There are three forms of junk in the air. First are particles like mold, dust, dust mites, pet residues like cat dander, and pollen, followed by bacteria and viruses that are particularly useful for people with weak immune systems, young infants, the elderly, and anyone with bronchitis or asthma. The third form of impurities in the air is gas given off by your television, new carpet or paint, and cleaning products that are toxic to humans and can cause cancer.

The kind of air purifier you purchase must match your environment. That means the air purifier system must physically remove vapors and particles. If the unit doesn't trap molecules, they are still in your environment. Models that generate ozone have been known to change lung tissue and trigger asthma attacks; ionizers are one type of air purifier that uses ozone.

Next, decide where you want to put the air purifier. Different models of air purifiers cover different areas of square feet. This means deciding on the size of room you would like to cool, or the size of the air purifier system you would like to purchase.

The last details you need to choose an air purifier are the features, from how many speeds to filter or filterless units. Air purifiers with HEPA filters will remove at least 99.97% of particles that are greater than 0.3 microns. Carbon filters – with as many pounds as possible - will remove chemicals and odors. In addition, if you are trying to alleviate tobacco smoke, make sure to purchase a unit specially designed for it, as the tars in the smoke can coat the carbon filter and render it inaccessible.

Finally, never buy an air purifier that is too small for the space where you want to purify the air. Make sure the purpose matches the power.