DIY filter can help to clear the air

As acrid wildfire smoke from Quebec and northeastern Ontario drifted to the GTA this week, Kristin Iorio, who lives with asthma, could feel her chest constrict and her breathing become heavier.

So, she decided to build an air purifier herself in order to clean the air in her home in Ajax. Using nothing more than two air filters, a portable fan, some duct tape and cardboard, Iorio was able to assemble a makeshift purifier in less than 30 minutes. After turning it on, the impact was noticeable.

“I can just say anecdotally, I coughed and wheezed less,” Iorio said. “It’s certainly worth the effort to build it.”

These DIY air purifiers were popularized during the COVID-19 pandemic, when people sought to mitigate COVID-19 transmission in indoor settings. Now, however, as wildfire smoke envelops large swaths of southern Ontario and the U.S. eastern seaboard, the devices have been thrust in the spotlight once again.

Iorio, a chemical engineering PhD student at the University of Toronto studying air quality, said these homemade purifiers are a simple and effective tool to improve air quality and remove pollutants.

“It doesn’t need to be pretty to work,” she said.

The efficiency of these DIY devices vary based on, among various factors, the type of fan and filters used, along with the size of the room. Iorio’s improvised purifier reduced the particle concentration inside the house by about 70 per cent after about 30 minutes, she said after measuring it with her particle monitor.

Perhaps the most well-known version of the DIY air purifier is the Corsi-Rosenthal box, cocreated during the pandemic by environmental engineer Richard Corsi and filter manufacturer Jim Rosenthal.

Informal tests found the device removed about 60 per cent of onemicron particles out of the air, and nearly 90 per cent of the 10-micron ones. For context, much of the air pollution produced by the forest fires are 2.5 microns or smaller.

To build the Corsi-Rosenthal box, here’s what you need: a box fan, the cardboard box for the fan, duct tape and four filters with a MERV (minimum efficiency reporting value) rating of 13 or higher.

First, build the four vertical walls of the DIY purifier using the four air filters, connecting them together using duct tape. Ensure the seals between the filters are air tight, as you want all the air flowing into the fan to pass through the filters.

Next, place the filters on the floor, on top of the cardboard box which contained the fan. Again, tape all four edges to create an airtight seal.

Finally, install the box fan at the top of the contraption and tape the corners to the filters.

While the device is safe to use — tests have shown it is very unlikely to cause a fire — Iorio recommends checking on the device regularly while in use to ensure the fan does not overheat.

Iorio’s indoor particle concentration was roughly one-third of the outdoor concentration before she turned on the filter’s fan at around 10 a.m. — but noted this measurement will vary from house to house.

Within the first 15 minutes of the fan being on, the particle concentration dropped by 67 per cent.

Nearly an hour later, it dropped to the background concentration of her house — the levels they’re usually at without wildfire smoke.