Ohita: A Wearable, Portable Air Filter for City-Dwellers It's pretty easy to control the air quality in your home; But in public places it isn't so easy. Enter the Ohita, a portable air purifier designed by Jorge Alberto Treviño Blanco, an industrial design student in Mexico who suffered asthma attacks that were brought on by smog and air pollution....e-mail: wal954@mail.harvard.edu.AbstractWe validated the use of the mass balance model to determine the effectiveness of portable air purifiers in removing ultrafine (<0.10 μm) and submicrometer particles (0.10–0.53 μm) in an apartment. We evaluated two identical portable air purifiers, equipped with high efficiency particulate air filters, for their performance under three different air flow settings and three target air exchange rates: 0.60, 0.90, and 1.20 h–1. Our study design can be applied to investigate the performances of other portable air purifiers as well as the influences of various parameters on effectiveness in different residential settings.