Over the past 11 months, there has been a constant flow of new developments regarding COVID-19 seemingly every day. It can be overwhelming trying to keep up with the latest news as new research is published every week. In today’s blog, I am going to discuss if air cleaners can be an effective way to improve COVID air quality.
COVID Air Quality – The Basics
The SARS-CoV 2 virus is very very small, however, it does not float around “naked”. The COVID virus is within respiratory droplets that are released when a person coughs, sneezes, or speaks. These droplets are made up of water, mucus, other bodily proteins, as well as microbes like viruses and bacteria. The size of these droplets can vary, typically can be found anywhere in the range of 0.05 to 500 micrometers (μm). The smallest of these droplets are frequently called “aerosols”. The question remains if you can filter these droplets and aerosols from the air, does that improve COVID air quality and lower the risk of transmission?
Combating Droplets and Aerosols
The best tool we have to address airborne droplets and aerosols is HEPA filtration. HEPA filtration is a rating for particulate filters that have been documented to filter out 99.97% of particles sized 0.3 μm in diameter. For the rating, 0.3 μm is selected as the qualification size because it is very close to the most penetrating particle size (MPPS). The MPPS is the aerodynamic particle size that is most difficult to filter. Counterintuitively, it is easier to filter out particles smaller than the MPPS, so HEPA filters can be effective to filter out particles of any size, large or very small.
The EPA and CDC agree that HEPA air cleaners are not enough to completely protect people from exposure to the virus in indoor settings, but can be used in tandem with other best practices in a comprehensive plan to reduce transmission of COVID indoors.
The research shows that the best mitigation method to reduce airborne COVID transmission is to improve ventilation. In a home, this could mean cracking a few windows or operating an outdoor air intake on your HVAC. Opening a window only a few inches can in some cases be enough to increase air exchange to a level that drastically reduces the risk of COVID transmission. In commercial settings, many large buildings have adjusted the amount of fresh air they are bringing into a building, even in the cooler months when outdoor air intakes are normally only letting a very small amount of outdoor air into the building to try to conserve energy. Ventilation, not filtration, is the closest we have to a “silver bullet” in improving COVID air quality, but it is not perfect and should also be used together with a more comprehensive plan.
A Multi-Level Approach to COVID Air Quality
When ventilation is tricky, air cleaners can help supplement. For example, a home without mechanical ventilation may not be able to open up windows on a freezing cold day. If someone is coming over, a portable air cleaner would be helpful. Or perhaps a particular office in a commercial building doesn’t get sufficient outdoor air ventilation from the HVAC system and it has no operable window. If people will be meeting in that private office, a portable air cleaner would also be helpful.
Although ventilation and air cleaners can improve COVID air quality, they are not enough to stop transmission rates indoors. We need different mitigation measures for the other modes of disease transmission: fomite (surfaces) and droplet spray (direct sneeze). For these other transmission modes, mitigation measures such as social distancing, mask-wearing, and hand washing are needed. In a future blog, we will discuss how to select an air cleaner.