By now, we all know the effect secondary cigarette smoke can have on our lungs, which has led to a big clampdown against public smoking around the world. Similarly, society is getting increasing concerned about the effect of traffic pollution on our health, especially in inner cities. But ultimately, we spend far more time in our homes than in public spaces. So it makes sense to focus on having clean air quality there, too.
After all, our front doors are not magical barriers that keep pollutants and allergens out of our living space. Even if they were, we also generate pollutants within our homes ourselves, from things like cooking, cleaning, building materials, products and furniture.
Indoor air pollutants come in the form of tiny particles, such as PM2.5 and PM10, formaldehyde, mold and pollen. They may also appear as gases, such as volatile organic compounds (VOCs). So reducing them in the air we breathe makes sense. Which is why the best air purifiers are increasingly popular.
But how do air purifiers work, and are they truly effective? Read on as we answer these questions, and explain how to find the right product for you.
How do air purifiers work?
The basic principle behind air purifiers is pretty straightforward. They suck in air from their surroundings, pass it through one or more filters to remove pollutants, and then release the cleaned air back into the room. That's it.
There are a number of different types of filters they use, but the most common (and most effective) is the High-Efficiency Particulate Air (HEPA) filter. These filters are designed to trap 99.97% of particles that are 0.3 microns in diameter or larger. To give you a sense of scale, a human hair is typically 50-70 microns in diameter. So we're talking about very tiny particles here indeed.
The effectiveness of a HEPA filter is usually expressed as a MERV rating (which stands for Minimum Efficiency Reporting Values). They generally range from 12 to 17, and your air purifier needs to have a MERV rating of at least 13 to be worth using.
Do air purifiers work?
The million dollar question is: do air purifiers actually work? The answer is yes, in some circumstances. According to the Environmental Protection Agency: "Some air cleaners, under the right conditions, can effectively remove certain respirable-size particles."
When equipped with activated carbon filters, some air purifiers have also found to be effective in reducing volatile organic compounds (VOCs). That said, according to this 2021 MIT study, models vary in effectiveness, and some were even found to be be a source of VOCs themselves.
The short version, then, is that air purifiers do usually work... but how well they work depends on a number of factors. These include the specific product in question, the type of purifier, the size of the room, the specific air quality issues in a particular building, the level of ventilation in your home, the size of the space, how consistently you use the air purifier, and how often you change the filters.
Even in the best case scenario, though, air purifiers are not a cure-all for indoor air quality issues. Firstly, they cannot remove all pollutants, particularly those that have settled on surfaces. And secondly, they're most effective when used in conjunction with other air quality improvement measures, such as regular cleaning and proper ventilation.
The University of Massachusetts puts it plainly in this report: "Using a portable air cleaner is the least effective way to clean the air, but it can be a good supplement to ventilation." In other words, if you use an air purifier, but rarely open your windows or clean your home, don't be surprised if you still get sick.
How to choose an air purifier
When shopping for an air purifier, there are several key factors to consider:
The first is CADR (Clean Air Delivery Rate). This is a measure of how quickly the purifier can clean the air in a given room size. Look for a CADR that's at least two-thirds of the room's area in square feet. For example, for a 300 square foot room, you'd want a CADR of at least 200.
Secondly, think about your room size. Manufacturers typically list the maximum room size for which an air purifier is effective, so make sure you check this before buying
Thirdly, pay attention to filter type. As we mentioned earlier, HEPA filters are the gold standard for particle removal. Look for 'True HEPA' filters, which meet the US Department of Energy's standards. Some models also include additional filters, such as activated carbon filters (for removing odors and some gases) or UV-C light filters, which can kill some bacteria and viruses, although they won't remove particles.
Fourthly, consider how much you value peace and quiet, as air purifiers can produce noise, especially at higher fan speeds. If this is a concern, check the decibel rating before you buy.
Finally, consider whether you need added features. Some air purifiers come with cool extras such as air quality sensors, automatic mode, and smartphone connectivity, although these will usually be reflected in a higher overall price.
