Portable air cleaners are designed to remove airborne pollutants, but some types of air cleaners can emit or induce pollutants. This research was aimed at evaluating the performance of portable air cleaners in terms of a clean air delivery rate (CADR) for removal of fine particles and to measure ozone emission. The study was extended to investigate ozone-initiated pollutants from the use of an in-car ion generator in the presence of synthetic and natural air fresheners. The tested air cleaners included four household brands and two in-car brands. The experiments were conducted in an 8 m3 chamber. The CADRs and ozone emission rates of the tested air cleaners were determined by fitting time-dependent concentrations to mass balance models using a least-squares method. The CADRs for the household air cleaners using the HEPA and electrostatic precipitator ranged from 14 to 62 m3 h-1, while the ozone generator and the in-car ion generators were found to have negligible CADRs. The ozone generator, ion generators, and electrostatic precipitator emitted ozone at the rates of 55.7, 1.94, and 0.92 mg h-1, respectively. The use of the lemon-scented air fresheners in the presence of the in-car ion generator resulted in the substantial increases of formaldehyde, acetaldehyde, acetone, and PM2.5, while screw pine leaves and camphor did not increase the pollutants. ? 2013 The Author(s).