Stand Alone Air Cleaners: Evaluation and Implications

Stand alone (portable) air cleaners may be an efficient means for rapid removal of indoor fine particles, with potential use for shelter-in-place strategies following acts of bio-terrorism. In this study, a screening model was developed to ascertain the potential significance of size-resolved particle removal using portable air cleaners relative to filtration in HVAC systems, deposition to indoor surfaces, and air exchange. The air exchange rate, volumetric flow rate through the HVAC system, and size-resolved particle removal efficiency in the HVAC filter were varied. The effectiveness of portable air cleaners depends on size specific clean air delivery rates CADR. Since these values were not readily available in the published literature, we used experiments to determine ranges of CADR based on three air cleaners that had been in use in residential homes. Experiments were completed in a well-mixed 11-m3 stainless-steel chamber. Incense sticks were burned for five minutes during each experiment, resulting in a poly-disperse aerosol with a wide range of fine particle diameters. Particle number concentrations were measured for seven ranges of particle diameter consistent with those expected for biological warfare agents. The effects of chamber air exchange, deposition, and coagulation were separate