Types of Air Purifier And What Pollutants They Remove

I’m going to discuss the different types of air purifier technology and which types are best for removing particular air pollutants. If you react to a particular allergen, for example, you’ll want to know which type of air purifier removes it most efficiently. If your problems is formaldehyde, you’ll want to know the best way to remove it from your home. In these two cases the answer will be very different.

Be sure to check out my article on Indoor Pollution And Health Problems which has a lot of information about the types of air pollutants and what size the pollutants are.

There are three main categories of pollutants that you need to be concerned with:

1. Gaseous pollutants or volatile organic compounds (VOCs)
2. Bacteria and viruses. 
3. Particulate matter

These three need very different purification technologies. However, various technologies are often combined together in one air purifier model in order to increase its effectiveness in removing the full range of pollutants. Let’s look at each of these in turn.

Types Of Air Purifier For Gaseous Pollutants or Volatile Organic Compounds

Let’s take the gaseous pollutants or volatile organic compounds (VOCs) which are given off by various household furnishings and carpets and by various appliances and equipment. These can particularly affect people with asthma or multiple chemical sensitivities.  There are two effective types of air purifier to remove these from the air:

Activated Carbon Filters

The best way to get rid of these is by a process called adsorption which is done by activated carbon filters. Sometimes, potassium permanganate and/or zeolite is added to the carbon for a better effect.

The important factor with carbon filters is the weight of the carbon. The more activated carbon in the filter, the better and longer-lasting it will be for removing VOCs. For a good filter you are talking about 5 pounds of carbon and upwards. Usually you only get this kind of filter in the higher end air purifiers. The thin carbon pre-filters in cheaper models are no use except for removing larger particles and some odor.

Photocatalytic Oxidation (PCO)

A recent innovation to get rid of VOCs and also to kill bacteria and viruses is called photocatalytic oxidation. It uses ultra-violet light and a photocatalyst (usually titanium dioxide) to produce oxidants that destroy gaseous pollutants and oxidize bacteria and viruses. There are models which incorporate both carbon filters and VOCs and these models will clearly be very effective for VOCs and for bacteria and viruses.

Tobacco smoke has a gaseous component as well as particulate matter and if you want to get rid of the tobacco smell out of a room, an activated carbon filter or PCO air purifier will be most effective. In this case, you will also want a model with a HEPA or electrostatic filter to capture the particle elements of the smoke.

Types Of Air Purifier For Bacteria and Viruses

In the case of bacteria and viruses, you want to kill them rather than just collect them. There are three effective ways of destroying bacteria and viruses within an air purifier:

1. Ultra-violet germicidal irradiation
2. Incineration
3. Photocatalytic Oxidation

Let’s take a look at these one by one.

Ultra-Violet Germicidal Irradiation

This is basically a sterilization method using ultra-violet light. The UV light has to be at the right wavelength of which the most effective is 254 nanometers. At this wavelength the UV irradiation breaks the molecular bonds within DNA of microorganisms like viruses and bacteria. This destroys them or renders them harmless. It also destroys fungal spores and mold spores.

Incineration

The air is heated up to 400 degrees Fahrenheit or 250 degrees Centigrade within a sterilization chamber and the high temperature kills the microorganisms.

Photocatalytic Oxidation

As described above in the gaseous pollutants section, UV light shining on a titanium dioxide catalyst creates highly reactive oxidants which oxidise the microorganisms.

Types Of Air Purifier For Particulate Matter

For particulate matter like dust, dust mites, mold spores, pollen and pet dander, there are four main types of air purifier:

1. Pre-filter
2. HEPA filter
3. Electrostatic
4. Ionization

Let’s take a look at these in detail.

Pre-filter

Most air purifiers have a pre-filter which is a carbon filter designed to remove the coarser particles which would otherwise clog up the main filters or other processes within the purifier. It may remove some odor but shouldn’t be considered for serious odor removal.

HEPA filter

There are now replaceable true HEPA filters and permanent true HEPA filters which are designed to be cleanable but will eventually need replacing when efficiency starts to degrade. There are also HEPA-type filters which are cheaper but aren’t as efficient in removing the smaller particles. True HEPA filters capture at least 99.97% of all particles passing through the filter of 0.3 microns and less.

You should note that this is only particles passing through the filter. In some models where there is not a perfect seal between the filter and the unit, air can leak around the sides of the filter. So a good seal is another requirement for best performance.

Electrostatic

There are two types of electrostatic process but both work on similar principles. The airborne particles are  negatively charged within the unit and then collected either on a positively charged collection plate in the first method or in a positively charged filter in the second method. I think the first method is more common.

On point to be aware of is that these units can create ozone as a byproduct and you should check that it’s within required limits. You can Check the CADR website to see if they have certified it as within the ozone limits. CADR checks that the unit produces less than 50 parts per billion which is the level specified for medical products by the U.S. Food & Drug Administration.

However, even within limits, ozone is still a toxic gas and people vary in sensitivity to it, especially people with problems like asthma. Even in small amounts, in a closed room, it can gradually build up to unhealthy levels.

Ionization

Ionization  creates negative ions or in some cases negative and positive ions. The problem with this process is that it doesn’t actually remove pollutants from the room but causes them to stick to surfaces in the room  or to stick together and fall to the ground. This can lead to soiling of surfaces like curtains and carpets. It can also product ozone as a byproduct. So, as with electrostatic devices, make sure the level of ozone is within limits.

Ozone Generators – Not Recommended Under Any Circumstances

Ozone generators are special types of air purifier because they should not be used in a room you are actually using. For that reason, I can’t recommend them for an ongoing air purifier that you use day to day. There may be some case for using ozone generators in unoccupied spaces. They are effective for odors, tobacco smoke and mold.

Here is a quote from the Environmental Protection Agency website:

“However, little is known about the chemical by-products left behind by these processes (Dunston and Spivak, 1997). While high concentrations of ozone in air may sometimes be appropriate in these circumstances, conditions should be sufficiently controlled to insure that no person or pet becomes exposed. Ozone can adversely affect indoor plants, and damage materials such as rubber, electrical wire coatings, and fabrics and art work containing susceptible dyes and pigments (U.S. EPA, 1996a).”

Conclusion

I hope you’ve found the information of types of air purifier helpful.  You’ll find much more information on this website including individual air purifier reviews.

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