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Introduction to Indoor Air Quality

Introduction to Indoor Air QualityIndoor air quality is a steadily increasing health concern. According to the EPA, pollutant levels are 2 to 5 times higher inside the home than out. These pollutants include airborne particles and particulate matter, which can be allergens or lung irritants, as well as gases, chemicals, and volatile organic compounds.

These sources of indoor pollution contaminate the air we breathe every day. Since people spend approximately 90% of their time indoors, it's obvious why indoor air quality is important to our health. We typically inhale what amounts to about two tablespoons a day of airborne particles. This causes stress to our bodies, leading to other health problems. The effect of poor indoor air quality on an individual can vary greatly based on their age and relative health. However, in general, poor IAQ causes allergy symptoms, respiratory problems, and a weakened immune system. If you are experiencing allergy symptoms or asthma attacks in your home, this may be a sign of poor IAQ. Other signs of an IAQ problem include a home with poor ventilation, lingering odors, or a change in environment such as recent construction, water damage, or a new pet.

What You Can Do

The EPA suggests three basic methods for improving indoor air quality: controlling the source, improving ventilation, and purchasing an air purifier.

The first step you take should always be an attempt to control the source. If the pollutant stems from something like mold, smoke, or chemical off-gassing, it may be possible to remove it from your home. This is the best and most permanent method for improving indoor air quality! However, some indoor air pollutants are too pervasive to be removed, such as dust or pollen.

Improving ventilation can help improve your indoor air quality if the offending pollutant is a chemical or gas. In this case, bringing fresh air into the home can be very helpful. However, some problems with indoor air pollution come from outside, so throwing open a window on a high pollen-count day or in a smoggy city may not be the best idea.

The third step suggested by the EPA is to purchase an air purifier. With so many types and brands of air purifiers on the market, it is pretty easy to find one that is well-suited to your home's particular situation. Quality air purifiers can work wonders on IAQ. However, some popular air cleaners on the market are not so good, and many air cleaners can cause some of the very problems they are meant to cure. See our list of the top five air purifiers for allergies.

Types of Indoor Pollutants

There are several main types of indoor pollutants. The most common complaints for allergy sufferers are common airborne particles pet allergens, pollens, dust, dust mite allergens, etc. These range in size from 0.3 to 100 microns, and are small enough to be inhaled, but too large to be easily exhaled. They are best removed using a HEPA filter.

Many other common indoor pollutants are simply household odors and gases. These pollutants include things like cooking smells, tobacco smoke, pet litter, and indoor pesticides. These can aggravate allergies and asthma.

Chemically reactive gases and volatile organic chemicals are another type of common indoor pollutant responsible for poor indoor air quality.  They are found in common household products like paints, cleaning supplies, disinfectants, and new carpets. They are especially harmful for chemical sensitivity sufferers, and they can be hazardous to your health if they are present in large enough quantities, or if your home is poorly ventilated. VOCs can cause symptoms like headaches, nausea, and throat irritation.

Types of Air Purifiers

HEPA Air Purifier
HEPA High Efficiency Particulate Air. A HEPA filter removes airborne particles like pet dander, mold spores, and dust, capturing 99.97% of all particles 0.3 microns and larger. This means that out of every 10,000 particles which pass through the HEPA filter, only 3 can escape, for it to be certified HEPA quality. The U.S. Department of Homeland Security recommends HEPA air purifiers, and it's the highest current standard in air filtration. In our opinion, a HEPA filter is a necessary requirement for an air purifier. When looking at a HEPA filter, consider aspects like the size and quality of the filter medium.

Activated Carbon Filter
Activated carbon removes gases, odors and toxins. Carbon is "activated" by treating it with oxygen, which opens up millions of tiny pores in it, creating a surprisingly large surface (one pound can have a surface area of 60 150 acres). Chemicals, gases, and odors stick to the carbon and are "adsorbed" onto its huge surface area, bonding to the surface through chemical attraction. The more carbon there is, the more gases and chemicals it can adsorb. Impregnated activated carbon has been treated with an additional chemical, typically potassium iodide or potassium permanganate. These chemicals are known as "chemisorbents" and they improve the carbon's ability to handle volatile organic chemicals and chemically reactive gases.

Electrostatic Filters
These types of filters use some kind of electrostatic charge to attract pollutants. Electrostatic precipitators are air cleaners which ionize particles as they are passed over an electronic cell, after which they are attracted and trapped by oppositely charged collector plates. The advantage of this is that there are no filters to replace; the disadvantage is that the effectiveness of the air cleaner decreases VERY rapidly as the collector plates fill up, and unless you are willing to wash them frequently, the air cleaner may become ineffective. Also, some of these types of machines may generate unsafe levels of ozone, which is a lung irritant.

Another type of filter which uses ionization is a charged-media filter. Charged-media filters charge particles, before collecting them in a traditional filter. They can trap very small particles, since they combine a filter and a charge. They can also run more quietly and economically, since the fan does not have to work as hard to draw the particles through the filter. However, like the example above, the charged-media filters lose their efficiency pretty rapidly, and can require frequent and expensive filter changes.

Ionization air cleaners and ozone generators
Ionization air purifiers operate by drawing in particles and ionizing them (giving them a negative charge). Then, the particles are released into the room, where they are attracted to positively charged surfaces like walls and furniture. This makes your house dirty, and the particles can be dislodged again by movements like walking or air circulation. Many ionization air cleaners generate ozone, which is a documented health hazard and lung irritant.
Another type of machine sold as an air cleaner is an ozone generator. Obviously, these types of machines are not recommended. The EPA has published documents discouraging the use of ozone generators as air cleaners.


Many homes have a variety of air contaminant sources to deal with, including both airborne particulates and allergens, and household chemicals and odors. We recommend an air purifier which combines a HEPA filter with some amount of carbon. This combination will remove the widest variety of indoor pollutants. For more information on air purifiers, visit our HEPA Air Purifier Buying Guide.