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If you've shopped for a household air cleaner or a filter for one lately, you've probably noticed the acronym HEPA. Pronounced like the first two syllables in hepatitis, it stands for high-efficiency particulate air. It describes the ability of the filter or air cleaner to capture particles. The acronym originated in World War II to describe filters used in gas masks, and a military specification was written to describe these filters. The specification requires that a HEPA filter remove at least 99.97% of the particles in the air down to three-tenths of a micron in size (a micron is one-millionth of a meter). Particles this small are troublesome. They are small enough to escape most types of filtration and are easily inhaled. It's no surprise, then, that particles that trigger asthma and allergies fall within this size range. If you buy an air filter, be sure it is a true HEPA - down to 0.3 micron or smaller sized particles and at least 99.97% efficiency.
Where can I find a good air purifier / HEPA filter?
See this page for much more detailed information about indoor air filtration.
Air Pollution Control
Air Pollution Monitoring
Air Pollution Legal Aspects
Why Be Concerned?
Effects of Air Pollution
What You Can Do!