New research uncovers safety concerns with some air purifiers marketed for COVID-19

PSU researchers help develop tool to guide decision-making

As employers, schools and local governments look to air-cleaning technologies to make spaces safer during the ongoing COVID-19 pandemic, a new study from Portland State University, Illinois Tech and Colorado State University found that some of these technologies may be ineffective — and could have unintended health consequences. The researchers also developed a tool based on these findings to calculate clear air delivery rates of these devices.

The study, published this month in Building and Environment, mimicked real-world operating conditions for these air purifiers that use ionization technology to test the effectiveness and potential to form chemical byproducts in environments similar to where we all live, work and learn. The authors of this research are Aurélie Laguerre and Elliott Gall from Portland State University, Yicheng Zeng, Prashik Manwatkar, Marina Beke, Insung Kang, Akram Ali, Mohammad Heidarinejad and Brent Stephens from Illinois Tech, and Delphine Farmer from Colorado State University.

One of the most popular types of air purifiers on the market right now are ion-generating systems, including ‘bipolar ionization’ devices that electrically charge particles so they settle out of the air faster, and are generally marketed to kill bacteria, fungi and viruses. It’s this “virus-killing” capability that’s been heavily featured in advertising over the past year and led to a flood of new and revamped products on the market.

“There's always been sort of an undercurrent of companies that are making bold claims and aggressively marketing these types of devices,” said Gall, assistant professor of Mechanical and Materials Engineering. “I think because of COVID, it's become a more lucrative market and there’s a lot more interest.”

However, the study found that the air purifier marketplace is fraught with inadequate test standards, confusing terminology, and a lack of peer-reviewed studies of their effectiveness and safety. Unlike air filtration, where air is pushed through a filter to remove airborne pollutants, there has been very little research on the effectiveness and side effects of “additive” air cleaning methods like ionizing devices. 

For this study, researchers conducted chamber and field experiments to better understand the “real world” effects of these air cleaning systems.

“Laboratory and field measurements showed similar conclusions: the devices may not be as effective at removing particles as expected and our data suggests the formation of some byproducts that could potentially be harmful and/or react with other compounds,” said Aurélie Laguerre, research analyst in PSU’s Healthy Buildings Research Laboratory. “There’s a need for more research on this topic as well as for standardized test methods for evaluating the efficacy and potential for byproduct formation of these devices.”

Gall said at PSU, researchers wanted to take these initial findings and build a tool for people like school board members who will be tasked with making decisions about air cleaning systems as students transition to in-person learning. The tool, available at, allows anyone to determine a device’s equivalent clean air delivery rate using the manufacturer’s data.

“There’s a reason some manufacturers are not presenting the clean air delivery rate or an equivalent metric that enables scaling to an indoor space — many ionizers and additive air cleaners don’t perform well at building-scale,” Gall said. “Companies that manufacture air cleaners should be providing consumers data that enables an estimation of the expected efficacy of the device in a realistic indoor space.”

This information is especially important, Gall added, because the recently passed American Rescue Plan Act includes funding for buildings to improve air quality.

“There’s an opportunity to improve air quality and these systems have the potential to influence people’s health and lives,” he said. “There’s a lot at stake.”