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What Does an Air Purifier Do?

What does an air purifier do - featured. Large air purifier stands in living room, near the sofa, a house plant and a resting cat

We spoke to an indoor air quality researcher to find out how to make your home a haven of fresh air

We come into our homes at the end of the day and believe we’ve closed the door on the pollutants and dirt outside. However, scientists are now categorical that this isn’t the case.

The Environmental Protection Agency states that Americans spend on average approximately 90% of their time indoors, and concentrations of some pollutants inside are often two to five times higher than those outdoors. This can be anything from animal dander, pollen, and dust mites to smoke from cooking.

Marina Eller Vance, an assistant professor of mechanical engineering at the University of Colorado Boulder, was one of 60 scientists who used $4.5m worth of high-tech instrumentation in what The New Yorker described as “a four-week orgy of cooking, cleaning and emissions measurement.”

As the team prepared the second of two mock Thanksgiving meals, measuring the fine particulate concentration in the air, they were shocked to discover that, as the stuffing and pies came out of the oven, the fine particulate matter in the air was within the range that the Environmental Protection Agency’s Air Quality Index defines as “very unhealthy”.

Vance says: “We tend to believe that our indoor air is cleaner than outdoor air – which it usually is, at least in most major cities and most places near traffic. But outdoor air pollution can penetrate indoors and affect our homes”. She adds: “There are also situations where the outdoor air can be clean but our indoor activities can make air quality inside worse, at least temporarily. Things such as cooking and any kind of combustion (smoking, burning incense or candles, for instance) can emit indoor air pollutants.”

This is the reason to consider an air purifier, which can improve your indoor air quality – especially, says Vance, if you live in an area of high traffic, industry or even wildfires. “Another application might be to remove air pollutants from some indoor sources, such as particles from cooking or other combustion processes”, she says. An extractor hood is a good option for this. However, remember that an air purifier will not remove particles embedded in furniture or those that have settled on surfaces.

What does an air purifier do?

Air purifiers are designed to filter particulate matter, which includes animal dander, pollen and volatile organic compounds (VOCs) that can come from cooking or even from mothballs.

Built around filters – which tend to be made of paper, fiber (often fiberglass) threads or mesh – air purifiers pull in your atmospheric air, filter it, and then release the cleaned air back into the room. The most common are HEPA filters for allergens such as pollen and other air pollutants; but these will also be useful if you live in an area susceptible to wildfires. There are models that may also come with an activated carbon filter, which will absorb VOCs and some odors, too.

Certain models of air purifier may also include a preliminary filter, which extracts larger pollutant particles including lint, pet dander, hair and dust, while those that include ultraviolet light filters even claim to destroy biological nasties such as mold or bacteria.

Note that in all instances filters will need to be replaced – and this will vary from one model to the next. Carbon filters, for example, will need to be switched out as often as every three months. Some models arrive with reusable and washable filters.

Models arrive in all shapes and sizes, with some including displays that show air quality while others even include smart features and link to your cell phone for real-time updates and control.

How to pick an air purifier

“As an indoor air quality researcher, I’d choose an air purifier that includes a high-quality filter (such as HEPA) and is appropriately sized for the space where it will be used”, Vance explains. “In order to size your air purifier properly, you should consider its clean air delivery rate (CADR) and use the ‘2/3 rule’: the air cleaner should have a CADR that’s at least 2/3 of the square footage of the space”, she continues.

What does an air purifier do. Two pleated carbon filters on a white background, one in the center and one in the corner of the image

“Some air cleaners also have an activated carbon layer, which can be helpful to remove odors and some gases, but while the particle filter will remain effective for long periods of time, the activated carbon filter may require replacing more frequently.” In most cases, Vance believes that a good quality filter may be all you need in an air cleaner.

Other things to consider are noise – check for a night time mode, for example, to avoid being disturbed if the air purifier is being run while you sleep – and running costs. Regarding the latter, in order to be effective, you’ll need to run an air purifier pretty much constantly in order to keep the air circulating, which means considering electricity and the cost of replacing filters. It might also be an idea to check whether a device has Association of Home Appliance Manufacturers’ certification (AHAM).

The AHAM Verifide mark is used to denote that an air cleaner has been tested using a standardized method outlined by AHAM. It provides another level of reassurance and trust that the air cleaner you are buying does what it claims, particularly in delivering those CADR levels.

There are a host of government and health organisations offering free guidance on air purifiers. Do your research, and you’ll be sure to find the perfect air purifier for your home.

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