UA researchers build DIY air purifiers to remove COVID particles

University of Arkansas researcher and physics professor Hugh Churchill is creating and testing portable air filters that help remove infectious airborne particles — including respiratory droplets that carry coronavirus — from interior environments using simple, inexpensive supplies available at any general department or home improvement store.

And he wants to teach you how to make your own. Duct tape, a basic box fan and commercially available air filters are all you’ll need.

“While masks and vaccines are polarizing topics, there shouldn’t be anything controversial about clean air,” Churchill said in a UA news release. “These devices facilitate that. They provide an additional layer of protection that could be widely deployed to make our K-12 and university indoor spaces healthier during this wave of the pandemic. And they’re easy and inexpensive to build. My 9-year-old built one.”

Churchill, who heads up an experimental research group in the physics department, researches condensed matter and quantum materials to develop or improve gadgets that benefit people and the environment. According to the UA, his lab, for example, focuses on spiraling chains of selenium and tellurium. When employed in nanowires, these two minerals show promise in the next generation of digital technology, solar energy and quantum computing.

But, for the time being, this and other projects have taken a back seat to the struggle against COVID-19. Churchill has been working with the UA’s facilities management division and the Arkansas Research Alliance for several weeks to create and test a prototype of a basic box-fan filter that helps purify indoor air.

“Improving filtration and ventilation in classrooms is a common recommendation to help fight the spread of COVID-19 and improve indoor air quality,” Churchill said. “There are commercial products that do this, but they can be cost-prohibitive. Our teachers and school districts have worked extremely hard and used many tools to keep our kids’ classrooms safe. This is one more tool to help them.”

HOW IT WORKS
According to the UA, there is a growing trend in the facilities and HVAC communities around the country to make indoor places as safe as possible. Citizen scientists and amateurs have joined the effort, creating homemade air purifiers based on open-source and simple do-it-yourself designs by air-quality specialists.

Churchill gives the manufacture and testing of a homemade box-fan filter a higher level of scientific credibility. He spends a lot of time working on nanoscale electrical devices, and one of his primary goals is to eliminate air particles, which can damage them. Churchill has also spent 15 years working in so-called “clean rooms” with highly well-filtered air.

A particle counter, which Churchill uses in his lab to analyze different filters, is used to monitor the purifier’s success. They also use sophisticated microscopes to see microscopic pores in the filter material, holes through which particles can pass. One of the filters they tested from a well-known company, for example, had numerous such holes. As a result, its particle removal effectiveness was found to be significantly lower than anticipated.

According to the UA, Churchill’s purifier is an improved version of Richard Corsi’s “Corsi-Rosenthal cube,” conceived and designed at Portland State University. Corsi is a well-known expert in the field of indoor air quality. The sides of the cube are made up of four or five filters with a minimum efficiency reporting value of 13 (known as “MERV” in the HVAC sector) and a simple fan. Duct tape is used to seal and hold the corners and seams together. When numerous filters are used, the rate of clean air distribution is increased, and the cube lasts longer, maybe six months.

Churchill tested the particle filtering effectiveness and airflow of the filters with the help of UA facilities management HVAC expert Ben Doudna. The cubes can deliver an estimated 470 cubic feet per minute of clean air, which means one cube could produce four air changes per hour for a 900-square-foot classroom with 8-foot ceilings. That falls within the recommended range of four to six air changes per hour for preventing airborne transmission.

THE SCIENCE BEHIND AIR FILTERS
The best strategies to prevent the spread of coronavirus include vaccinations and wearing a mask. That is especially crucial in high-risk environments like health clinics, vaccination and medical testing sites, and schools, where nearly half of the population is still unvaccinated. Still, the Centers for Disease Control and Prevention also suggests using portable air filters to eliminate infectious airborne particles from interior spaces.

SARS-CoV-2, the virus that produces COVID-19, has a particle size of roughly 0.1 micrometers, or one-tenth of a micrometer. One micrometer is 100 times smaller than the thickness of a sheet of paper to give an idea of how little that is. When virus particles are expelled via talking, singing, breathing, or coughing, they become trapped in larger particles, some of which rapidly drop out of the air, and others linger in room air for minutes to hours.

High-efficiency particulate air (HEPA) filters, according to the CDC, capture 99.97% of human-generated virus particles linked with SARS-CoV-2. Portable filtration systems with a HEPA filter and a motorized fan system do not bring in outside air for dilution. Still, they can clean the air within a space to lower the concentration of airborne particles.

The cost of a commercial HEPA-based fan is around $250. A box fan, four filters, and duct tape, according to Churchill, would cost less than $100. For half the price, a single-filter design ideal for smaller rooms can also be made. He underlined that the U.S. Department of Education has confirmed that the American Rescue Plan can cover costs for air-quality upgrades in elementary, secondary, and higher education classrooms.

COLLABORATION
Churchill is an Arkansas Research Alliance Academy fellow. The ARA Academy comprises 32 strategic research leaders from five institutions, as well as the state’s only national lab. Churchill collaborates with Douglas Hutchings, director of the ARA Academy, to provide web-based tools that explain the purifier’s science and offer directions to manufacturing them.

These tools are available at CleanARAir, where Churchill and Hutchings also link Walmart.com and Amazon shopping carts where instructors and parents can purchase parts and kits. The site provides information on the effectiveness of filters.

Churchill and Hutchings have created instructional materials about the purifier’s design and operation. Lesson plans in math, physics, and English/language arts, ranging from fundamental literacy to advanced calculus, are also available at CleanARAir. For example, there are various possibilities to quantify flow rates, particle counts, and proportional connections for the math and scientific components of the project. Students can also try out a variety of different designs. Students can use curriculum kits to create hypotheses and test them quickly to compare modeled data to measurement data.

Innovate Arkansas, a state-sponsored initiative that assists technology entrepreneurs in forming sustainable businesses, has aided in developing the supply chain required to distribute thousands of kits. The Northwest Arkansas Council organizes negotiations with area business and charity leaders to offer wholesale prices and swiftly distribute kits to instructors.

Startup Junkie, a nonprofit that provides coaching services to entrepreneurs, has also assisted the researchers in developing a method to receive tax-deductible donations to help get purifiers into the hands of teachers and schools.