Outdoor air pollution

The term ‘air pollution’ is used in different ways by different people. Here we use it to cover man-made pollutants in the outdoor air. This page explains outdoor air pollution and its effects on the lungs.

In the past, the main source of air pollution in the UK was the burning of fossil fuels, such as coal, in homes and factories.

This produced high levels of smoke and sulphur dioxide. However, following the Clean Air Acts brought in during the last century, this has greatly improved.

These days, the major problem is petrol and diesel motor vehicles, which emit a variety of pollutants.

The most troublesome of these are:

  • oxides of nitrogen;
  • particles;
  • volatile organic compounds; and
  • carbon monoxide

This type of pollution also increases ground levels of ozone.

This page does not cover other sorts of man-made pollution, such as that from waste incinerators or composting sites. The evidence that these are harmful in low concentrations to people with lung diseases is uncertain and remains the subject of research studies.

Types of air pollution

Air pollutants are usually present in a mixture. Some – such as the smoke from the back of a badly tuned car – are visible but most are not and, at normal levels, they do not have a smell.
Important types of air pollution include:

Oxides of nitrogen (NOx) – in particular nitrogen dioxide (NO2)

These are produced mainly from motor vehicles (cars, lorries and buses) and levels are highest where traffic is busiest.

Very high levels of NOx can irritate the lining of the airways and cause a cough and difficulty breathing. However, such high levels are rarely found in outdoor air in the UK.

Particles (‘particulate matter’ or ‘PM’)

Particles are produced mainly from diesel engines but also from industrial sources and from burning coal and other fossil fuels.

If they are small enough, they can be breathed into the lungs. It is believed that the smallest particles (‘particulates’) are the most hazardous. At high levels they can make breathing problems worse. They can also cause heart attacks and strokes in vulnerable people.

Volatile organic compounds (VOC)

Motor vehicle fuel contains a number of chemicals that can get into the air; the most important of these is benzene. At high levels over many years, benzene can cause cancer.

Carbon monoxide

The biggest personal exposure to carbon monoxide comes from cigarette smoking. In the outdoor air, carbon monoxide comes mainly from traffic exhaust.

High levels of carbon monoxide interfere with the carriage of oxygen in the blood. This does not lead to breathlessness but can be a problem for people with heart and lung diseases.

Ozone

Ozone is a ‘secondary’ pollutant because, unlike the others, it is not produced directly by traffic but by a ‘photochemical’ reaction of sunlight on NOx.

Levels of ozone tend to be highest in the summer and are often higher in the country than in towns. They are the chief cause of ‘summer smogs’.

High levels of ozone are irritating to the airways of completely healthy people and people with all sorts of lung diseases. For those with a lung disease high levels of ozone can cause a cough and difficulty breathing.

Air pollution in the UK

In comparison to many other countries, air pollution levels in the UK are low, although in parts of major cities they are high enough to be of concern.

With changes in manufacturing and power generation over the past 50 years industrial and domestic emissions have greatly improved. However, traffic pollution has become worse and is now the major threat to lung health.

The highest levels of air pollution in the UK are usually found in cities, particularly near busy roads. In contrast, levels of ozone tend to be higher in rural areas.

The weather has a major impact on air pollution. For example, certain conditions can cause a ‘temperature inversion’ when the air near the earth’s surface is cooler than that above, trapping pollutants close to the ground.

The UK has a wide network of sites that monitor levels of air pollution. The information from them is available to the public. See below for details of where to find this information.

Air pollution and lung health

The health problems from air pollution are both long-term and short-term.

Long-term health problems arise from breathing polluted air over several years. Studies of large populations suggest that this can, by small amounts, increase the risk of lung cancer and reduce the rate at which children’s lungs grow.
The evidence that it may increase the risk of developing asthma is uncertain, although it may prompt attacks of asthma or make the condition worse.

It may also prompt attacks of COPD (chronic obstructive pulmonary disease) – an umbrella term for chronic bronchitis and emphysema – or make the condition worse.

Short-term problems arise when air pollution levels are high for a short period of time. At high levels, most of the pollutants are irritating to the airways and can cause a cough and shortness of breath, especially in people with lung diseases such as asthma or COPD.

People react to high levels of air pollution in different ways and some are more affected than others. Vulnerable people are those who have diseases such as asthma or COPD, and especially older people.

Older people with heart disease are also vulnerable. However, not all vulnerable people will have problems with air pollution.

What should I do when levels of air pollution are high?

Air pollution in the UK does not rise to levels at which people need to make major changes to their habits to avoid exposure; for example, nobody need fear going outdoors.

Children should not be kept from going to school or stopped from taking part in games.

When levels of air pollution are high, adults with COPD and both children and adults with asthma should:

  • consider reducing or avoiding strenuous, outdoor exercise;
  • try to avoid exercise in highly polluted areas such as main roads; and
  • make sure that, if they use one, they carry their reliever inhaler with them.

The use of masks is not recommended; they are often ineffective and may make breathing more difficult.

How can we prevent air pollution?

The most important source of air pollution in the UK is now motor vehicles. We all have a responsibility to choose methods of transport with this in mind. Where possible walk, bicycle, or use public transport. In line with European and international agreements, the UK government aims to reduce levels of air pollution from all sources.

How can I find out more?

These websites contain useful information on air pollution in the UK or Europe:

You can also subscribe, for free, to 24-hour forecasts of air pollution in your area, emailed to you, as well as monthly summaries of the latest air pollution news and reports:

For more advice and information about the effects of air pollution, call the BLF Helpline on 03000 030 555. Lines are open Monday to Friday, 10am-6pm and calls are charged at a local rate.

This page covers man-made pollutants in the outdoor air. The BLF also produces other information that may be useful to you.

The BLF values feedback on all of its information. To let us know your views, please contact us.

Code: FL5
Last medically reviewed: October 2011
Due for medical review: October 2013
For references call 020 7688 5555