Efficiency of portable HEPA air purifiers against traffic related combustion particles

Exposure to diesel combustion particles is known to cause and exacerbate respiratory conditions, including asthma. High efficiency particulate air (HEPA) purifiers can provide health benefits by reducing concentrations of these particles. National standards call for air purifiers to be tested using tobacco smoke, as well as aerosolized dust, pollen, and potassium chloride (KCl) particles. Little is known about the efficiency of HEPA air purifiers against diesel particles. Previous studies performed with respirator filters have shown higher penetration of combustion generated particles compared to standard test particles. Within a controlled laboratory setting, we compared the Clean Air Delivery Rate (CADR) of six models of air purifiers with diesel and KCl particles, and measured noise during operation. CADR was determined for total concentration and size-selectively for particles of 0.03-1 μm. Lowest CADRs were consistently found for particles <0.1 μm. Results showed significant differences between CADRs obtained with diesel and KCl aerosols. This was found for CADRs calculated from total concentration data as well as from size-selective data. Unexpectedly, CADR for diesel exceeded the one for KCl particles indicating lower penetration of diesel particles through the HEPA filter. It was concluded that KCl particles may underestimate the actual CADR against diesel particles. The measurements of noise levels produced by the tested air purifiers revealed a low positive association between noise and CADR (r2 = 0.55). Thus, both noise and CADR should be considered when selecting an air cleaner.