Box ES.1. The main air pollutants and their effects on human health and the environment

Sulphur dioxide (SO2)

Sulphur dioxide is emitted when fuels containing sulphur are burned. It contributes to acid deposition, the impacts of which can be significant, including adverse effects on aquatic ecosystems in rivers and lakes, and damage to forests.

Nitrogen oxides (NOX)

Nitrogen oxides are emitted during fuel combustion, such as by industrial facilities and the road transport sector. As with SO2, NOX contributes to acid deposition but also to eutrophication. Of the chemical species that comprise NOX, it is NO2 that is associated with adverse affects on health, as high concentrations cause inflammation of the airways and reduced lung function. NOX also contributes to the formation of secondary inorganic particulate matter and tropospheric (ground-level) ozone.

Ammonia (NH3)

Ammonia, like NOX, contributes to both eutrophication and acidification. The vast majority of NH3 emissions — around 94% in Europe — come from the agricultural sector, from activities such as manure storage, slurry spreading and the use of synthetic nitrogenous fertilisers.

Non-methane volatile organic compounds (NMVOCs)

NMVOCs, important O3 precursors, are emitted from a large number of sources including paint application, road transport, dry-cleaning and other solvent uses. Certain NMVOC species, such as benzene (C6H6) and 1,3-butadiene, are directly hazardous to human health. Biogenic NMVOCs are emitted by vegetation, with amounts dependent on the species and on temperature.

Particulate matter (PM)

In terms of potential to harm human health, PM is one of the most important pollutants as it penetrates into sensitive regions of the respiratory system. PM is emitted from many sources and is a complex heterogeneous mixture comprising both primary and secondary PM; primary PM is the fraction of PM that is emitted directly into the atmosphere, whereas secondary PM forms in the atmosphere following the oxidation and transformation of precursor gases (mainly SO2, NOX, NH3 and some volatile organic compounds (VOCs)). References to PM in this report refer to primary PM.

Carbon monoxide (CO)

Carbon monoxide is produced as a result of fuel combustion. The road transport sector, businesses and households, and industry are important sources. Long-term exposure to low concentrations of CO can result in neurological problems and potential harm to unborn babies. Carbon monoxide can react with other pollutants to produce ground level ozone. Elevated levels of ozone can cause respiratory health problems and can lead to premature mortality.

Polycyclic aromatic hydrocarbons (PAHs)/Benzo(a)pyrene (BaP)

Polycyclic aromatic hydrocarbons are a large group of persistent organic pollutants (POPs) which contribute to different harmful effects in the environment and to human health. PAHs are released by combustion processes, as well as being emitted via evaporation from materials treated with creosote, mineral oils, pitch etc. BaP is a specific PAH formed mainly from the burning of organic material such as wood, and from car exhaust fumes especially from diesel vehicles. It is a known cancer-causing agent in humans. In Europe, BaP pollution is mainly a problem in certain areas such as western Poland, the Czech Republic and Austria where domestic coal and wood burning is common.

Dioxins and furans (PCCD/F)

PCDDs and PCDFs are formed by the combustion of fuels and wastes, processing of metals and the production of pulp and paper. Exposure to normal background levels of dioxins and furans is unlikely to cause health problems, although some PCDDs and PCDFs may cause cancer and may affect the unborn child in low concentrations. PCDDs and PCDFs are categorised as POPS, being persistent in the environment. Emissions to air will eventually be deposited on soil and/or waters. Livestock and wildlife can subsequently ingest them from soil and vegetation, with fish susceptible to uptake from aquatic sediments.

Polychlorinated biphenyls (PCBs)

Polychlorinated biphenyls are used mainly as electrical insulating material in capacitors and transformers. They have also been used as flame retardants. The main source of releases have been from their manufacture and use, as well as during disposal of PCB containing equipment. PCBs may cause cancer and can affect the unborn child. PCBs are toxic to wildlife, particularly aquatic organisms. They can cause serious reproductive and developmental problems and damage to the immune system. PCBs are categorised as a persistent organic pollutant (POP).

Hexachlorobenzene (HCB)

Hexachlorobenzene was used as a fungicide on seeds (now banned), and is also used in the manufacture of chlorinated organic solvents. It is released to the environment as a byproduct of the burning of coal, waste incineration and some metal processes. It has also been released through its use as a fungicide. The environment levels of HCB are not typically high enough to cause significant health effects. HCB is however classed as dangerous to the environment. The main concern over environmental releases is related to its persistence and ability to bio-accumulate in the food chain. High levels can build up in fish and marine mammals and also certain plants.

Hexachlorocyclohexane (HCH)

Hexachlorocyclohexane is a family of organic compounds, the most common of which is gamma-HCH (lindane). The main use of lindane has been as a timber insecticicide. Releases of lindane to water damage insects and fish. It also accumulates in fish. Its ability to persist and accumulate in the environment mean that lindane can travel long distances and have effects far from the point of emission. Emissions of HCH occur through its manufacture, use, storage and transport.

Heavy metals

The heavy metals arsenic (As), cadmium (Cd), lead (Pb), mercury (Hg) and nickel (Ni) are emitted mainly as a result of various combustion processes and industrial activities. Both BaP and heavy metals can reside in or be attached to PM. As well as polluting the air, heavy metals can be deposited on terrestrial or water surfaces and subsequently build up in soils or sediments. Heavy metals are persistent in the environment and may bio-accumulate in food-chains.