Air filters are not able to completely eradicate the source of air pollutants in the home. For instance, some air filters can help reduce mold odors, but they won't solve the problem. To improve air quality, people must identify and eliminate the source of pollutants. Ionizing air purifiers can remove polluting particles from the air, but they have no effect on chemical exhaust fumes from cars.
Additionally, these types of air filters generate ozone as a side effect, which is a lung irritant. The Environmental Protection Agency (EPA) does not recommend using these types of air purifiers or any air purifiers that generate ozone. Air filters that meet certain standards can theoretically remove at least 99.97% of any particles in the air with a size of 0.3 microns (µm). This includes dust, pollen, mold and bacteria. However, other factors in the home can affect the effectiveness of an air filter, such as ventilation (windows open or closed) and new particles that constantly emerge.
The following publications provide information on portable air filters and heating and air conditioning filters that are commonly used in homes. To ensure that gases are also eliminated, it is important to make sure that any air purifier chosen has both a HEPA filter and an activated carbon filter. The longer technical guide focuses on air filters for residential use; it does not cover air filters used in large or commercial structures, such as office buildings, schools, large apartment buildings, or public buildings. This means that in addition to the purchase price of an air purifier, operating costs and filter replacement costs should also be taken into account. The higher the Clean Air Delivery Rate (CADR) number for each pollutant, the faster the unit filters the air for contaminants in a given size range.
In Utah winter, temperature reversals often trap cold, dirty air inside the Salt Lake Valley, giving Utah one of the worst air quality ratings in the country. To effectively remove pollutants from this type of environment, an activated carbon filter must be placed directly behind the HEPA filter. Many basic air purifiers that claim to have these filters inside only have an almost negligible amount of activated carbon inside and therefore only provide minimal protection. As air moves through the filter, contaminants and particles are captured and clean air is expelled into the living space. Some air purifiers use ionizers to help attract particles such as static negative ions that bind to dust and allergens and cause them to be deposited out of the air.
The Appliance Manufacturers Association (AHAM) recommends that the CADR of your air purifier be equal to at least two-thirds of the area of the room. There is some debate surrounding how effective air purifiers are at reducing larger particles (such as pollen, house dust allergens, mold spores, and animal dander), but most of these large particles are deposited on home or office surfaces and cannot be removed with an air cleaner unless altered and resuspended in the air.