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Air purifier terms - a glossary
HEPA filter / "true HEPA" filter HEPA filter / "true HEPA" filter HEPA stands for High Efficiency Particulate Air or High Efficiency Particulate Arrestance. A HEPA filter is a highly efficient form of air filter which is designed to remove very small particles from the air. HEPA filters are often used in commercial and residential air purifiers, and in vacuum cleaners - as they excel at removing particles such as pollen, mold and dust from the air. HEPA filters are also often found in medical applications - a good indicator of their quality. Please see our full article on HEPA filters for more info. ULPA filter ULPA stands for Ultra Low Penetration Air. An ULPA filter by definition removes 99.999% of particles .00012 of a millimeter in size. Serious stuff! ULPA filters have an even higher rating and filtration effect than HEPA filters and are some of the highest grade filters around for removal of particulate matter from the air. However, because the ULPA material is more dense than that of a HEPA filter, airflow is more restricted - meaning less air circulation. ULPA units do not necessarily perform as well as HEPA units in providing particle-free air as they may not "change the air" in a room as frequently as a HEPA unit - due to restricted airflow. HVAC HVAC stands for Heating, Ventilation and Air Conditioning. Ionizer / Ionic Air Purifier An Ionizer / Ionic Air Purifier produces negatively charged "ions" - electronically charged air molecules which attract dust and other particles. This has a cleaning effect on the air as the particles which have clumped together fall from the air. The fact that this works can be demonstrated - as dust can be seen to collect near an air ionizer after it has been switched on for a while. Ionizers are quiet in operation but recent research and consumer reports have claimed that ionizers do not perform anything like as well as HEPA filters in cleaning the air. Also, they are believed to produce small amounts of ozone, a lung irritant. However, some believe that negative ions themselves have health benefits and may counteract the positive ionization of the air caused by other electronic devices. Here at air-purifiers-online though, we have to say that we are "bigger fans" of HEPA filtration.... :) Electrostatic / electronic air cleaners These use electricity to charge particles in a similar manner to an ionizer. These particles then collect on plates charged with the opposite charge. Gas Phase Air Filter / Activated Carbon Filter Also known as air scrubbers, these are used to remove Volatile organic compounds (VOCs), solvents, tobacco smoke, gases and odors from air.
The most common Gas Phase Air Filter is the Activated Carbon Filter. Activated carbon is a type of carbon that has been specially treated with Oxygen in order to open up pores between the carbon atoms and create a form of carbon with an enormous surface area - hundreds of square metres of "bonding sites" per gram! This means that chemicals which are "attracted" to carbon (such as chlorine and many VOCs) will have a great opportunity to be "adsorbed" by it. However, not all chemicals react with activated carbon and some will pass right through. It stands to reason that the most effective activated carbon filters will be ones which contain the most activated carbon! These however are thicker and are therefore more resistive to airflow. Some ACFs currently on the market contain many pounds of activated carbon. Activated carbon is also not suitable for removing dust from the air and so is often used together with HEPA filtration for an overall combined air filtering effect. Also, as already noted, activated carbon filters will not remove every type of gaseous pollutant from the air. In particular, carbon monoxide may be left behind. Thus activated carbon is often mixed with other substances which remove other types of gaseous contaminants from the air - such as Potassium Permanganate (which is intended to remove formaldehyde, hydrogen sulfide, and sulfur dioxide). Such products would appear to be able to address a wider range of gaseous pollutants. However, some say that Potassium Permanganate filters can possibly release Manganese into the air. (source: http://www.allerair.net/buyers_beware.html ) Zeolite (intended to remove ammonia) is also sometimes included in activated carbon filters but its effectiveness has been strongly challenged. Ultraviolet Germicidal Irradiation air cleaners These use UV light to kill viruses, bacteria and molds and are commonly used in HVAC systems in conjunction with particle filters such as HEPA. Ultraviolet light is a well known method of sterilization and has been used for this purpose since the 1930's. Photocatalytic Oxidation cleaners These use UV light in conjunction with a catalyst to convert harmful gases into harmless substances, but the United States Environmental Protection Agency states that their effectiveness is not currently sufficient for home air purification uses. Ozone generators These create ozone but are highly controversial, since ozone is toxic and a lung irritant. Ozone generators are often used in cleanup processes after fires or crime scenes, but the United States Environmental Protection Agency has deemed ozone generators unsafe and ineffective for general use as air purifiers and strongly recommends that they are not used for general air purification purposes. MERV rating
This stands for Minimum Efficiency Reporting Value - and is a scale measuring the effectiveness of air fliters. The MERV rating scores filters in HVAC (heating, ventilating and air conditioning) systems from 1 to 16 - the higher the number, the more efficient the filter. Because the material used to make a true HEPA filter needs to be more dense than that of a less efficient filter, true HEPA filters are not normally installed in HVAC systems. A true HEPA filter in such a system would cause too great a resistance to airflow - but according to the EPA, filters with a MERV rating of 7 to 13 are almost as efficient at removing small particles from the air.
Standalone HEPA filter units are often less expensive to run continuously than an HVAC system.
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