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How Air Purifiers Work?

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How home air purifiers work

Air purifiers draw air into its chamber, purifies it, and expels cleaned air back into a room.  The idea is to remove contaminants like pollen, dust, pet dander, smoke, mold spores, bacteria, and viruses.  However, the effectiveness depends on the method and the contaminant itself.


Currently, there are five types of air purifiers.

HEPA (High Efficiency Particulate Air) Purifiers

These use HEPA filters that allow less than 0.03% of particles as small as 0.3 micrometers to pass through them.  They trap larger particles in the filter.  This is the only filter that meets the U.S. Department of Energy’s standard for air particle removal.

Adsorbent Purifiers

These use the surface of a porous substance to trap passing molecules.  Activated charcoal is commonly used as a filtrate.

Ultraviolet (UV) Purifiers

As air passes through the purifier, a UV light sterilizes bacteria and viruses.

Ionization Purifiers

A method called a corona discharge (remember physics class) creates positively and negatively charged molecules called ions .  A negatively charged metal plate and a positively charged metal plate in the purifier will attract particles in the air.  Depending on whether the molecule in the air is positively or negatively charged, it will gravitate to the oppositely charged plate to neutralize its charge.

Ozone-Generating Purifiers

The air purifier uses either the corona discharge or UV light to break up the two oxygen atoms in dioxygen (the air we breathe) and allow them to combine again.  Most of the oxygen atoms reattach in pairs again.  Some may reattach in threes creating ozone which is believed to make the air cleaner and smell fresher.  Unfortunately, ozone is not a stable molecule.  It oxidizes metals and can attach to other atoms or molecules in the air to form more dangerous compounds.  Breathing in ozone can lead to health complications.

Government Oversight

Except for the HEPA standard, there is no government oversight on the other methods of air purification methods.

Other Ways to Clean the Air

An air purifier does not help if the source of air contamination is not removed.  Therefore, better solutions to cleaning the air indoors include removing the contaminants and opening windows to air out a place with fresh air.

Standardized Ratings

The Association of Home Appliance Manufacturers (AHAM) runs air purifiers through a standardized test and assigns ratings.  The rating is called the Clean Air Delivery Rate (CADR) and the higher the CADR the better.

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