Air Purifiers

As we spend over 90% of our time indoors, the quality of the air we breathe can have a phenomenal impact on our health and well-being. Sources of indoor pollution are varied and include the obvious such as tobacco smoke, indoor allergens, dust, pollen, mold spores and animal dander. Other often overlooked sources include the cleaning agents and air fresheners we use to improve the home. These agents can release volatile organic compounds (VOCs), as can certain paints, new pressed wood furniture and carpeting. These indoor pollutants have been linked to asthma, worsening of chronic medical conditions, and other serious health issues.

As our understanding of the adverse effects of indoor air pollution have grown, a new market has emerged in which a vast array of products and services related to indoor air quality have become available. When it comes to air purifiers it may seem as though there is a dizzying number of options from which to chose, with varying claims of health benefits. There are a few simple things you need to keep in mind when considering the appropriate air purifier for your needs.

There are 3 types of air purification processes: air filtration, air ionization, and ozonolysis. With air filtration, air is taken through a filter to remove particulates before being released into the room. Most ionic (air ionization) devices work by charging airborne particles and electrostatically precipitating them on metal blades which then need to cleaned. Ozonolysis air purifiers use a large amount of ozone with the intent of oxidizing volatile organic compounds. Unfortunately, this process can lead to the generation of even more hazardous materials than were in the environment to begin with. Both ozonolysis and some ionization purifiers generate ozone. Ozone in the home is a bad thing. Of the purification processes available, filtration of the air is by far the healthiest option.

Why do we care about the release of ozone? In 2005, the California Air Resources Board (CARB) issued an official statement expressing a serious concern about ozone-generating air purifiers and recommended that the public avoid these devices. In their report, CARB stated: “air cleaners that generate ozone intentionally should not be used indoors. Independent studies by the US EPA, the Consumers Union, and others have shown that these devices can emit very high amounts of ozone - several times the state ambient air quality standards. Additionally, ozone generators do not effectively destroy microbes, remove odor sources or reduce indoor pollutants enough to provide any health benefits (Indoor Air Pollution in California: Report to the California Legislature; California Air Resources Board: Sacramento, CA, 2005, ARB Warns, Danger from Popular “Air Purifying” Machines; ARB press Release 05-02, California Environmental Protection Agency: Sacramento, CA, 2005). Furthermore, the ozone generated by these devices can combine with air fresheners and cleaners to make toxic materials that are not easily cleared from the environment.

After eliminating devices that generate ozone from your search for the perfect air purifier, it is now time to examine the details of the remaining air cleaners which rely upon filters. HEPA (High Efficiency Particulate Air) filters remove 99.97% of all particles as small as 0.3 microns from the air that pass through them. Many advertisements give the misleading impression that any HEPA filter will clean the air in a room of more than 99% of its particles. The reality is that the amount of cleaning of the air in the room depends not just on the filter, but also on the amount of air moving through the filter. This is expressed as the “clean air delivery rate” or CADR. The EPA recognizes CADR as the appropriate test of air cleaner effectiveness.

The Clean Air Delivery Rate (CADR) is a measure of the amount of particle-free air being delivered into the room. The higher the clean air delivery rate, the larger the size room that can be effectively cleaned of airborne particles. The CADR allows for comparison among air cleaners. Typically a CADR greater than 350 is considered excellent. It needs to be noted that the advertised clean air delivery rate applies to the highest speed on the unit.

When choosing an air cleaner, it is also critical to choose one that can handle the size of the room you wish to clean. Air cleaners are typically advertised with the room size for which they are recommended. This recommendation is based on the unit’s ability to provide five or six air changes per hour in a room by 70%. A larger unit in the same size room can produce 8 or more air changes per hour, decreasing levels by 90% or more. This is the correct target in medical situations.

Ah, so what are our options?