Technology

Ozone-emitting purifiers are dangerous.

There are several different air purification technologies available on the market today. One of these, purification with ozone, is actually dangerous to human health but many regulatory agencies are incapable of doing anything about it even though they know of the dangers.

Here is a brief description of the most widely used technologies in air purification today. Included is a discussion of their safety and their effectiveness.

Activated Carbon HEPA Filter Ion Generators Electrostatic UV Light Ozone-emitting technology

Activated Carbon

Activated carbon is the most effective chemical filtration technology. It is an extremely porous substance; the surface area of one gram of activated carbon can be thousands of square meters. As chemicals pass over the activated carbon, they are “adsorbed”, a process in which chemicals bond to the surface of the carbon. 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. Carbon doesn’t filter out every gas in the air (for example it leaves it 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 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, influence 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.

Carbon filters must be replaced occasionally; for the average home it is about once every two years, though in highly chemical industrial environments it may be more frequently. Overall, carbon filtration is the only mainstream and safe method for gas removal, and it is highly effective. It is an inert substance and is safe. A carbon filter does not remove particles, though it is generally coupled with a HEPA or other particle filter in most air purifiers.


HEPA Filter

Short for high efficiency particle arresting filter, HEPA is the most common particle filtration technology used in the air purification industry. Developed in the 1970s by the US Department of Energy, today it is the standard filter used in clean rooms, hospitals and laboratories. A HEPA filter, by definition, is 99.97% effective at removing particles of 0.3 microns in size. However, the true effectiveness of the HEPA filter is dependent on how it is installed.

This is the reason 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 a HEPA filter is the seal around it. If air can bypass the filter by seeping around it, it is not going to get filtered properly and the "99.97% effective" rating can decrease considerably. Also, the way the HEPA is rolled and pleated influences its effectiveness. HEPA should be rolled when it is warm to eliminate cracks (it is a glass-based material) and should be evenly pleated to make sure that the air does not go through a single part of the filter more than any others.

In an average home environment, a HEPA filter must be replaced approximately every 5 years. Overall, a HEPA filter is extremely effective at removing all airborne particles including mold, dust, pollen, bacteria and viruses (a properly installed HEPA filter is still extremely effective at filtering particles smaller than 0.3 microns, which most viruses are). A HEPA filter is not designed for filtering gases. In some air purifiers it is used along with a carbon filter so that the total air purifier filters gases and particles. It is a safe technology.


Ion Generators

Ion generation technology releases positive or negative ions into the air that charge airborne particles and make them cling to nearby surfaces like walls and chairs which removes them from the air. This is a viable method for particle removal, though the process is not standardized. This makes it very difficult to judge the true effectiveness of the many products that are on the market. Also, many ion generators release a small amount of ozone which is toxic. Ion generators do not remove gases (or odors) at all. Because of this, some ion generators are coupled with ozone-emitters and these are dangerous. Overall, ion generators do have some effectiveness for airborne particle removal, but their effectiveness varies and they don't remove chemicals/gases.


Electrostatic

These air purifiers use charged plates to attract and trap particles that pass by them. Generally, a fan pulls the air into the purifier. By giving the particles a static charge, the charged particles will stick to the plates in the electrostatic purifier. For particle removal, an electrostatic purifier is quite effective. The two major downsides of this type of purifier are the lack of chemical filtration and the regular maintenance; an electrostatic filter does nothing to eliminate gases or odors, and the charged plates must be cleaned frequently. Overall, an electrostatic purifier is effective for particle removal and ineffective for gas removal. It is a safe technology.


UV Light

Short for ultraviolet light, UV can be used as an anti-microbial filtration technique. UV light breaks down the DNA of microbes (such as bacteria, viruses and mold) and makes it so they cannot replicate. This neutralizes them, rendering them harmless. In most air purifiers that are equipped with this technology, the UV bulb is inside of the housing. If it is properly housed inside the purifier, UV technology is safe. People should not stare at a UV bulb for an extended period of time.



Ozone-emitting technology

Ozone (O3) is a chemical made of three oxygen atoms. It is an unstable molecule and it is due to this property that it is used in air purification. The ozone will react with other chemicals, changing their molecular structure.

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 or preventing bacterial or mold growth (two uses of ozone) the amount of ozone that would need to be used would be dangerous to humans. Thus, ozone purification is either dangerous or ineffective. Also, ozone does not remove airborne particles such as dust or pollen. To read more on what the EPA has to say about Ozone-emitting air purifiers, click here.