Initial efficiencies of air cleaners for the removal of nitrogen dioxide and volatile organic compounds

The objective of this research was to measure the initial effective cleaning rates (ECRs) of selected air cleaners for removing nitrogen dioxide (NO₂) and six representative volatile organic compounds (VOC) from air. Four portable air cleaners, representing different principles of particle removal and incorporating activated carbon, were investigated. Experiments were conducted in a closed room-size environmental chamber using analyte concentrations similar to those reported in residences. Effects of relative humidity, temperature, filter particle loading and saturation of the adsorbents on the ECRs were not investigated in this preliminary study. However, the effect of extended usage was investigated for one air cleaner.

Two of the air cleaners were found to be reasonably effective initially in removing NO₂ and five of the six VOC. These two devices had relatively high flow rates and the greatest amounts of activated carbon. None of the devices removed dichloromethane, the VOC with the highest vapor pressure. One air cleaner emitted 1,1,1-trichloroethane and formaldehyde. After being used in a residence for 150 h, the ECRs for the air cleaner which had the highest initial values decreased to 50% or less of the initial ECRs. This use was only about 15% of the recommended filter lifetime. Conversion of NO₂ to NO was also observed for this device but only after it had been used in the residence.