Pollutants

Fine Particles (PM₁₀ and PM_2.5)

What is Particulate Pollution?

Particulate pollution (also sometimes described as particulate matter) consists of a mixture of small particles of various materials, which are small enough to be suspended in the air. These airborne particles are measured in a number of different size fractions according to their effective size (referred to as their “median aerodynamic diameter”). Most air quality monitoring measures PM₁₀ (that is, particles with a median aerodynamic diameter of 10 micrometres or less) or PM_2.5 (particles with a median aerodynamic diameter of 2.5 micrometres or less). A micrometre, or micron, is one-thousandth of a millimetre.

Where Does Particulate Pollution Come From?

Particulate pollution is composed of a wide range of materials, both  natural and human-made, including:

• soot from combustion sources (such as road vehicle exhaust, domestic solid fuel and oil burning, and industrial combustion);
• Non-exhaust emissions from road traffic; for example dust from tyre and break wear, and suspended road dust. (As European legislation has reduced vehicle exhaust emissions over recent years, non-exhaust emissions have become more important.)
• secondary particulate matter; this means particles that aren't emitted from any source, but instead are formed by chemical reactions between other air pollutants, such as oxides of nitrogen, oxides of sulphur and ammonia. The reactions can form particles of chemical compounds such as sulphates and nitrates. Secondary particulate matter can often be transported over very large distances – on a national or continental scale.
• coarse particles and material from construction work, demolition, road work;
• suspended soils and dusts (e.g. from the Sahara Desert), sea salt, volcanic emissions and biological particles (such as pollen).

What Are Its Effects?

Fine particles in the PM₁₀ fraction are small enough to be inhaled; unlike larger particles, which get trapped naturally in our noses and throats, PM₁₀ particles can travel into our airways. There, they  can cause inflammation, and a worsening of the condition of people with heart and lung diseases. The smaller PM_2.5 particles are considered even more harmful, as they can be carried deep into the lungs. These ultrafine particles may carry surface-absorbed toxic, or carcinogenic, compounds into the body.

Particles also have a range of important non-biological impacts including:

• soiling of buildings etc.; in the past, before the Clean Air Acts of the 1950s, this problem was much worse than it is today. Many buildings in towns and cities became stained with smoke and soot; you can still see the evidence of this today, on some old buildings.
• reducing visibility (fine particles - aerosol),
• effects on atmospheric chemistry.

How Can I Avoid Exposure?

High concentrations of PM₁₀ and/or PM_2.5 can happen at different times of the year, due to various causes.

In winter, concentrations of pollutants from local emission sources can build up during periods of cold, still weather. This is because there is little wind to disperse the pollutants; it is made worse in cold weather as people may be using more fuel than usual in their homes and workplaces.

In spring and summer, ‘episodes’ of high particulate pollution are often caused by secondary particulate matter. This consists of particles of chemical compounds such as sulphates and nitrates, formed from chemical reactions in the atmosphere between other pollutants such as oxides of nitrogen, sulphur dioxide and ammonia. Secondary particulate pollution episodes may originate long distances away and may affect large areas.

Use this website to check the forecast air quality in your area. If you, or someone in your family, has a health condition which may be affected by air pollution (such as asthma or heart disease) you/they can use Air Aware to get SMS (text) air pollution alerts for Northern Ireland.

How Can I Help?

As for NO_x, one of the most important is road vehicles. Try to drive less, if you can: it may be possible to walk, cycle or use public transport, especially for short journeys. NIDirect’s web page on Active Travel and Sustainable Transport (https://www.nidirect.gov.uk/information-and-services/travel-transport-and-roads/active-travel-and-sustainable-transport) provides advice on how to do this conveniently and safely.

Many people still need to drive – especially if they are less mobile or live in a rural area; check out NIDirect’s tips on Greener Driving, at https://www.nidirect.gov.uk/information-and-services/active-travel-and-sustainable-transport/greener-driving.

If you use solid fuels for heating, check before buying that the fuel is of an approved type for your area. Keep warm at home, but don’t waste fuel: 21°C is comfortable for most people.

If you have a wood burning stove or open fire, follow Defra’s advice on domestic burning, here: https://consult.defra.gov.uk/airquality/domestic-burning-of-wood-and-coal/supporting_documents/open%20fires%20wood%20burning%20stoves%20%20guideA4update12Oct.pdf

Avoid lighting barbecues in very hot, still summer weather, or bonfires in cold, still winter weather.

Ozone

What is Ozone?

Ozone is a gas; it is a form of oxygen – but while ordinary oxygen molecules consist of two oxygen atoms bound together (chemical formula O₂), each molecule of ozone consists of three atoms of ozone joined together (chemical formula O₃).

Ozone is found naturally in our atmosphere. High up in the atmosphere, ozone is essential. A layer of air containing high concentrations of ozone (the ozone layer) protects all life on earth from the sun’s harmful ultraviolet rays. At ground level however, it's harmful to breathe and can make breathing difficult, especially for people with asthma. Ozone often contributes to poor air quality in the summer.

Where Does Ground-Level Ozone Come From?

Ozone is not emitted directly from any man-made source in any significant quantities. In the lower atmosphere, O₃ is mostly formed by a complex series of chemical reactions, initiated by sunlight and accelerated by high temperatures. These chemical reactions need three things:  

• Volatile organic compounds (VOCs) – another group of pollutants. The sources of VOCs are similar to those described for NO_x above, but also include other activities such as solvent use, and petrol distribution and handling.
• Nitrogen oxides (NO_x)
• Sunlight.

The chemical reactions which produce ozone do not take place instantly, but can take hours or days. As a result, ozone measured at a particular location may have arisen from VOC and NO_x emissions many hundreds or even thousands of miles away. Maximum concentrations, therefore, generally occur some distance downwind of the original sources of precursor emissions – often in rural areas rather than in towns and cities.

What Are Its Effects?

Ozone has a wide range of health and ecosystem impacts. It irritates the eyes and the airways of the lungs, increasing the symptoms of those suffering from asthma and lung diseases. When ozone concentrations are very high, hospital admissions for respiratory problems increase. Even healthy people may notice symptoms such as irritated eyes or a tickly throat, especially if they are doing exercise outdoors, such as running. In addition to its serious impacts on human health, ozone is also harmful  to many plants, including trees and  crops. It can also damage or age some human-made materials, as well as bleaching paints and fabrics.

How Can I Avoid Exposure?

As explained above, ozone concentrations are usually highest on warm sunny days, especially in rural areas. Because of the way ozone is formed, concentrations tend to build up throughout the day, peaking in the late afternoon. On summer days it may be best to do any vigorous exercise – such as going for a run or a cycle ride – early in the morning or later in the evening.

How Can I Help?

Ozone is a ‘transboundary’ pollutant, so it is difficult to control at a local level. However, because the formation of ozone involves oxides of nitrogen and volatile organic compounds, anything you can do reduce emissions of these pollutants will help reduce ozone formation.   

Sulphur Dioxide

What Is Sulphur Dioxide?

Sulphur dioxide (chemical formula SO₂) is a gaseous pollutant. Each molecule of SO₂ consists of one atom of sulphur (sometimes spelt ‘sulfur’) and two of oxygen.

Where Does Sulphur Dioxide Come From?

SO₂ is produced when a fuel or other material containing sulphur is burned. Globally, much of the sulphur dioxide in the atmosphere comes from natural sources such as volcanoes; however,  in the UK, the most important source is the energy industry, followed by residential, institutional and commercial fuel use. The fuels which give rise to most SO₂ are coal and heavy fuel oils.

Areas where there is widespread domestic use of coal or oil for heating can have higher local concentrations of SO₂. Historically, this was the case in parts of Northern Ireland: however, SO₂ concentrations have greatly reduced over recent decades, as the availability of natural gas has increased in the region, reducing the need to use coal and oil. No exceedances of applicable limit values or objectives for SO₂ have been measured in Northern Ireland since 2001.  

What Are Its Effects?

SO₂ is one of the chemical compounds that gives coal smoke its distinctive, eye-watering smell. It is a respiratory irritant that can cause the airways to constrict: people with asthma are likely to be particularly sensitive to it. SO₂ is considered more harmful when concentrations of particles and other pollutants are also high. This is a good example of combined or synergistic effects of air pollutants.

SO₂ is also damaging to the environment; it contributes to acid rain, and can also react with other pollutants to form fine particulate matter.

How Can I Avoid Exposure?

You’re most likely to encounter sulphur dioxide pollution in residential areas where there is a high usage of oil and solid fuels for heating.  It may be part of a winter pollution episode, together with PM₁₀ and NO₂. Be aware of current and forecast pollution levels: why not try the Air Aware text messaging service (https://www.nidirect.gov.uk/articles/air-pollution-and-health )?

How Can I Help?

If you use solid fuels for heating, check before buying that the fuel is of an approved type for your area. If your house has an oil-fuelled boiler, get it serviced regularly, so that it operates efficiently and uses no more fuel than necessary. Keep warm at home, but don’t waste fuel: 21°C is comfortable for most people.

Ammonia

Ammonia (chemical formula NH₃) is a gas that is mostly released into the air by farm activities. These include the use of fertilisers, and also farm animals and the wastes they produce. In 2017, 87% of the UK’s ammonia emissions came from agriculture. Ammonia contributes to air pollution because it can react with other pollutants (the oxides of nitrogen and sulphur) to produce fine particles of ammonium nitrate and ammonium sulphate. On some days, especially in spring and summer, a substantial proportion of the particulate pollution (PM₁₀ and PM_2.5) is made up of this type of particulate matter.

How Can I Avoid Exposure?

Concentrations of ammonia in our outdoor air are not usually high enough to cause any health effects on their own. The main human health concern from ambient ammonia is its role in the formation of secondary particulate matter. Please see the advice above for fine particles.

How Can I Help?

Farming is an important livelihood for many people in Northern Ireland; farmland is also an important habitat for many species of plants and animals, and part of the unique landscape of Northern Ireland.

Our farmers work hard to produce the food we buy, and they understand the importance of protecting our countryside. It’s therefore important that we continue to support them. Some ways we can do this are:

• To buy locally-farmed produce when we can. (This also helps cut down on pollution caused by transporting food long distances).
• Look for labels that show the food has been produced with respect for the environment.
• To help our farmers avoid unnecessary ammonia emissions, try to use all the food you buy, and minimise waste. The ‘Love Food Hate Waste’ website (https://lovefoodhatewaste.com/) has plenty of advice on how to do this safely.

Carbon monoxide

What Is Carbon Monoxide?

Carbon monoxide (CO) is a colourless, odourless poisonous gas. Each molecule of CO consists of one atom of carbon and one of oxygen.

How Is Carbon Monoxide Formed?

CO is produced when a fuel containing carbon is burned, without sufficient oxygen to complete the combustion process and turn it into carbon dioxide (CO2). This can happen in many situations, including petrol vehicle engines, industrial processes and domestic heating systems. The importance of petrol engines as a source has decreased in recent decades, and the most important source is now residential fuel use (source: National Atmospheric Emissions Inventory, http://naei.beis.gov.uk/overview/pollutants?pollutant_id=4).

What Are Its Effects?

This gas prevents the normal transport of oxygen by the blood. In high enough concentrations, this can lead to a significant reduction in the supply of oxygen to the heart, particularly in people suffering from heart disease.

How Can I Avoid Exposure?

Although carbon monoxide is very poisonous, levels of this gas in outdoor air are usually too low to be harmful to healthy people. People are usually only likely to be in danger from carbon monoxide indoors, if they have a faulty heating appliance.  CO is also a harmful constituent of cigarette smoke.

Benzene

What is Benzene, and Where Does it Come From?

Benzene (chemical formula C₆H₆) is a Volatile Organic Compound (VOC). It is a minor constituent of petrol. The main source of benzene in the atmosphere in Europe is the distribution and combustion of petrol. Combustion by petrol vehicles is the single biggest source.

What Are Its Effects?

Benzene is known to be carcinogenic (causes cancer) in humans. Other potential  health effects of benzene include  central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.

How Can I Avoid Exposure?

Concentrations are usually highest where there is a lot of traffic; beside major roads in cities.

What Can I do?

If you have a petrol car, avoid unnecessary journeys – the use of petrol is an important source of benzene. When filling your car with petrol, try to avoid spills.

1,3-Butadiene

What is 1,3-Butadiene, and Where Does it Come From?

1,3-butadiene, like benzene, is a Volatile Organic Compound (VOC) emitted into the atmosphere principally from fuel combustion in petrol and diesel vehicles. 1,3-butadiene is also an important chemical in certain industrial processes, particularly the manufacture of synthetic rubber.

What Are Its Effects?

Possible chronic health effects from 1,3-butadiene include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.

How Can I Avoid Exposure?

Concentrations are usually highest where there is a lot of traffic; beside major roads in cities.

What Can I do?

As for benzene, if you drive a petrol or diesel car, avoid unnecessary journeys. When fuelling your car, try to avoid spills.

Lead and Other Metallic Pollutants

What are These Pollutants and Where Do they Come From?

Concentrations of several toxic metals and other elements - lead, arsenic, cadmium and nickel – are also covered by UK and EU legislation. Today, these pollutants are mostly produced by industry. Since the introduction of unleaded petrol in the UK there has been a significant reduction in urban lead levels in particular.

What Are Their Effects?

Lead, arsenic, cadmium and nickel are all toxic, and short-term or long-term exposure can affect human health in a number of ways. To find out more about these, please see the “Overview of Air Pollutants” pages on the National Atmospheric Emissions Inventory website (http://naei.beis.gov.uk/overview/ap-overview)