Air Purifier Glossary

Air Changes per Hour
Used to describe the amount of times every hour that an air purifier will re-circulate all of the air in a room through the filter. This is really important when choosing a HEPA type air purifier. Around five air changes per hour is recommended. Many off the shelf basic air
purifiers found on the High Street claim to be super effective, but only provide 1-2 air changes an hour in the room sizes they display on the box.  

Air Steriliser
A type of air purifier, such as AIRFREE, which cleans the air to the highest degree possible. This type of air purifier 'destroys' rather than captures airborne pollution. Biggest benefits are their ability to completely destroy all viruses, bacteria and microorganisms which usually pass
right through a standard HEPA filter type air purifier.     

A normal particle or substance which causes an acute defensive reaction in a person's immune system. Common allergens are pet dander, smoke, and pollen, although the list of possible allergens is long and varied. When a person has a reaction to an allergen that person is said to
be allergic to it. View our blog article 'What makes me allergy prone' for further information on this.

Animal Dander
Tiny scales of animal skin etc. The most acute allergen from a pet tends to be their saliva which when it dries, breaks into tiny weightless airborne particles. 

Air Quality Index (AQI)
The Air Quality Index is an index for reporting daily air quality. The index tells us how clean or polluted the air is currently, and what associated health effects might be a concern as a result. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.


Microscopic, single-celled organisms. There are many types of bacteria, and although many are harmful , there are some that actually help. We all carry good bacteria in our systems too!

Black Wall
An occurrence common with ionic air purifiers (Ionizers) that happens when the air around the air purifier becomes negatively charged. These negatively charged particles stick to the nearest surrounding surfaces and cause a build up of unsightly dirt and bacteria.

Corona Discharge
A type of air purifier that uses ozone to clean the air. The air inside a coronal discharge device is charged with between 5,000 and 10,000 volts of electricity. The shock causes unstable bonds to form between single atoms of oxygen (O) and Oxygen molecules (O2). Ozone
then attacks any airborne particles in the surrounding area (O3).

Clean Air Delivery Rate is a measure of the air purifier's ability to reduce smoke, dust, and pollen particles. CADR is defined as " The rate of contaminant reduction in the test chamber (1008 sq. ft) when the unit is turned on, minus the rate of natural decay when the unit is not running,
multiplied by the volume of the test chamber as measured in cubic feet. See here for a full definition

An airflow measurement of Cubic Feet Per Minute.

Electrostatic Precipitator
This type of air purifier operates by passing polluted air into a cell where it is then given a positive electrical charge. The air is then blown through steel plates which carry a negative charge and attract the dust and allergens from the charged air. This type of air purifier emits ozone as by
product which itself is a known allergy trigger. In our opinion this type of air purifier is probably best avoided.

Environmental Protection Agency, the agency responsible for the regulation of pesticides, toxic chemicals, hazardous wastes, and toxic pollutants in water and air.

Any porous device that allows the passage of air but traps airborne particles.

HEPA Filter
HEPA stands for High Efficiency Particulate Arrestor. HEPA filters are made from fibreglass triclosan paper. A filter is generally classed a 'true' Hepa filter if it filters out over 99.7% of particles above 0.3 microns in diameter. Some professional air purifiers actually filter out
particles as small as 0.1 micron, which means they are also dealing with many viruses too. Standard 0.3 Hepa filters cannot filter out many viruses at all as they are too small to be trapped in the filter matrix.

A substance your body injects into your bloodstream to help you stay alert. However, it is often triggered by allergens. It causes fluid to be released into the skin (which causes swelling and itching, and when released into the sinuses can cause an itchy, runny nose and watery eyes.

Indoor Air Pollution
The term used to describe the amount of contaminants in the air inside a building. Indoor air pollution can often be worse than outside air pollution due to poor ventilation. Unfortunately, it is often ignored. About 80 per cent of all indoor air pollution is human skin. The
remaining 20 percent is usually made up of dust mites, pet dander, smoke, pollen, sweat, and chemical compounds from various substances.

Indoor Air Quality (IAQ)
A term used to describe how polluted the air inside a confined space is. The IAQ of any building is measured according to guidelines set by the government and is used as a measuring stick for the efficiency of air purification and filtration systems.

Ionizers (Ionisers)
These use high voltage electricity to create negative electrons. These electrons run up the length of a pointed spike, or needle, where they stream into the air and attract oxygen molecules. At this point, they become negative ions and are attracted to airborne particles. These
molecules build up around the particles until they become too heavy to remain air borne and float to the ground. This process is known as agglomeration. Ionizers (Ionisers here in the UK!) are generally considered to be the lowest form of purification. A good hepa filter based air purifier is usually much more beneficial as it actually traps the particles inside and does not simply deposit them on the surfaces around the room.

One micron is 1/1000 mm (1/25,000 of an inch). Airborne particles are usually described in microns. Generally speaking, the human eye can see debris and dust that are approximately 25 microns in size.

Negative Ion
These are odorless, tasteless, and invisible molecules that we inhale in abundance whilst in certain environments such as around mountains, waterfalls, and beaches. Once they reach our bloodstream, negative ions are believed to produce biochemical reactions that increase our levels of
serotonin, thought to help alleviate stress and depression and to boost our energy. Many low brand air purifiers use the inclusion of negative Ions as a way of promoting the benefits of their product, when in essence the reality is that most air purifiers which rely on of this type of technology actually release ozone, itself a well known trigger for allergies. 

A special type of oxygen molecule caused by bonding a third oxygen atom to a pair of oxygen ones. This is usually accomplished using ultraviolet light. Ozone is highly unstable and reacts with air borne particles by launching the extra oxygen at anything nearby. The oxygen atom
reacts with the air borne particle, causing a tiny explosion and the destruction of the particle. Ozone purifiers can be highly effective against both dust and microscopic organisms, but can also be unhealthy if a person is exposed to large quantities.

The production of gases from the chemical deterioration of a substance over time. See VOC's Below.

A purifier is a device that cleans the air of airborne pollution such as dust, allergens viruses and microscopic organisms. Air purifiers can be especially useful for people who suffer from allergies or wish to remove odours from their environment such as odours from smoke, pets or cooking. 

UV Air Purifier
This type of air purifier uses ultraviolet light to purify the air. Ultraviolet radiation renders certain microorganisms sterile and harmless. Some basic air purifiers still use this technology. UV bulbs can be expensive to replace and other filtration methods such as air sterilisers or
medical grade Hepa air filters are much more effective.

Volatile Organic Compounds (VOCs)
Compounds that evaporate from household goods, cleaning products, and building products made with organic chemicals. Some people are highly allergic to these compounds and are often diagnosed as having MCS Multiple Chemical Sensitivity (MCS). In sufficient
quantities, VOCs can cause eye, nose, and throat irritations, headaches and dizziness.