residential buildings has been attracting more attention from the public. Many portable air cleaner products have been developed and are available in the market. Manufactures generally claim that those portable air cleaners can efficiently remove PM2.5 and/or TVOC and can also remove virus from the indoor air. However, no standards are available to have the claimed efficiency comparable and thus unclear effect in applications at homes. This study tested four air cleaners with embedded sensors by using pollutant sources of smoking and burning candles, which exist widely at homes, in a climate chamber (20 m3) without turning on the mechanical ventilation system, respectively. The concentrations of PM2.5 and TVOC measured by the embedded sensors were compared with the recorded data by instruments with high accuracy such as DustTrak (8533), SMPS (scanning mobility particle sizer, 3910), OPS (optical particle sizer, 3330) and Ion Science Tiger TVOC gas detector. The results showed that the embedded sensors generally underestimated the PM2.5 mass concentration and thus influenced the regulation of fan speeds of air cleaners. Only the embedded sensor of one air cleaner could provide comparable PM2.5 mass concentration with the data measured by DustTrak when the concentration was within the detected range of the embedded sensor (< 1000 μg/m3). The underestimated PM2.5 mass concentrations led to the air cleaners to quickly switch to the lowest fan speed although the PM2.5 mass concentration was still far too high. The embedded sensors cannot properly detect the mass concentrations of ultrafine particles released from burning candles. The air cleaners do not regulate its fan speeds based on TVOC concentrations measured by the embedded TVOC sensors. The obtained results highlighted the limited accuracy of the embedded low-cost sensors. It is imperative to issue standards to guide manufacturer to properly report the efficiency of their products and to clearly claim the performance of air cleaners.