Key points to remember
- Good air circulation can help reduce transmission of COVID-19 indoors, even if mask mandates go away.
- Air filters can again protect against all three types of COVID transmission: inhalation, deposition and touch.
- Research shows that adding portable air purifiers to spaces that already have HVAC systems can dramatically improve airflow.
Mask mandates are gradually disappearing. This leaves many people wondering if improved ventilation strategies in indoor public spaces help reduce the transmission of COVID-19.
Experts say yes. Better ventilation helps and is crucial for the future, especially as fewer people wear masks.
“It’s not an airtight guarantee that you won’t get COVID,” said Andrew Noymer, PhD, MSc, epidemiologist and associate professor of population health and disease prevention at the University of California at Irvine, at Verywell. “It’s just a very small probability because the air isn’t as stale.”
Why good ventilation is crucial
Last month, a federal judge overturned the Centers for Disease Control and Prevention (CDC) mask mandate for planes, trains and buses. Some carriers still have their own mandates and some cities still have mask rules that are also in effect for local transit. But much of the nation is now without a mandate.
Experts say research shows improved indoor ventilation through filters and portable air purifiers can help reduce transmission of the virus in indoor public spaces. Additionally, people can also take steps to improve and monitor ventilation in private spaces, especially when planning to host guests.
The virus that causes COVID-19 spreads in three ways: inhalation, deposition and contact, according to the CDC. The virus is released as tiny droplets or aerosols when an infected person exhales, speaks, coughs or sneezes. Transmission mainly occurs when another person inhales the infected aerosols.
Infected aerosols can also be deposited from the air directly onto mucous membranes, such as the eyes, nose or mouth. And aerosols can also contaminate the surfaces we touch. Although surface transmission is unlikely, it is possible for us to become infected if we transfer the virus to a mucous membrane.
“When you’re in a climate-controlled indoor building, those little droplets can just float around in air currents for minutes,” Noymer said.
However, if air is passed through the filter of a ventilation system several times per hour, it can help reduce transmission. Indeed, a good filter will trap the aerosols, preventing them from recirculating. But not all ventilation strategies, systems, and filters are created equal.
The Environmental Protection Agency (EPA) recommends that building operators upgrade their filters to the highest efficiency compatible with the building’s HVAC system and use portable air purifiers to improve overall circulation to reduce viral transmission.
Portable air purifiers improve ventilation
In a recent study, researchers from the Well Living Lab, a collaboration between the Mayo Clinic and Delos, simulated a classroom environment. They strategically placed three recirculating portable air filtration units around the room, which was also equipped with HVAC.
The researchers then used colored particles and a breathing simulator to test the dispersion and deposition of the aerosols. They tested conditions with only the HVAC unit running and with the HVAC running in tandem with the portable units.
“What we found was that using these portable air-purifying units really did reduce the concentration of particulate matter by up to five times,” said Zachary Pope, PhD, MS, researcher and author of the study, at Verywell. “So obviously having that reduction in the amount of particles in the air is good because you theoretically don’t have as many potentially infectious particles in the air.”
In their simulation, the researchers also placed objects commonly used in a classroom, such as desks, a whiteboard, digital tablets, etc., all surfaces likely to be contaminated.
“Our study was able to help show that cleaning portable air — because it reduces the amount of particles in the air — also reduces the amount of particles that settle on surfaces,” Pope said. “And those two factors really help us limit both direct inhalation transmission and transmission through different surfaces in a room.”
Although the study tested a fictional classroom, Pope says portable air purifiers are useful for other environments, such as offices, cubicles, homes, and more. “They’re very profitable and they have a lot of impact,” he said.
The use of portable air purifiers is especially important in buildings where ventilation systems cannot be upgraded. And even where HVAC systems can be improved, portable units still improve airflow and help purify the air.
Buy a portable air purifier
If you’re buying a portable air purifier, Pope recommends first knowing the dimensions of your space. Next, check the cubic feet per minute (CFM) rating specifications of the air purifier.
“Ideally what you want is for that CFM to be at least two-thirds the square footage of your room,” he said. For example, a unit with a 100 CFM rating can adequately ventilate 150 square feet. If you have a larger room, you may need two or more units.
If you need an even more economical option, Noymer says there’s what he calls a “hack” if you make a Corsi-Rosenthal Box. The method is to use a box fan and HVAC filters.
“It’s basically a DIY,” he said.
A study conducted by researchers at the University of California, Davis shows that the Corsi-Rosenthal box reduces the concentration of particles. The study is available as a preprint and has not yet been peer-reviewed.
The university offers instructions for making a Corsi-Rosenthal box on its website.
What about opening Windows?
Opening windows can also significantly improve ventilation.
“In summer or wherever possible and practical [opening windows] is something I highly recommend,” Noymer said.
Sometimes that’s not always feasible, adds Pope, as in the case of skyscrapers. And opening windows may not be ideal or advisable when the air quality or the weather is poor, such as during wildfires, high pollen counts or storms.
One way to monitor if the air is stale in a space is to use a carbon dioxide meter, which can be purchased online, Noymer said.
“CO2 is an indirect measure of the quality of the airflow in the room,” he explains. “If CO2 continues to rise, it’s not circulating very well. And if CO2 stays at relatively low levels, then it’s circulating very well.”
A CO2 meter can be a useful tool if you are hosting a private indoor event this summer, for example. A rising level may prompt you to open an additional window.
Ultimately, improving ventilation will remain a vital strategy to reduce viral transmission in the future as we move forward into year three of the COVID-19 pandemic and beyond.
“It needs to be part of public health and safety codes,” Noymer said. “In the long term, we need to rethink the air in public spaces.”
What this means for you
While masks provide significant protection against COVID-19 transmission, high-efficiency HVAC systems can further reduce your risk in places ranging from offices to airplanes. Not sure what the HVAC situation is in your office? Bringing a portable air purifier is also helpful.
The information in this article is current as of the date indicated, which means that more recent information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.