Particulate matter

Particulate matter consists of very small particles which can be solid or liquid. Some of these particles occur naturally, and many are man-made. Particulate matter is usually referred to as PM with a number after it to show how small the PM is. The EPA monitors two types of PM and compares levels to limit values in the CAFE (Cleaner Air for Europe) Directive and WHO guidelines. These are PM10 and PM2.5.

PM10 means that the particulate matter is 10 microns or less in diameter, small enough so you could lay 10 of these particles across the width of an average human hair. PM2.5 signifies that it is particulate matter of 2.5 microns or less in diameter – you could lay 40 of these particles across the width of an average human hair.

Fine particulate matter

PM2.5 is also known as 'fine particulate matter'. This is the most important pollutant in Ireland from a health perspective. It is estimated to cause ~1,300 premature deaths in Ireland annually.

What is fine particulate matter?

Fine particulate matter (PM2.5) is made of very small particles of solids or liquids that are small enough to pass through the lungs and into the blood stream causing health impacts such as cardiopulmonary disorders, respiratory disorders and stoke.

What are the sources of fine particulate matter in Ireland?

The main source of fine particulate matter in Ireland is from the burning of solid fuel to heat homes. Burning solid fuel in stoves and especially in open fires is an inefficient process – not all the solid fuel is fully burned. These unburnt particles leave the fireplace or stove by the chimney, or directly into the room they are heating. This pollution is then breathed in by you and your family or by those in your locality, leading to health effects.

Bituminous (Smoky) Coal

The burning of bituminous coal (sometimes referred to as “smoky coal”) has long been associated with the development of smog, especially during winter. Smog, consisting of a variety of chemicals and particulate matter, e.g. smoke, ash has been strongly attributed to the onset of some respiratory illnesses and associated diseases.

Particularly vulnerable are those suffering from ailments such as asthma many of whom are children. When burned, bituminous coal releases a considerable range of pollutants into the air including large amounts of fine particulate matter.

Nitrogen oxides

Nitrogen oxides – or NOX – are the gases nitrogen oxide (NO) and nitrogen dioxide (NO2). Both of these are pollutants that are emitted in ambient air when petrol or diesel is burned in internal combustion engines. NO2 is more important from an ambient air quality perspective due to its increased impact on health

What are the main sources of NO2 in Ireland?

In terms of ambient air quality, the main source of NO2 in Ireland is from road transport. Diesel engine vehicles produce more NO2 than petrol vehicles. Other sources of NO2 in Ireland include:

  • off-road machinery (for example, earth movers and lawnmowers),
  • industrial and construction activities, and
  • electricity and heat production equipment such as central heating boilers and generators.


Ozone is a highly reactive gas which is crucial for life on earth as it's presence in the upper-atmosphere (stratosphere) shields the earth from harmful UV light from the sun. However, when ozone is present in the lower-atmosphere (troposphere) it is a harmful pollutant. Ozone air pollution is known as ground level ozone.

What is ground level ozone?

Ground level ozone is a pollutant formed in urban areas when you have car exhaust emissions mixing together and undergoing chemical reactions in sunny weather. Ground level ozone can be bad for your health.

What are the main sources of ground level ozone in Ireland?

Normally, ozone is a ‘transboundary’ pollutant in Ireland – this means that the sources of the ozone are outside Ireland (normally mainland Europe). Then, the pollutants are carried in an air mass across the sea to impact here. There is also a natural component to the ozone normally measured in Ireland. However, when weather conditions are suitable – namely dry, hot, sunny weather – then ozone can be produced by reactions of NOx and other emissions from car exhausts to produce a brown, hazy atmosphere which is called ‘photochemical smog’.

Polycyclic aromatic hydrocarbons (PAH)

PAH are chemical compounds which consist of two or more fused aromatic rings made entirely from carbon and hydrogen.

Short-term exposure to high levels of PAHs may cause eye irritation, nausea, diarrhoea, vomiting and confusion, although high concentrations are unlikely to be found in ambient air. The chronic or long-term effects of exposure to low levels of PAHs may include cataracts, kidney and liver damage and jaundice. Many PAHs have also been identified as carcinogenic with airborne PAHs most likely to cause lung cancer. PAHs are monitored in Ireland as part of a PM10 fraction by using Benzo(a)Pyrene (BaP) as a marker for all PAHs.

What are the sources of PAH in Ireland?

PAH are emitted domestically from the combustion of solid fuels, such as coal, wood and peat. They can also be emitted from incomplete combustion of fuel in vehicles. Waste burning or ‘backyard burning’ and bonfires are a source of PAH as is cigarette smoke.