Passive Technology
The Air Filter

An air filter is what we would call a "Passive Technology" because the air must be drawn to and through the device, as opposed to "Active Technologies" which go out into the room and attack the pollution wherever it is found.

Depending on your choice of technology, both have their advantages and disadvantages. These will be discussed further as you read through the next few pages.

If you are already familiar with passive technologies and would like to see why active technologies can do a better job for you, go now to Active Technology, otherwise continue reading.

Aerosols
Aerosols is a term used to refer to airborne contaminants such as:

As you can see aerosols can have different chemical or biological characteristics but for the purposes of filtration we are only concerned with the physical size of the contaminant. Some particles such as dust can be visible but for the most part, these contaminants are microscopic. Particles vary in size from about 0.001 microns to about 100 microns. (an average hair is about 50 microns in diameter.

Click here to see a particle size comparison of some common components of indoor air pollution.

Is there a filter that will do what I need it to do?
If you give some thought to what you would like to accomplish, you should be able to pick a filter that can adequately clean the air in a single room. In fact, if size were everything, a few filters around the house would be all you need. Depending on the type of filters, you can even effectively remove or absorb some of the less obvious indoor air pollution such as gases and vapors from your indoor air.

Always keep in mind that filters will only address the issue of air-borne contaminants. I will expand on this point when we come to the pages dealing with air purifiers.

Again, depending on the problem, a filter may be just what you need. Be aware however, that sales literature can be misleading.

Let's examine some of the more popular types of filters available today:

Particle filter
The most common type of air filter in use today is the fibrous - particle filter.

Filter Devices
Depending on their usage, there are several types of filter devices.

HEPA Air Filters
The HEPA filter is very efficient at filtering air that passes through but has it's limitations.

Activated Charcoal
Many airborne contaminants are present in the form of gases and vapors which pass through most filters. The activated carbon filter uses absorption to capture these forms of pollution.