Ultrafine particle removal and generation by portable air cleaners

Abstract Portable air cleaners can both remove and generate pollutants indoors. To investigate these phenomena, we conducted a two-phase investigation in a 14.75 m3 stainless steel chamber. In the first phase, particle size-resolved (12.6–514 nm diameter) clean air delivery rates (CADR) and efficiencies were determined, as were ozone emission rates, for two high-efficiency particle arresting (HEPA) filters, one electrostatic precipitator with a fan, and two ion generators without fans. The two HEPA air cleaners had count average CADR (standard deviation) of 188 (30) and 324 (44) m3 h−1; the electrostatic precipitator 284 (62) m3 h−1; and the two ion generators 41 (11) and 35 (13) m3 h−1. The electrostatic precipitator emitted ozone at a rate of 3.8±0.2 mg h−1, and the two ion generators 3.3±0.2 and 4.3±0.2 mg h−1. Ozone initiates reactions with certain unsaturated organic compounds that produce ultrafine and fine particles, carbonyls, other oxidized products, and free radicals. During the second phase, five different ion generators were operated separately in the presence of a plug-in liquid or solid air freshener, representing a strong terpene source. For air exchange rates of between 0.49 and 0.96 h−1, three ion generators acted as steady-state net particle generators in the entire measured range of 4.61–157 nm, and two generated particles in the range of approximately 10 to 39–55 nm. Terpene and aldehyde concentrations were also sampled for one ion generator, and concentrations of terpenes decreased and formaldehyde increased. Given these results, the pollutant removal benefits of ozone-generating air cleaners may be outweighed by the generation of indoor pollution.