What Air Purifier should you buy? This was deliberate: It put the particle counter well outside the airflow path from the purifiers, to avoid an artificially high measure of their performance, and, instead, measured the air a typical adult would be breathing at standing height at the far end of a typical bedroom.On pure air-cleaning performance, it outdid the Coway, reducing particulates by more than 99 percent on both high and quiet” (medium) settings in the New York test room thanks to its high airflow and a clever and effective electrostatic mechanism that improves its capture of fine particles.