The tests began simply: see how well four indoor air cleaners could remove toluene and limonene, two common volatile organic compounds (VOCs) from a room. From there, MIT researchers let the devices work their magic. However, after nearly 90 minutes of running, something was amiss. While only two of the devices had been able to completely clean their respective spaces of the targets, all four had managed to introduce new pollutants into the space.
In fact, even when looking at the successful air cleaners, it turns out that their success came with a slight asterisk. While they were successful in removing the targeted VOCs, it wasn’t the marketed oxidation process that was responsible. Instead, the accompanying filter did most of the heavy lifting.
This didn’t come as much of a surprise to the MIT researchers who conducted the study, but it did highlight the reason as to why the study needed to happen in the first place.
“During the pandemic, air cleaners have appeared like mushrooms after days of rain, and sadly, some of these air cleaners can introduce chemicals to indoor air that are of greater concern than the chemicals that they might remove,” says Charles Weschler, an expert on indoor pollution at Rutgers University and Technical University of Denmark, who was not an author of the study. “The paper by Jesse Kroll and co-workers is an excellent demonstration of this fact. It is carefully executed, and the results are clearly and thoughtfully presented.”
The Issue with Oxidation
With the pandemic came a renewed focus on air in the home, and while viral pathogens remain a consideration in air quality, the role VOCs play have gained prominence as well. Whether its from a fresh stain, a warm fire, a coat of paint, cooking, cleaning supplies or a variety of other products and activities, VOCs are a common fixture in a home and repeated exposure and trigger serious damage, not just to lungs, but to the heart, liver and kidneys as well.
The way most consumer-grade air purifiers deal with these issues is by use of a filter to physically trap VOCs. However, some products (such as the products that were the subject of the MIT study) claim to offer protection through oxidation or ionization that help break down VOCs instead.
As professor of civil and environmental engineering and chemical engineering Jesse Kroll, explains, “Oxidation of VOCs is what leads to a lot of important pollutants in our atmosphere, such as ground-level ozone or secondary fine particulate matter. So there’s this concern in the atmospheric chemistry community that maybe some of these cleaners that claim to be oxidizing away the VOCs are actually generating these harmful byproducts.”
The other large concern with the products, according to the researchers, is that they simply aren’t regulated. Very little data often exists to specify the VOC removal rates, and, as evidenced by the study, they often end up creating more VOCs through their reactions.
Instead, Kroll is willing to advocate some better solutions. “Air cleaning using activated carbon filters, a tried-and-true technology that doesn’t rely on chemical reactions, is still the way to go.”