Air Purifiers

Air Purifier Technologies

Air purifiers can generally be divided into two types: mechanical and electronic. In this section we have further divided the types to give you an overview of six different technologies for home air purification systems in the market today, including a discussion of the safety and effectiveness of each.

Activated Carbon

Activated granular carbon is among the most effective materials known today for treating airborne chemicals, gases and odors. It is used widely by the military, hospitals, scientific and industrial facilities, and disaster response units for its safe and powerful adsorbing properties.

Carbon is safe because it is inert. It is so effective because it is an extremely porous substance; the surface area of one gram of activated granular carbon can be thousands of square meters.

This type of carbon is preferred for all 'adsorption' of gases and vapours as their rate of diffusion are faster. Granular carbon is processed so that it becomes more porous or 'activated' in order to trap more chemical pollutants.

As chemicals pass over the activated carbon, they are 'adsorbed', a process in which chemicals bond to the surface of the carbon; that is, they are 'trapped'. Once the chemicals are bonded to the carbon, they have been filtered and removed from the air.

Carbon is part of every living organism on earth, and the carbon used in air purifiers can be derived from many different sources such as peat moss, anthracite coal or coconut shells. Different carbon sources have slightly different chemical properties, making specific blends of carbon more effective for individual chemicals.

Coconut carbon is an example of an effective adsorbent of odors, gases and chemicals, especially in combination with zeolite. The zeolite draws moisture away from the coconut and also adds adsorption capacity for specific chemicals such as ammonia.

Carbon does not filter out every gas in the air (for example it leaves in the oxygen) but it is the most tried-and-true chemical filtration technology. Respirators (gas masks) used by the military use activated carbon.

The effectiveness of activated carbon filters are based on two main factors. First, the amount of carbon used is important. Many purifiers truthfully claim to use activated carbon, but they only use it in a very small amount which will quickly lose its effectiveness. Also, dwell time (the time that the air spends passing through the carbon) influences the effectiveness of the filtration process. The depth of the carbon filter (deeper filters add dwell time) and the speed of the motor (slower speeds add dwell time) are the main factors that affect the dwell time.

Even heavy duty activated carbon filters must be replaced occasionally; for the average home it is about once every 2 to 5 years, though in highly chemical environments it may be more frequently. A carbon filter does not remove particles, though it is generally coupled with a HEPA or other particle filter in most air purifiers.

Activated carbon is the substance that keeps military personnel safe from poisonous gases. It can adsorb up to 60% of its weight and can be effective for up to 2 years. Our air purifiers are known for having the most carbon in the industry. Together the true HEPA and activated, granular carbon provide the safest, most complete, and versatile air cleaning system available.

Overall, carbon filtration is the only mainstream and safe method for gas removal, and it is highly effective.

HEPA Filter

Short for 'high efficiency particle arrestor', HEPA is the most common particle filtration technology used in the air purification industry. Developed by the US Department of Energy to trap radioactive particles, today it is the standard filter used in medically clean rooms such as surgical theatres and laboratories.

There are imitation versions of HEPA which are not as effective in particle filtration. True medical-grade HEPA is made of densely compact, randomly arranged fiberglass fibres, a true medical-grade HEPA filter, by definition, is 99.97% effective at removing airborne particles 0.3 microns in diameter. Particles of this size are the most difficult to filter and are thus considered the most penetrating particle size (MPPS).

Particles that are larger or smaller are filtered with even higher efficiency than 99.97% by a true HEPA filter. HEPA filters efficiently trap a broad range of airborne pollutants including dust, pollen, pet dander, mold, bacteria and viruses. Usually in a high efficiency air purifier, pre-filters are used to extend the life of the HEPA filter by first trapping the larger particles such as dust, hair and pollen.

A micron, or micrometer, is 1/1000 of a millimetre or one millionth of a metre.

Examples of approximate ranges of particle diameters:

• • typical house dust mites, 10 to 300 microns
• • human hair, 60 to 300 microns
• • pollen and plant spores, 10 to 100 microns
• • bacteria, 0.3 to 10 microns
• • dust irritating to our breathing passages, less than 10 microns
• • virus, usually less than .3 microns

The key measurements affecting the function of the HEPA filter are its fibre density and diameter, and the filter thickness. Particles are mainly trapped by one of three mechanisms: interception, impaction and diffusion. These processes are related to the HEPA fibre, lines of airflow and velocity of airflow and are more complicated than a simple sieve action.

The effectiveness of HEPA filters is also dependent on how they are installed. This is one of the reasons that some air purifiers claim different effectiveness ratings despite the fact that they are using the exact same filtration material. The biggest factor influencing the effectiveness of HEPA filters is the seal around them. If air can bypass the HEPA filters by seeping around them, it is not going to get filtered properly and the "99.97% effective" rating can decrease considerably.

Also, the way HEPA filters are rolled and pleated influence their efficiency. HEPA filters should be rolled when they are warm to eliminate cracks, and they should be evenly pleated to make sure that the air does not go through a single part of the filters more than any others.

There is a cost in maintaining a HEPA air purifier, since filters need to be replaced. However, in an average home environment, HEPA filters can be effective for up to 5 years when pre-filters are changed regularly.

Overall, HEPA filters are extremely effective at removing airborne particles including dust, pollen, mold, bacteria and viruses. Because respirable particulate including bacteria and other minute airborne contaminants are trapped in the HEPA filter, the use of HEPA filtration, when properly applied, will significantly eliminate or reduce the deleterious health effects of airborne contaminants on the respiratory system.

HEPA filtration is the safest, most efficient and effective method to treat airborne particles.

Air purifiers which combine both HEPA filters and activated carbon filters are excellent for filtering both gases and particles. These air purifiers are especially useful for sensitive individuals.

UV Light

Ultraviolet (UV) light can be used to destroy biological contaminants such as bacteria, viruses, molds. However it is generally not effective for reducing airborne chemicals, gases and odors.

UV light breaks down the DNA of microbes so they cannot replicate. This neutralizes them, rendering them harmless.

If it is properly housed inside the purifier, germicidal, non-ozone producing UV technology is safe. In order to be effective, the pollutants need to be trapped near the UV light to give enough time for the DNA to be broken down. For example, if the UV lamp is installed facing a HEPA filter, the particles are well exposed to the destructive ultraviolet light.

For eye safety, it is wise not to look at a connected UV lamp for any length of time.

Electrostatic Precipitators

Electrostatic air purifiers are electronic air cleaners which use charged plates to attract and trap particles that pass by them. Generally, a fan pulls the air into the purifier. When the airborne particles receive a static charge, the charged particles will stick to the plates.

Electrostatic air purifiers are safer than ionizers and ozonators. However, there are two major downsides of electrostatic air purifiers. First, electrostatic technology by itself is not designed to eliminate airborne chemicals, odors or gases; the only chemicals and gases these air purifirs remove are those which are carried by the particulate they capture. Secondly, charged plates must be cleaned or replaced frequently, otherwise their efficiency is drastically reduced very quickly.

Another caution is that electrostatic air cleaners with electrically charged plates produce some level of ozone; ozone is a lung irritant. And if any charged particles escape from an electrostatic air purifier and then are inhaled, this also could irritate sensitive lungs.

Static electricity created by air flow through a medium such as an electrostatic furnace filter is not induced with electrically charged plates and is not as likely to produce ozone. However, because of their limited ability to collect airborne chemicals, odors and gases, these filters may be most helpful when used in conjunction with deep-bed carbon air purifiers.

Ion Generators

Ionic air purifiers, also known as ionizers, are electronic air cleaners that release positive or negative ions into the air to charge airborne particles and make them cling to nearby surfaces like walls and chairs, thus removing them from the air. However, the surfaces to which the particles stick can become quite dirty and need to be cleaned frequently.

Abrasion or a breeze can stir up the particles so that they are circulated back into the air again if they are not collected on a filter. These charged particles, if inhaled, can cause damage to the lungs.

Many ionic air purifiers release a small amount of ozone which can be toxic, especially for sensitive lungs. Ionic air purifiers do not remove gases or odors at all. To address this issue, some ionic air purifiers are coupled with ozone-emitters which are dangerous.

Ozone Generators

Lung associations, government organizations, scientists and medical professionals warn us about the hazards of ozone generators.

Ozone air purifiers are electronic air cleaners that generate ozone.

What is Ozone?

However, according to the EPA, "Available scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor air contaminants."

This means that to be effective at removing chemicals, viruses, bacteria, mold or other biological pollutants, the amount of ozone needed is dangerous to humans.

For restoration and industrial purposes, ozone should be used in UNOCCUPIED areas only.

An ozone air purifier does not remove airborne particles such as dust or pollen.

How is Ozone Harmful?

When inhaled, ozone can irritate the bronchi and damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation.

An ozone air purifier may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections. People vary widely in their susceptibility to ozone.

Healthy people, as well as those with respiratory difficulty, can experience breathing problems when exposed to ozone.

Exercise during exposure to ozone causes a greater amount of ozone to be inhaled, and increases the risk of harmful respiratory effects.

Recovery from the harmful effects can occur following short-term exposure to low levels of ozone, but health effects may become more damaging and recovery less certain at higher levels or from longer exposures.

The phrase "good up high—bad nearby" has been used by the U.S. Environmental Protection Agency (EPA) to make the distinction between ozone in the upper and lower atmosphere. Ozone in the upper atmosphere—referred to as 'stratospheric ozone'—helps filter out damaging ultraviolet radiation from the sun. Though ozone in the stratosphere is protective, ozone in the atmosphere—which is the air we breathe—can be harmful to the respiratory system.

Summary

Electrostatic air purifiers, ionic air purifiers and ozone producers are all electronic air cleaners. They all can produce ozone in varying amounts. Since ozone is a respiratory irritant, we do not recommend any of these three types of air cleaners.

Electrostatic and ionic air purifiers do not remove airborne chemicals, gases and odors (other than removing particles which may be carrying these extra pollutants).

Ozone air purifiers do not remove particles, and the safety level of ozone at which they remove chemicals, gases and odors is questionable at best.

Most air cleaners on the market today are not effective at removing odors, gases and chemicals, since they do not have deep bed activated granular carbon filters.

True medical grade HEPA filters are the best for removing fine particulate matter such as mold spores, dust mites, and bacteria.

Ultraviolet lamps which are germicidal (no production of ozone) are suitable in some situations that call for destroying biological pollutants such as mold, bacteria and viruses.