An inexpensive, easy-to-construct air filter was demonstrated by researchers from Silent Spring Institute, Massachusetts, and Brown University to effectively reduce the indoor air concentrations of many semi-volatile organic compounds.

Initially deployed to stem the transmission of COVID-19, Corsi-Rosenthal boxes were constructed from materials found at hardware stores: four MERV-13 filters, duct tape, a 20-inch box fan and a cardboard box. As part of a school-wide project, these devices were assembled by students and campus community members and installed in the School of Public Health as well as other buildings on the Brown University campus.

As reported in Environmental Science & Technology, the boxes significantly decreased the concentrations of several per- and polyfluoroalkyl substances (PFAS) and phthalates in 17 rooms at the School of Public Health during a two-month test period. PFAS levels decreased by 40% to 60%, and concentrations of phthalates were reduced by 30% to 60%.

However, the Corsi-Rosenthal boxes were discovered to have an audio side effect: they increased sound levels by an average of 5 decibels during the day and 10 decibels at night, which could be considered distracting in certain settings, such as classrooms. According to the researchers, the health benefits of the box in reducing indoor air pollutant levels likely outweigh the noisy side effects.