The University of Texas at Austin
College of Engineering
IGERT - Indoor Environmental Quality
A Healthy Home is in Your Hands

air purifier

Portable Air Purifiers

What are portable air purifiers?

Portable air purifiers, also known as portable air cleaners, are devices that can be moved from room-to-room and set on a floor or table-top. They are meant to clean the air of pollutants in a particular room, rather than an entire home. Portable air cleaners are also commonly called air purifiers. These devices are generally not what people mean when they say "air filter", which usually refers to a filter for a heating, ventilation, and air-conditioning (HVAC) system. There are four main questions that customers may think of when they decide to buy a portable air cleaner:

What can a portable air cleaner remove from the air?

There are two main classes of pollutants that people use portable air cleaners to remove1,2,3,4 :

  1. Particulate matter (PM) - airborne particles are always present in our air, but in varying amounts. Increased exposure to outdoor particulate matter has been associated with increases in human mortality. Common types of particles indoors include dust, environmental tobacco smoke, pollen, and animal dander. Particles are also created from combustion appliances such as cooking stoves, and are associated with tiny organisms such as dust mites, mold, bacteria, and viruses.
  2. Gaseous compounds - these can originate from combustion processes, such as gas cooking stoves, vehicle exhaust, and environmental tobacco smoke. Many are also emitted indoors from building materials and furnishings, as well as the human use of products such as adhesives, paints, varnishes, cleaning products, and pesticides.


How to I choose a portable air cleaner?

You can compare different portable air cleaners by their effectiveness in reducing airborne pollutants. The current method to evaluate the effectiveness of a portable air cleaner is with the clean air delivery rate (CADR)2,3.5. The clean air delivery rate is the amount of completely contaminant-free air delivered by the device. CADR is typically expressed in cubic feet per minute, so if a portable air cleaner has a CADR of 250 for pollen, it will deliver 250 ft3/min of completely pollen-free air to the room.

A standard CADR test was developed by the Association of Home Appliance Manufacturers (AHAM)3. Manufacturers often have the CADR of their device determined by soliciting an independent lab to conduct the AHAM standard test. The results of this test are reported for dust, tobacco smoke, and pollen, and they are generally located on the back of the air cleaner box in the following format:

Clean Air Delivery Rate Label

If an air cleaner does not have the AHAM tested CADR on the back of the box, it will be difficult to compare the effectiveness of this air cleaner and should probably not be considered for purchase.


What are the common types of portable air cleaners?

There are a few main types of portable air cleaners on the market, and which type is best for you is determined by what you’re trying to remove in your air2,4,5.

  1. HEPA air cleaners - HEPA air cleaners are used to remove PM from the air. They use a fan to force air through filtration media. HEPA stands for High Efficiency Particle Arresting, and this classification refers to the filter media itself within the air cleaner. To be classified as HEPA quality, the filter media itself must be able remove 99.97% of any size particle passing through it.
  2. Ion generators and electrostatic precipitators - These devices are also used to remove PM from the air. They remove particles by using a corona to impart a negative charge on them so they can be removed to positively charged collector plates. The use of a corona generates ozone as a byproduct of its operation. Ozone is a respiratory irritant and a major driver of indoor chemistry. Ozone can react with common indoor compounds found in air fresheners, surface cleaners, and perfumes to actually produce liquid particles. Researchers have recently discovered that ozone generating air cleaners can actually produce more particles than remove in certain environments.
  3. UV air purifiers - These air cleaners use ultraviolet light (UV) to kill biological particles, including bacteria, mold, fungus, and viruses. These devices may be less effective than a filter at removing particles from the air.
  4. Hybrid purifiers - These devices contain two or more of the methods listed above.


Which air cleaner should I buy?

A HEPA filter with the best CADR for the money you want to spend is a good choice. Consumer Reports has published information on specific brands and types of air cleaners. We recommend you start there and don't just go out and buy blindly.


References:

  1. Offermann FJ, Sextro RG, Fisk WJ, Grimsrud DT, Nazaroff WW, Nero AV, Rezvan KL, Yater J. 1985. Control of respirable particles in indoor air with portable air cleaners. Atmospheric Environment 19(11): 1761-1771.
  2. Waring M., Seigel J., Corsi R. 2008 Ultrafine particle removal and generation by portable air cleaners. Atmospheric Environment, In press.
  3. ANSI/AHAM AC-1: Method for Measuring the Performance of Portable Household Electric Room Air Cleaners. http://www.aham.org/industry/ht/a/GetDocumentAction/i/12100, Accessed by April 21, 2008.
  4. Residential air cleaning devices: a summary of available information- EPA, http://www.epa.gov/iaq/pubs/residair.html, Accessed by April 21, 2008.
  5. Shaughnessy, RJ ; Sextro, RG, (2006) What is an effective portable air cleaning device? a Review. Journal of Occupational and Environmental Hygiene, 3(4), 169 - 181.