Effect of an ionic air cleaner on indoor/outdoor particle ratios in a residential environment

We tested a leading commercially available ionic air cleaner in a typical residential apartment to study the effect of the device on indoor/outdoor airborne particle number and mass concentration ratios. In addition, we also determined the indoor ozone and ion concentration levels. When measured during normal daily activity, the average indoor/outdoor mass concentration ratio was reduced from 1.03 to 0.73 and the number concentration ratios underwent reductions for most of the particle size fractions. However, due to a substantial inter- and intra-measurement variation in particle ratios, the observed average reductions were not statistically significant. When measurements were performed in a still room, the indoor/outdoor particle mass concentration ratio decreased from 0.9-1.4 to 0.3-0.4 in eight hours when the air cleaner was operating. Ambient ozone concentrations measured in the middle of the apartment were between 13-19 ppb during normal daily activity and the ozone levels increased to 77 ppb when measured in front of the ionic cleaner during still conditions. We also found that that there was a limited vertical diffusion of ions. The highest ion concentrations were measured at a 0.5 m height from the floor and decreased substantially with increasing measurement height. This finding may have implications for effective particle removal from a person's breathing zone. Overall, we found that the tested brand of commercially available ionic air cleaners may have the capability to remove some airborne particulate matter in actual residential settings, but its cleaning effect is reduced under normal daily activity.