Type Of Air Purifier - The Processes Used

I'm going to discuss the different types of air purifier technology and which types are best for removing particular air pollutants.
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. For these filters, the more surface area of carbon, which means the heavier they are, the more they can adsorb.

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.

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: 

• Ultra-violet germicidal irradiation
• Incineration
• 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:

• Pre-filter
• HEPA filter
• Electrostatic
• Ionization

Let's take a look at these in detail.

Pre-filter

Most air purifiers have a pre-filter which is usually 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.

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.

You should check that these devices don't produce more ozone than is healthy.

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 by-product. So, as with electrostatic devices, make sure the level of ozone is within limits.

Ozone Generators

I'm not recommending these for the average person because ozone is a toxic gas and shouldn't be used in any area which you are living in or using.

I hope this article gives you a good idea of the different types of air purifier processes. For reviews of actual air purifiers and more information articles, please visit Air Purifier Reviews.