Evaluation of an in-duct bipolar ionization device on particulate matter and gas-phase constituents in a large test chamber

Abstract

Bipolar ionization has seen a rapid increase in use for indoor air cleaning, although data on its efficacy and potential for chemical byproduct formation remain limited. We evaluated the impacts of a commercially available bipolar ionizer on particles, ozone, and volatile organic compounds (VOCs) including aldehydes in a large recirculating test chamber. We conducted a combination of natural (only material emissions) and perturbation (particle injection by burning incense) tests under both short-term (∼4 h) and long-term (24+ hours) operation to evaluate the impacts of ionizer operation on pollutant concentrations and loss rates. A subset of tests was also conducted with different fibrous media particle filters installed on the recirculating air stream to explore the potential for ion-assistance of conventional filters. The mean negative ion concentration in the chamber during ionizer operation was ∼9400 ions/cm3. Inside/outside (I/O) chamber concentration ratios and net concentration changes of several VOCs decreased during ionization, while some increased. Many VOC comparisons were within propagated analytical uncertainty, suggesting no discernible impacts on those compounds. Operation of the ionizer by itself or with a mechanical filter with a minimum efficiency reporting value (MERV) of 8 installed in the air stream negligibly impacted particle concentrations and particle loss rates compared to ionizer off conditions. Operation of the ionizer with a MERV 10 or MERV 13 particle filter with electrostatically charged media installed in the air stream led to a modest increase in particle loss rates, which led to an absolute increase in estimated PM2.5 removal efficiency of ∼8–10% compared to ionizer off conditions.