Air Pollution
Clean Air for Kids


Acid deposition
Acidic air pollution that falls to the ground as either particles (dry deposition), or solutions in rain (wet deposition). The latter is commonly known as "acid rain". Produced from the atmospheric build-up of NOx and SO2.

Air pollution
A term used to describe any unwanted chemicals or other materials that contaminate the air that we breathe resulting in the degradation of air quality.

Ammonia (NH3)
A gas consisting of molecules of nitrogen (1) and hydrogen (3) atoms produced during the manufacture of fertilisers, it is colourless but has a very strong smell.


Heat resistant mineral. Once used for insulation but now known to cause cancer.

A disease that makes it difficult for a person to breathe, especially during exercise.

The envelope of gases which surrounds the Earth.

Bed rock
The solid unweathered rock that lies beneath loose surface deposits.

The ability to withstand an increase in acid deposition, without changing pH.

Carbon monoxide (CO)
A highly poisonous gas, consisting of molecules of carbon (1) and oxygen (1) atoms, produced when fuel is burnt during incomplete combustion. It is emitted mainly from car exhausts.

The term applied to a cancer-causing substance.

Catalytic converter
A device fitted to the exhaust system of a vehicle, which converts the majority of harmful exhaust pollutants, such as hydrocarbons, into less harmful ones.

An area of land drained by a river and its tributaries (streams etc.).

Clean Air Acts
Acts passed in1956 and 1968 to reduce the amount of pollution from industries and homes in the UK.

Burning, e.g. of fossil fuels or biomass.

A measure of the atmospheric content of a gas, defined in terms of the proportion of the total volume that it accounts for. Trace gases in the atmosphere are usually measured in parts per million by volume (ppmv), parts per billion by volume (ppbv) or parts per trillion (million million) by volume (pptv).

A process in which a solid is dissolved and changed by the action of a chemical.

Critical load
The maximum amount of deposition that a defined environment can withstand, without suffering long term damage.

Diffusion tubes
Tubes used to measure the amount of a particular pollutant in the atmosphere, usually oxides of nitrogen.

Poisonous chemical by-products from the manufacture of certain herbicides and bactericides.

The scattering and distribution of pollutants in the atmosphere.

Dust mites
Tiny, eight-legged creatures relating to spiders and ticks that can cause human allergies.

A system of interconnected habitats and their species of flora (plants) and fauna (animals), usually defined by a specific geographical area and/or climatic regime, e.g. mountain, polar, forest ecosystems.

The discharge of waste gases into the atmosphere.

Emissions inventory
Information concerning the distribution of pollution sources in a certain area, and the amount and types of pollutants being emitted.

Energy efficiency
Quantitatively, the more energy that can be produced per unit mass of fuel, the more efficient is the energy production. The efficiency with which energy is utilised can be increased by both improving energy supply technology and managing energy demand more effectively.

Expert Panel on Air Quality Standards. EPAQS provides advice and guidance to the UK Government on air quality.

Flue-gas desulphurisation (FGD)
A process that removes sulphur dioxide after fuel combustion before being emitted to the atmosphere.

Fluidised bed combustion (FBC)
A process that removes sulphur dioxide during fuel combustion before being emitted to the atmosphere.

A colourless gas with a strong smell. Used in making resins.

Fossil fuel
Any hydrocarbon deposit that can be burned for heat or power such as coal, oil or natural gas. Fossil fuels are formed from the decomposition of ancient animal and plant remains.

Relating to the stomach and intestinal tract.

Global warming
A continued warming of the Earth's surface and lower atmosphere (troposphere) as a result of pollution by man.

A coarse grained igneous rock consisting of quartz, feldspar and mica.

A constituent of red blood cells, which facilitates the absorption of oxygen into the bloodstream for respiration.

A measure of the amount of water vapour in the air.

Organic compounds containing carbon and hydrogen.

A substance that is toxic to the immune system.

Industrial Revolution
The rapid growth of industry which began in the late 18th century, made possible by the harnessing of energy from fossil fuels.

A toxic blue/white metal emitted as particles by vehicles using leaded petrol. Lead toxicity in the body can lead to the impairment of intelligence, particularly in children.

A form of cancer where too many white blood cells are formed.

Megawatt (MW)
One million watts.

Micrograms per cubic metre.

Micron (µm)
One millionth of a metre.

Fungi that cause organic matter to decay.

National Air Quality Strategy (NAQS)
A national programme to monitor and manage air pollution levels and air quality in the UK. Published in spring 1997 following the Environment Act of 1995.

Nitrogen oxides (NOx)
The collective term for nitric oxide (NO) and nitrogen dioxide (NO2).

Ozone (O3)
A gas formed when nitrogen oxides and hydrocarbons react in the presence of sunlight. Consequently, it is known as a secondary pollutant.

Coarse and fine particles of organic or inorganic substances present in the atmosphere.

Particulate matter (PM10)
Particles of organic or inorganic substances present in the atmosphere that are less than 10 microns (µm) in diameter.

Parts per billion.

Parts per million.

Parts per trillion.

A measure of acidity. pH 7 is neutral, values lower than 7 are acidic whilst values higher that 7 are alkaline. The scale is logarithmic so that pH 5 is 10 times as acidic as pH 6.

Photochemical smog
Describes the hazy conditions that occur when air pollutants are trapped at ground level. High levels of ozone may be produced as nitrogen oxides and hydrocarbons react in the presence of sunlight. Pollution concentrations may become very high and the air quality may be classed as 'poor' or 'very poor'. In summertime, they usually occur on warm, still, sunny days. In winter, smogs may occur on cold, calm days when air pollutants are trapped in urban areas by a layer of colder air above.

A chemical reaction involving sunlight in which molecules are split into their constituent atoms. Also known as photodissociation.

The process by which green plants use light to synthesise organic compounds from carbon dioxide and water. In the process oxygen and water are released.

Strictly too much of any substance in the wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution may be defined as 'the presence of substances in the atmosphere, resulting from man-made activities or from natural processes, causing adverse effects to man and the environment'.

The process by which animals use up stored foods (by combustion with oxygen) to produce energy.

A radioactive gas given off by certain rocks and soil.

A layer in the atmosphere above the troposphere extending upwards to about 50km. The stratosphere contains much of the total atmospheric ozone. The temperature in this region increases with height and can exceed 0oC in the summer. The air density here is much less than in the troposphere. It is not thought that the stratosphere has much influence on the weather on the Earth's surface.

Sulphur dioxide (SO2)
A colourless gas, consisting of molecules of sulphur (1) and oxygen (2) atoms, which is given off during fossil fuel combustion.

Sulphuric acid
An acid produced when sulphur dioxide dissolves in water. A component of "acid rain".

Sustainable development
Development which meets the needs of the present without compromising the ability of future generations to meet their own needs. Sustainable development tries to reconcile the needs of social and economic development with ecological conservation and environmental protection.

Pollution consisting of smoke and sulphur dioxide trapped at ground level. It usually occurs on cold, calm winter days. The term smog was derived from smoke and fog.

A term used to describe the movement of air pollution emitted in one country that crosses national boundaries to affect other countries.

The lowest layer of the atmosphere. The altitude of the troposphere varies with latitude, from about 16km at the equator to only 8km at the poles. Normally there is a decrease in temperature with height. This layer contains 75% of the total gaseous mass of the atmosphere and virtually all the water vapour and aerosols. This zone is responsible for most of the weather phenomena experienced and where atmospheric turbulence is most marked.

Volatile organic compounds
Organic air pollutants which can help to form ozone. Emission sources include vehicle exhausts, smoking and building materials.

A unit of energy output per unit time (Joules per second). Watts per square metre (Wm-2) is a measure of the energy output per unit area (e.g. the amount of solar energy received at the Earth's surface).

World Health Organisation (WHO)
WHO recommend guide values for particular pollutants, which are considered safe for human health.