With concerns about respiratory illnesses like COVID-19, many have turned their attention to indoor air quality. A common question is whether an air purifier can reduce the risk of viral spread in homes and offices. These devices filter contaminants, but their effectiveness against viruses depends on their technology and proper use.
How Air Purifiers Target Airborne Viruses
When an individual with a respiratory infection like COVID-19 breathes or coughs, they release virus-laden particles called respiratory aerosols. These particles can remain suspended in the air for extended periods, posing a risk to others. This airborne route is a recognized mode of transmission for the virus.
Air purifiers work by drawing a room’s air through filters. The primary mechanism for capturing viruses is mechanical filtration. While the SARS-CoV-2 virus is small, at about 0.1 microns, it travels embedded within larger respiratory droplets and aerosols, which are easier to capture.
These virus-carrying particles fall well within the capture range of high-efficiency filters. The filter’s dense mat of fibers traps these particles as air passes through. Due to physical principles like Brownian motion, filters can also capture particles smaller than their rated size as they move randomly and collide with the fibers.
Key Features for Selecting an Air Purifier
The most important feature to consider is the filter type. High-Efficiency Particulate Air (HEPA) filters are the standard for effective air cleaning. A “True HEPA” filter is certified to capture 99.97% of airborne particles down to 0.3 microns. This size is used for testing because it is difficult to trap, meaning the filter is also efficient at capturing both larger and smaller particles.
Another specification is the Clean Air Delivery Rate (CADR). Measured in cubic feet per minute (CFM), this metric indicates how quickly the purifier can clean a particular room size. For effectiveness against virus-carrying particles, the smoke rating is the most relevant due to the small size of smoke particles.
To select a purifier, match its CADR to your room’s square footage. A guideline is that the CADR number should be at least two-thirds of the room’s area in square feet. For instance, a 150-square-foot room benefits from a purifier with a CADR of at least 100. This ensures the unit can perform five or more air changes per hour (ACH) for effective particle removal.
Some purifiers use technologies like UV-C light or ionizers, but these have caveats. UV-C light requires sufficient exposure time to inactivate viruses, which may not be achieved in a fast-moving airstream. Some electronic purifiers, including certain ionizers, can produce ozone as a byproduct, and the EPA warns against using purifiers that generate this lung irritant.
Proper Use and Placement for Maximum Effect
A purifier’s effectiveness is heavily dependent on proper placement. To function optimally, the unit must circulate air freely. Placing a purifier in a corner, behind furniture, or against a wall will obstruct airflow and reduce its ability to clean the room. It should be positioned in an open area to create an effective air circulation pattern.
For the purifier to have a meaningful impact on airborne particle concentration, it needs to be running continuously while the space is occupied. Turning the unit on only intermittently allows contaminant levels to build back up. Running it on the highest fan speed that is comfortable will maximize the CADR and provide the most robust air cleaning, increasing the number of times the room’s entire volume of air passes through the filter each hour.
Regular maintenance is also a necessity for sustained performance. Over time, the filter will become loaded with captured pollutants, which restricts airflow and reduces the unit’s efficiency. It is important to follow the manufacturer’s recommendations for filter replacement. A clogged filter cannot do its job properly, and failing to change it essentially renders the device ineffective.
Role in a Layered Protection Strategy
It is important to understand that an air purifier is not a standalone solution that guarantees protection from COVID-19. Instead, it should be viewed as one component within a multi-layered approach to reducing transmission risk. Air purification acts as a supplement to more fundamental public health measures, not a replacement for them.
The effectiveness of an air purifier is greatly enhanced when used in conjunction with good ventilation. Diluting indoor air by opening windows and doors to bring in fresh outdoor air is a primary strategy for lowering the concentration of all indoor pollutants, including viral aerosols. When outdoor ventilation is not possible or sufficient, an air purifier provides an additional layer of risk reduction by actively removing particles from the air that remains.
Using an air purifier does not eliminate the value of other personal protective measures. In situations with elevated risk, practices like wearing a high-quality mask and maintaining physical distance remain important tools for preventing transmission. An air purifier helps clean the shared air in a space, but it does not stop close-range transmission from direct respiratory droplets. Combining air purification with ventilation and other safety protocols creates a more resilient defense against viral spread.