Contextualizing Equivalent Clean Airflow Rates for Airborne Pathogens of Ionizers and Other Electronic Indoor Air Cleaners

Abstract

Additive electronic air cleaners like ionizers, photocatalytic oxidizers, and plasma devices intentionally release reactive species into indoor air so that they may inactivate infectious airborne pathogens. Third-party commercial testing and peer-reviewed studies alike typically report inactivation metrics in terms of percent- or log-reductions observed from chamber experiments that imply a nearly complete elimination of infection risks. However, these metrics are highly dependent upon the experimental volume and duration, so they do not directly translate to actual effectiveness indoors. We reviewed 45 experiments across 14 published studies and converted reported reduction metrics into equivalent clean airflow rates (ECA). Different studies yielded distinct ECA distributions, suggesting that differences in experimental procedures, device specifications, or environmental conditions may be more important ECA determinants than the target pathogen or the underlying device technology. Study-averaged ECAs spanned between 1.4 and 134 m3/h, with the median study having an average ECA = 31 m3/h. Even small off-the-shelf HEPA-filter air cleaners typically provide ECAs that exceed the best-performing additive devices analyzed herein. Their low efficacy relative to alternatives, environmental factors that can affect performance, and chemical byproduct concerns are discussed in the context of test standard development and system selection.