Air Pollution

Air pollution is the introduction of any substance into the atmosphere that can cause harm to humans, or any other living organism, or to the surrounding environment. Air pollutants can occur in solid, liquid or gaseous form. They come from a very wide range of sources. Some, like transportation, industrial processes and cooking, relate to human activity. But natural processes, like the release of pollen grains and fungal spores, can also cause air pollution. The latter might not usually be considered as polluting but for people with hay fever and other allergies, allergens can be considered as pollutants.

The United States Environmental Protection Agency considers the following as the major air pollutants:

• Particulate matter
• Ozone
• Carbon monoxide
• Nitrogen oxides
• Sulphur dioxide 
• Lead 

According to the World Health Organisation (WHO), air pollution is responsible for an estimated 2.4 million deaths every year. The average adult breathes 3000 gallons of air every day and maybe inhaling a cocktail of different particulate and gaseous pollutants, most of them invisible. Air pollution occurs both outdoors and indoors and causes a range of health problems, including asthma attacks, heart disease and lung disease. It has also been linked to lung cancer.

Particulate matter is a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. According to the World Health Organisation, particulate matter affects more people than any other pollutant. It is present in the air year-round. There are three classes of particulate matter:

1. PM10 – particles with a diameter of 10 microns or less but greater than 2.5 microns. Also known as coarse particles, PM10 is found near roadways and in dusty industrial settings.
2. PM2.5 – particles with a diameter of 2.5 microns or less. Also known as fine particles, PM2.5 is emitted into the air from sources such as fires or may form in emissions from vehicles, power plants or heavy industry. PM2.5 is a major cause of reduced visibility (haze) occurring in polluted environments.
3. Ultrafine particles – particles with a diameter of 0.1 microns or less, and therefore on the nanoscale. There is a multitude of sources of ultrafine particles, including smoke, volcanic lava, ocean spray, vehicle exhausts, cooking, and office equipment including laser printers, photocopiers and fax machines.

PM2.5 is more harmful to health than PM10 because these smaller particles can be inhaled deeper into the lungs. Ultrafine particles may be more harmful still, although less research has been carried out on this category of the particle. Particles with diameters larger than 10 microns tend to settle, rather than remaining airborne and so are not inhaled. Fine and ultrafine particles can remain suspended in the air and may travel through great distances.

Diesel exhaust is probably the major source of outdoor particulate matter, emitting particles ranging in size from 1 - 10 microns, while coal and tobacco smoke contain very small particles, down to just 0.1 microns in size. Pollution from diesel exhaust is a problem in city centres and near busy roads used by Lorries and vans. Diesel is oily and when it burns it produces particulate matter consisting of carbon flakes coated with chemicals derived from incomplete combustion of the fuel.

O3 - Ozone
Ground-level ozone is produced by chemical reactions occurring between nitrogen oxides and Volatile Organic Compounds (VOCs) from car exhaust fumes, industrial emissions and other sources in the presence of sunlight. Ozone is a highly reactive form of oxygen and a powerful pollutant. This so-called ground-level ozone differs from the ozone layer which is found in the stratosphere and is protective against the harmful effects of sunlight. Ground ozone levels in the air tend to peak in the late afternoon and early evening. The highest levels of ozone tend to occur in the summertime and on sunny days. Ground-level ozone is the major component of smog. To find out more visit our Ozone Information Page.

Co2 - Carbon monoxide
A colourless, odourless gas. Carbon monoxide is emitted by combustion processes, outdoors by vehicles and indoors by poorly installed and maintained heating systems, gas stoves and water heaters.

NOx - Nitrogen oxides
This is the name given to a group of highly reactive gases comprising nitrogen dioxide, nitrous acid, and nitric acid. The exhausts of cars, trucks and buses are the major source of NOx pollution.

SO2 - Sulphur dioxide
An acidic gas, sulphur dioxide is emitted from fossil fuel power stations and other industrial facilities.

Pb - Lead
The main source of lead pollution used to be car exhausts, but that has stopped thanks to lead-free petrol. Today lead pollution is found around lead smelters. Other sources include metal processing and certain aircraft still using leaded fuel.

The size of the particulate in air pollution matter is related to its health risk. The smaller the particle, the easier it is for it to get into the lungs and even the bloodstream. People with heart and lung disease, children and older adults are most vulnerable to the health impact of particulate matters; there is a link with premature death in those with heart and lung disease. Chronic exposure to particulate matter contributes to the risk of developing cardiovascular and respiratory disease, and of lung cancer. In less developed countries, where indoor wood burning stoves are common, particulate matter from combustion increases the risk of acute lower respiratory infection and associated mortality among young children. It is also a risk factor for Chronic Obstructive Pulmonary Disease. Mortality in cities with high levels of pollution exceeds that in cleaner cities by 15-20%.

Particulate matter aggravates asthma symptoms, decreases lung function, and causes a general increase in respiratory symptoms like coughing and breathlessness. Exposure to particulate matter is also linked to irregular heartbeat and non-fatal heart attacks.

Ozone
Exposure to ozone can trigger asthma, reduce lung function, and cause breathing problems. Studies have shown that daily mortality goes up by 0.3% and that for heart disease by 0.4% per 10 micrograms/cubic metre increase in ozone exposure. Repeated exposure may cause permanent lung damage.

Carbon monoxide
This gas interferes with the transport of oxygen through blood to organs and tissues. Exposure can be very dangerous for those with existing heart conditions because they already have impaired oxygen-carrying capacity. At very high levels, exposure to CO can be fatal.

Nitrogen oxides
Long-term exposure to nitrogen oxides increases symptoms of bronchitis in asthmatic children. Research has also shown an increase in emergency room visits and hospital admissions for lung problems, especially asthma, after exposure to short-term increases in NOx. Such exposures are more likely among those spending time on or near major roads.

Sulphur dioxide
This pollutant causes irritation of the eyes, and also inflames the lungs, with coughing and aggravation of asthma and bronchitis. Hospital admissions and mortality from heart disease increase on days of high sulphur dioxide levels. Similarly, higher levels are linked with more admissions for respiratory illness, particularly among children, the elderly, and people with asthma.

Lead
Exposure to lead can affect the nervous system, the kidneys, immunity, the reproductive system, and the heart. Infants and young kids are especially sensitive to even low levels of lead, which may lead to reduced IQ and behavioural problems.

Heavy traffic and areas of industrial activity are the main sources of urban air pollution. Vehicles emit nitrogen oxides, polluting in themselves and also capable of reacting with Volatile Organic Compounds on sunny days to form ground-level ozone. Diesel exhaust is a major source of PM pollution. Therefore, anyone living by or spending time near congested roads is at risk from the health effects of urban pollution. Sulphur dioxide levels may be high in the vicinity of heavy industry and coal-fired power stations.

Well-insulated and poorly ventilated homes, workspaces and schools expose us to a variety of indoor air pollution. Not only does external air pollution accumulate indoors, but structural components, internal fittings in buildings, heating devices, furniture, carpets, paints and cleaning products, can form a toxic indoor atmosphere. Nitrogen dioxide, formaldehyde and sulphur dioxide among others irritate the airways and exaggerate allergic reactions.

Indoor air pollution comes from:

• Building materials Furniture
• Furnishings
• Cooking, Heating
• Smoking 
• Using products like paints, varnishes, cleaning products 
• Outdoor pollution entering through cracks and leaks in a building 
• Natural radon gas entering from the basement of a building – may be less of a concern for those with allergies, but a proven cause of lung cancer.

Indoor pollutants from these sources include nitrogen oxides, carbon monoxide, particulate matter, radon and tobacco smoke, allergens like mould and house dust mite, and Volatile Organic Compounds. While there is plenty of scientific evidence for the health impacts of carbon monoxide and radon, lack of research and monitoring mean that less is known about the dangers of exposure to other indoor pollutants.

The health effects of carbon monoxide, nitrogen oxides and particulate matter pollution are described above. Other health effects of indoor air pollution include:

• Tobacco smoke reduces lung function, triggers asthma attacks and irritates eyes. 
• Allergens trigger rhinitis and asthma. The main allergens in the home are house dust mite droppings, fungal particles, pet dander and pollen. 
• Volatile Organic Compounds irritate the lungs, with children being especially vulnerable. They include both natural and synthetic chemicals like formaldehyde, coming from several sources including construction products, cleaning products, air fresheners, paints and electrical goods.

To find out more visit our Indoor Air Pollution page.

In the UK, there is a nationwide network of air quality monitoring stations. You can check out outdoor air pollution data on the Defra website. We are bound by EU air quality legislation which is mainly focused upon levels of PM and nitrogen oxides pollution.

Here are some handy tips for avoiding exposure to outdoor pollution:

If you are driving behind a diesel vehicle, like a lorry, taxi or bus, keep your car windows closed and keep your distance to protect yourself from the exhaust fumes. Report any vehicle pumping out black smoke to the Vehicle Operator and Services Agency.

There is also a lot you can do to improve your indoor air quality. Here are some suggestions:

A High-Efficiency Particulate Air (HEPA) purifier combined with an activated carbon filter can remove both particulate and gaseous indoor pollution. This might be a particularly wise investment if you happen to live in an urban environment. Vacuum and damp-dust regularly to keep dust levels down. Try to eliminate materials that produce Volatile Organic Compounds like formaldehyde such as chipboard, glues and paints. Keep your home well ventilated and free of damp to get rid of mould spores. Make sure gas appliances are regularly serviced to eliminate nitrogen oxides and carbon monoxide pollution.