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Indoor Air Quality


Glossary over Indoor Air Quality


An aerosol is a collection of microscopic particles, solid or liquid, suspended in a gas.

In the context of air pollution, an aerosol refers to fine particulate matter, that is larger than a molecule, but small enough to remain suspended in the atmosphere for at least several hours.

The term aerosol is also commonly used for a pressurized container (aerosol can) which is designed to release a fine spray of a material such as paint. It has also come to be associated, erroneously, with the gas (propellant) used to expel materials from an aerosol can. (Source: GreenFacts )



Allergies are inappropriate or exaggerated reactions of the immune system to substances that, in the majority of people, cause no symptoms.

Symptoms of the allergic diseases may be caused by exposure of the skin to a chemical, of the respiratory system to particles of dust or pollen (or other substances), or of the stomach and intestines to a particular food. (Source: ACAAI Allergy-Immunology Glossary  )



Thin-walled, tiny air sacs located at the ends of the smallest airways in the lungs (the bronchioles) where the exchange of oxygen and carbon dioxide takes place. (Source: GreenFacts, based on WebMD Asthma Glossary of Terms  )



A usually chronic inflammatory disorder of the airways characterized by intermittent episodes of wheezing, coughing, and difficulty in breathing, sometimes caused by an allergy to inhaled substances. (Source: American Lung Association Appendix 4: Glossary  )


Bacteria are a major group of micro-organisms that live in soil, water, plants, organic matter, or the bodies of animals or people. They are microscopic and mostly unicellular, with a relatively simple cell structure.

Some bacteria cause diseases such as tetanus, typhoid fever, pneumonia, syphilis, cholera, and tuberculosis.

Bacteria play a role in the decomposition of organic matter and other chemical processes. (Source: GreenFacts)



A volatile liquid solvent found in gasoline, with formula C6H6, that is used widely by the chemical industry. It is found in tobacco smoke, vehicle emissions and gasoline fumes.

Benzene exposure can cause cancer and other health complications. (Source: GreenFacts)


Inflammation of the bronchi, the main air passages that lead to the lungs.

Bronchitis causes a persistent cough and phlegm production. It is especially common in smokers and in areas with atmospheric pollution. (Source: GreenFacts based on Urologychannel HC Glossary )



Any one of a group of diseases that occur when cells in the body become abnormal and have the potential to spread and establish growth in nearby tissues and other parts of the body (malignancy). (Source: GreenFacts )


Carbon dioxide (CO2)

A colorless, odorless, non-combustible gas, present in low concentrations in the air we breathe (about three hundredths of one percent by volume).

Carbon dioxide is produced when any substance containing carbon is burned. It is also a product of breathing and fermentation. Plants absorb carbon dioxide through photosynthesis. (Source: The Pacific Forest Trust Glossary )


Carbon monoxide (CO)

An odorless, colorless, and highly poisonous gas.



The basic subunit of any living organism; the simplest unit that can exist as an independent living system. There are many different types of cells in complex organisms such as humans, each with specific characteristics. (Source: GreenFacts)



Occurring over a long period of time, either continuously or intermittently; used to describe ongoing exposures and effects that develop only after a long exposure. (Source: US EPA Thesaurus  )

Circulatory system

The system that contains the heart and the blood vessels and moves blood throughout the body. This system helps tissues get enough oxygen and nutrients, and it helps them get rid of waste products. The lymph system, which connects with the blood system, is often considered part of the circulatory system. (Source: NCI Dictionary of cancer terms  )


Climate change

The long-term fluctuations in temperature, precipitation, wind, and all other aspects of the Earth's climate.

It is also defined by the United Nations Convention on Climate Change as “change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods” (Source: CoRIS glossary  )

Coarse particles

Particulate matter present in air is divided into different categories depending on the size of the particles (aerodynamic diameter).

Coarse particles are the relatively large airborne particles mainly produced by the mechanical break-up of even larger solid particles.

Examples of coarse particles include dust, pollen, spores, fly ash, and plant and insect parts.

Coarse particles have an aerodynamic diameter ranging from 2.5 to 10µm (PM10-2.5), which distinguishes them from the smaller airborne particulate matter referred to as fine (PM2.5) and ultrafine particles (PM0.1).


A material made up of two or more elements combined in a fixed ratio. (Source: CoRIS glossary  )


Confounding factor

A confounding factor in a study is a variable which is related to one or more of the variables defined in a study. A confounding factor may mask an actual association or falsely demonstrate an apparent association between the study variables where no real association between them exists. If confounding factors are not measured and considered, bias may result in the conclusion of the study. (Source: GreenFacts)


A substance that is either present in an environment where it does not belong or is present at levels that might cause harmful effects to humans or the environment. (Source: GreenFacts)

Coronary heart disease

Coronary heart disease is atherosclerosis of the coronary arteries, i.e. a "hardening" of the walls of the small blood vessels that supply blood and oxygen to the heart (coronary arteries).

This hardening is due to fatty deposits called plaques that build on the inner walls of these arteries.

The resulting narrowed passageway decreases or stops the flow of oxygen-rich blood to the heart, which damages the heart muscles and leads to chest pain, shortness of breath, heart attack, and possibly to death. (Source: GreenFacts)


Dose-response relationship

The relationship between the amount of exposure [dose] to a substance and the resulting changes in body function or health (response). (Source: ATSDR Glossary of Terms  )


Epidemiological studies

Studies on human populations, which attempt to link human health effects (e.g. cancer) to a cause (e.g. exposure to a specific chemical). (Source: GreenFacts)


Fine particles

Particulate matter present in air is divided into different categories depending on the size of the particles (aerodynamic diameter).

Fine particles are airborne particles which are smaller than coarse particles. They have an aerodynamic diameter of 2.5 µm or less (PM2.5). The fine particles which are smaller than 0.1 µm are referred to as ultrafine particles (PM0.1).

  • Fine particles are largely formed from gases.
  • Ultrafine particles are formed by nucleation, which is the initial stage in which gas becomes a particle. These particles can grow up to a size of 1µm either through condensation, when additional gas condensates on the particles, or through coagulation, when two or more particles combine to form a larger particle.

Please note that ultrafine particles (PM0.1) are part of the fine fraction (PM2.5). (Source: GreenFacts)


The embryo is referred to as a foetus after it has reached a certain stage of organ development (in humans this is eight weeks after conception). (Source: CSIRO Glossary of terms  )


A colorless, pungent, and irritating volatile organic compound (VOC), with formula H2CO, used in manufacturing and chemical industries, and as a preservative by anatomists, embalmers, and pathologists. Potential sources in the home include pressed wood products such as particleboard or fiberboard, smoking, glues and adhesives, etc.

Formaldehyde is a known human carcinogen. (Source: GreenFacts)


Any of a group of plant-like microorganisms that include molds, mildews, mushrooms and yeast.

Fungi lack chlorophyll and use living or dead organisms as food by breaking them down and then absorbing the substances into their cells. Many fungi reproduce by disseminating spores which are transported by air and await proper conditions of moisture and temperature to germinate, grow and reproduce. (Source: GreenFacts )


The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein. (Source: NHGRI Talking Glossary of Genetic Terms  )

Immune system

The immune system is a network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders. (Source: NIAID Immune System   )



Inflammation is the reaction of living tissues to infection, irritation or other injury. (Source: GreenFacts)



The act of swallowing something through eating, drinking, or mouthing objects. A hazardous substance can enter the body this way. (Source: ATSDR Glossary of Terms  )


The act of breathing.

A hazardous substance can enter the body by inhaling an airborne substance or contaminant in the form of gas, fumes mists, vapors, dusts, or aerosols. Once inhaled, contaminants can be deposited in the lungs and/or transported into the blood. (Source: GreenFacts)


A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by […] laws and regulations. (Source: US EPA  Glossary )

Mean / Median

In statistics, mean and median both provide an idea of where the “middle” of a sample is.

The mean (or average) is the sum of all scores divided by the number of scores. For instance the sum of individual ages of persons in a group divided by the number of persons in the group, gives the average age.

The median is the number in a range of scores that falls exactly in the middle so that 50% of the cases are above or below. (Source: GreenFacts)



Any living organism that is too small to be seen by the naked eye such as bacteria, viruses, protozoa, single-celled algae, and many types of fungi. (Source: GreenFacts)


Parasitic, microscopic fungi (like Penicillin) with spores that float in the air like pollen. Mold is a common trigger for allergies and can be found in damp areas, such as the basement or bathroom, as well as in the outdoor environment in grass, leaf piles, hay, mulch or under mushrooms. (Source: WebMD Asthma Glossary of Terms  )

Mucous membrane

The moist layer of tissue lining the digestive, respiratory, urinary and reproductive tracts - all the body cavities with openings to the outside world except the ears. (Source: Medical dictionary   )


Particle with one or more dimensions of the order of about 100 millionth of a millimetre (100 nm) or less.

(Note: In the SCENIHR  opinion on the appropriateness of existing methodologies to assess the potential risks associated with engineered and adventitious products of nanotechnologies, nanoparticles are considered to have two or more dimensions at the nanoscale) (Source: GreenFacts )


A volatile organic compound (VOC) [with formula C10H8] that is naturally present in fossil fuels such as petroleum and coal, and is produced when wood or tobaccoare burned. Naphthalene is used in the production of many products, including dyes, pharmaceuticals, and insect repellents, such as moth balls. Releases of naphthalene to the environment are widespread.

In humans, exposure to large amounts of naphthalene may damage or destroy red blood cells, causing hemolytic anemia [a condition where the red blood cells break up, resulting in fewer red blood cells]. (Source: San Diego Bay Watersheds Glossary  )

Nervous system

The nervous system is a complex, sophisticated system that regulates and coordinates body activities.

It is made up of:

  • the central nervous system, consisting of the brain and spinal cord, and
  • the peripheral nervous system which includes, the eyes, the ears, the sensory organs of taste and smell, as well as the sensory receptors located in the skin, joints, muscles, and other parts of the body.
Nitrogen oxides (NOx)

NOx is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts [such as nitric oxide (NO) and nitrogen dioxide (NO2)].

Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide (NO2) along with particles in the air can often be seen as a reddish-brown layer over many urban areas.

Nitrogen oxides form when fuel is burned [...]. The primary sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels.

In the atmosphere, nitrogen oxides can contribute to formation of photochemical ozone (smog) and have health consequences. They also lead to acid rain and contribute to global warming. (Source: US EPA NOx: What is it? Where does it come from?   )



The term organic has different meanings (depending on the context):

In chemistry, "organic" refers to a chemical compound based on a hydrocarbon, i.e. a chain or a ring of carbon atoms onto which hydrogen atoms are bonded.

In agriculture, "organic" refers to a production system that excludes or limits the use of chemicals


Organophosphate pesticides

A group of organic compounds containing phosphorus that are used as insecticides.

Organophosphate pesticides break down rapidly when exposed to sunlight, air, and soil, although small amounts can be detected in food and drinking water. (Source: GreenFacts )


Ozone is a form of oxygen having the molecular form of O3. It is a bluish, unstable gas with a pungent odour, found in two parts of the atmosphere: the stratosphere and the troposphere.

The ozone layer: The stratosphere contains a layer in which the concentration of ozone is greatest, the so called ozone layer. The layer extends from about 12 to 40 km. It shields the Earth from ultraviolet radiation's harmful health effects on humans and the environment. This layer is being depleted by human emissions of chlorine- and bromine-containing compounds.

Ground-level ozone: At ground level (in the troposphere), ozone is considered an air pollutant that can seriously affect the human respiratory system. It is a chemical oxidant and a major component of photochemical smog. (Source: GreenFacts)


Particulate matter

Sum of all microscopic solid and liquid particles, of human and natural origin, that remain suspended in a medium such as air for some time. These particles vary greatly in size, composition, and origin, and may be harmful.

Particulate matter may be in the form of fly ash, soot, dust, fog, fumes etc. (Source: GreenFacts)


Passive smoking

Passive smoking is defined as the involuntary inhalation of somebody else’s tobacco smoke. Such secondhand tobacco smoke is a mixture of mainstream smoke exhaled by active smokers and sidestream smoke released from the smouldering tobacco and diluted with ambient air. Usually passive smoking occurs in a closed environment, but it can also happen in an open environment. Passive smokers inhale carcinogens, as well as other toxic components, that are present in secondhand tobacco smoke. (Source: GreenFacts)


A toxic chemical product that kills harmful organisms (e.g., insecticides, fungicide, weedicides, rodenticides, acaricides). (Source: FAO Glossary of biotechnology & genetic engineering  )



Phthalates are a group of man-made chemicals that are structurally related to the organic acid, phthalic acid. The most important use of phthalates is in plastics, especially PVC, where they act as plasticisers. (Source: based on the GreenFacts Digest on phthalates)



A group or number of people living within a specified area or sharing similar characteristics (such as occupation or age). (Source: ATSDR Glossary of Terms  )


Primary & Secondary pollutant

A primary pollutant is an air pollutant emitted directly from a source.

A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

Examples of a secondary pollutant include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight; NO2, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water. (Source: GreenFacts)


A radioactive gas that is released by the breakdown of uranium, a substance found in some soils and rocks. It can get inside buildings by diffusing through the soil and can also be released from concrete.

Breathing in too much radon can damage lung cells and lead to lung cancer. (Source: GreenFacts )

Respiratory tract

The organs that are involved in breathing.

These include the nose, throat, larynx, trachea, bronchi, and lungs. Also known as the respiratory system. (Source: St. Jude Children's Research Hospital Glossary   )



Rhinitis is an inflammation of the cells lining the nose resulting from the inhalation of an allergen.

The symptoms include nasal obstruction, runny nose and sneezing. Rhinitis can be seasonal, e.g. allergy to pollen (hay fever), or [occur] all year round - e.g. allergy to animals or dust. (Source: Glossary   )

Risk assessment

A scientifically based process consisting of four steps:

  • hazard identification,
  • hazard characterization,
  • exposure assessment and
  • risk characterization
(Source:   Official Journal of the European Communities 2002 L 31 )


Route of exposure

The way people [or other living organisms] come into contact with a hazardous substance. Three routes of exposure are breathing [inhalation], eating or drinking [ingestion], or contact with the skin [dermal contact]. (Source: ATSDR Glossary of Terms  )

Scientific Committee on Health and Environmental Risks

The Scientific Committee on Health and Environmental Risks (SCHER) is one of three independent non-food scientific committees that advise the European Commission on matters of consumer safety, public health and the environment.

The committee was set up in 2004 to provide the European Commission with scientific advice on health and environmental risks. It replaced the Scientific Committee on Toxicity, Ecotoxicity and the Environment (CSTEE).

SCHER addresses questions relating to examinations of the toxicity and ecotoxicity of chemicals, biochemicals and biological compound whose use may have harmful consequences for human health and the environment.

In particular, the Committee addresses questions related to new and existing chemicals, the restriction and marketing of dangerous substances, biocides, waste, environmental contaminants, plastic and other materials used for water pipe work (e.g. new organics substances), drinking water, indoor and ambient air quality. It addresses questions relating to human exposure to mixtures of chemicals, sensitisation and identification of endocrine disrupters.

The SCHER complies with the principles of independence, transparency and confidentiality. SCHER members therefore make a declaration of commitment to act in the public interest and a declaration of interests; requests for opinions, agendas, minutes and opinions are published; work and publications are done with regard to the need for commercial confidentiality.

For further information on the SCHER see:
SCHER website 

Secondhand tobacco smoke

Secondhand tobacco smoke is the smoke inhaled by passive smokers.

It is a mixture of smoke exhaled by smokers (mainstream smoke) and smoke released from their smouldering cigarette, cigar, or other smoking device (sidestream smoke) diluted with ambient air.

Secondhand tobacco smoke contains carcinogens, as well as other toxic components. (Source: GreenFacts)

Sudden infant death syndrome

The diagnosis given for the sudden death of an infant under one year of age that remains unexplained after a complete investigation.

Because most cases of SIDS occur when a baby is sleeping in a crib, SIDS is also commonly known as crib death.

Most SIDS deaths occur when a baby is between 1 and 4 months of age. (Source: Women's Health Zone Glossary   )


Able to poison or harm an organism. Toxic substances can cause adverse health effects. (Source: GreenFacts)


The capacity or property of a substance to cause adverse effects. (Source: GreenFacts)



A toxicant produced by a living organism. (Source: IPCS )



Naturally occurring heavy metal that is denser than lead.

Uranium is radioactive and is the principal fuel of nuclear reactors. (Source: GreenFacts )


A virus is a small organism which can infect other biological organisms.

Viruses can only reproduce by invading and taking over cells as they lack the cellular machinery for self reproduction.

They cause diseases in human beings, animals, plants and bacteria.

Examples of human diseases caused by viruses include the common cold, influenza, small pox, AIDS, and cold sores. (Source: GreenFacts)


Volatile organic compound

Any organic (carbon-containing) compound that evaporates readily to the atmosphere at room temperature.

VOCs contribute significantly to smog production and certain health problems.

VOCs often have odors, examples include gasoline, alcohol, and the solvents used in paints. (Source: GreenFacts)


Vulnerability (in health science)

The likelihood of being unusually severely affected by a substance either as a result of susceptibility to the effects of these substances or as a result of a greater than average [exposure]. (Source: WHO Europe  Answers to follow-up questions from CAFE )

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