What Air Filters Do

• There are two types of pollutants that are commonly found in homes: gaseous pollutants and particulates. Particulates are small particles such as animal dander, dust, mold and pollen. Gaseous pollutants are things such as carbon monoxide, gases released by paint and varnish and pesticides. Residential air filters are good at removing particulate matter from the air, but not nearly as good at removing gaseous pollutants, which are made of much smaller particles. Residential air filters can be installed either as part of the central air system or placed in individual rooms as self-contained units.
  
  

Mechanical Air Filters

• Mechanical air filters are powered by a fan. Air is pulled through a paper or cloth filter such as a HEPA filter. The filter has tiny holes in it, big enough to let the air molecules through, but small enough to trap small particles. Many mechanical air filters also use an activated charcoal filter. Activated charcoal is an adsorbent material--something that is good at trapping particles on its surface. Activated charcoal filters can trap small particles and some gaseous pollutants as well.
  
  

Electrical Air Filters

• In an electrical filter, the air is also drawn through by a fan. It first goes between electrical plates which give it a negative charge. Then, the air flows past positively charged plates. The particles in the air already have a negative charge, so they stick to the positive plates. Some electrical filters called ion generators don't use the positive plates at all. Instead, they negatively charged the air which causes dust in it to clump together and stick to floors, tables and other surfaces where it can be vacuumed up later.