How does an air purifier work?

Good question. Just how the heck does an air purifier work?? Of course, it all depends on the technology involved. Sound complicated? Not really, but it's worth a closer look.

Welcome to Air Purifier 101

... So, everyone in the right place?

Good. Everyone take notes. There will be a quiz. Ready? Here we go:

Air purifiers draw air from a room, clean it, and return the air to the room.

Ok, class dismissed. Pick up a diploma on the way out.

What's that? Looking for more?

Ok, Ok! But let's set some ground rules first.

Two things to keep in mind:

• There is no single, cure-all air purifier. That is one of the reasons there are so many different brands and technologies in play. That is why education is so important.

• Within each type of air purifier, there are those who do it well and those who don't. Yeah, a real shocker.

Before we can answer the question, "How does an air purifier work?" we need to set up some categories.

Broadly speaking, the best air purifiers can be broken down this way:

Mechanical filtration
These rely on physical, paper filters to "strain" particles out of the air. These are called HEPA Air Purifiers.

Ionic filtration
These give airborne particles a positive or negative charge, after which they are attracted to walls, furniture or anything else with an opposite charge.

Electrostatic filtration
These are ion systems that have charged collection plates that catch the particles rather than releasing them into the room.

Charged filter filtration
More or less what it sounds like: Particles are charged, but mechanically filtered out of the air.

Ozone generators
These change the chemical composition of particles. Used in some industrial settings, controversial for home use.

Also, there are at least two popular accessories:

• All forms of purifiers can include UV systems designed to kill bacteria, virus and other organic materials.
• Many systems can include carbon filters to reduce odors.
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So let's get down to it. How does an air purifier work?

Mechanical air purifiers for your home

Mechanical filtration is the oldest, most obvious form of air purifiers for your home.

It's like most other filtration systems you've ever heard of, from your furnace filter to the air filter on your car. Along with ionic air purifiers for your home, it's one of the most popular air cleaners.

In the case of an air filter, a fan draws the air into the room through a paper screen, or filter. The screen is, of course, very fine.

Many such systems may use more than one filter (for example, a pre-filter to strain out larger particles and a carbon filter to reduce odors).

The main filter in any of the mechanical air purifiers for your home is called a HEPA filter, a very fine filter that removes particles down to O.3 microns.

Advantages

A solid technology that has been around for a loooong time, it has several things going for it.

Most importantly, the filter doesn't lose efficiency very quickly.

Paradoxally, it becomes even more efficient over time as it picks up pollutants, causing the paper filter to become even more fine.

The problem, of course, is the more dirty a filter is, the harder it gets to pull air through it. That means the motor works harder, uses more electricity, and sounds louder with more wear and tear, all to move the same amount of air - or even less!

So you must regularly change filters or less air is cleaned regularly, not to mention the strain on the fan and motor.

Disadvantages

Two biggies for many, one which we touched on above:

• It needs a good fan to pull air through the filter(s), which means all mechanical purifiers have some fan noise.

Different makes and models do a better job masking it. Fan noise can be a funny thing. Many people actually prefer the smooth, consistent background sound a small fan adds.

But an uneven, warbly sound will drive anyone nuts.

And secondly,

• Filters must be periodically changed.

This is a small, added expense in time and money worth noting.

The length of time a filter will last varies greatly depending on the model and use of air purifiers for your home.

In general, plan for anywhere from six months to two years.

Ionic air cleaners

A popular alternative to mechanical purifiers, the ionic air cleaners are also the basis for electrostatic and charged filter purifiers.

Here's how it works.

These small devices ionize particles as they move through it, giving them an electrical charge.

The charged particles are then sent back into the room where they are attracted to walls, furniture or anything oppositely charged.

The net result is particles are removed from the air, though not from the room.

Advantages of ionic air purifiers

• Quiet: They usually have very small, low-speed fans that are essentially silent.
• No filters to change or clean: Pretty much zero maintenance machines.
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Disadvantages of ionic air purifiers

• The biggie: Particles are not actually removed from circulation.

The charged particles can easily be stirred back up into the air by movements in the room: doors opening and closing, animals and kids, etc.

Some worry that when ingested, the charged particles are more likely to attach themselves to the walls of the lungs, making them more of a health risk.

A few other concerns about ionic air cleaners:

• Black walls: Surfaces near the purifier are prone to be covered in particles and must be regularly vacuumed clean.

• Health questions: The ALA has stated that ionized particles may be more likely to stay in the lungs, attaching themselves to the lungs just as they would to the walls of your room.

• Not much air flow: If an ionic air purifier has no fan, it will not be able to circulate enough air to be effective. But even with a small fan, these units are typically best for small areas where there is limited foot traffic.

• Ozone: Ozone is produced as a byproduct when high voltage near the charging wires converts oxygen to ozone, which then exits the machine and flows into the room air.

By far the most controversial of air purifiers for home use is the ozone machine.

Here's how it works.

The machine pumps ozone into the room which reacts with gas and chemicals in the air, changing the chemical composition of these elements.

It is among the most popular for industrial uses (ie, hotels often use them to clear smoke and other smells from hotel rooms in between guests).

Advantages of the ozone generator

• No filters to clean
• Good for odors

As stated above, hotels often put them in a room on high with doors and windows closed.

Later, the windows and doors are opened to air out the ozone before the room is reused.

Disadvantages of the ozone machine

There are plenty, but here are the most often cited:

• Concentrated doses of ozone are considered a health risk. Manufacturers of these machines say the concentrations aren't dangerous. Third party testing by Consumer Reports and others consistently cite dangerous levels of ozone.

• An irritant: Ozone can aggravate allergies, especially for those who already have asthma or other acute allergies.

• Particles remain: No filters, no ionized particles - no real effect on particles in the air. Its impact is on gases and odors in the air.

What most do agree on: It is the best of the odor-eliminating air purifiers.


There are, of course, all kinds of add-ons and options that you will find with any home air filter.

Here are two of the more substantial and popular accessories for air purifiers:

• All forms of purifiers can include UV systems designed to kill bacteria, virus and other organic materials.

• Mechanical filtration systems can include carbon filters to reduce odors.

These are options that are generally used in conjunction with other technologies.

Carbon filter

How it works:

Active carbon filters physically absorb gas molecules into their pores.

They are often referred to as gas filters and can be found in air purifiers of almost any technology.

Keep in mind:

While these gas filters remove many gases and odors and some part of smoke, they will little or no impact on particles in the air. In a typical home air purifier, they are accompanied by a HEPA filter to strain out airborne particles.

U.V. system

How it works:

Ultraviolet light is used to sterilized microorganisms in the air, such as molds, bacteria and viruses.

Keep in mind:

UV is only effective when the microorganisms are expected to get a high enough dosage over an extended period of time.

Lower fan speeds will be more efficient, but that means the amount of air cleaned by the purifier is generally limited.

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