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Pollution Band (Index)

Health Impact

Low (1-3)

Effects are unlikely to be noticed, even by people who know they are sensitive to air pollution.

Moderate (4-6)

Mild effects are unlikely to require action, but may be noticed by sensitive people.

High (7-9)

Sensitive people may notice significant effects, and may have to take action to reduce or avoid them (for example, by reducing time spent outdoors). Asthmatics will find that their 'reliever' inhaler is likely to reverse the effects of pollution on their lungs.

Very High (10)

The effects on sensitive people, described for 'high' levels of pollution, may worsen.

Sources

Nitrogen dioxide is a colourless and odourless gas produced mainly via combustion, sources include vehicle exhausts, gas appliances, industrial heating and heat treatment and power stations. Emissions arise in the form of NOx, a mixture of nitric oxide (NO) and nitrogen dioxide (NO2). NO2 is also formed in the atmosphere as a result of chemical reactions, influenced by sunlight. Nitrogen dioxide levels also influence the increase in ground level ozone formation.

Health effects

Healthy people will not be troubled by nitrogen dioxide, even during times where levels are high. For persons with breathing difficulties exposure to NO2 can affect lung function and lead to the airway being more sensitive. Asthmatics are at a small risk of being affected if they exercise during times of high pollution levels. However, some research has found no change in lung function even at high concentrations. It is extremely unlikely that outdoor concentrations normally experienced in South Yorkshire will reach such high concentrations (575 micrograms of nitrogen dioxide per cubic meter of air). Some reports also state that asthmatics could be more sensitive to irritant chemicals and allergens, such as house dust mite and pollen, after being exposed to NO2.

Sources

Sulphur Dioxide (SO2) is produced when a material, or fuel, containing sulphur is burned. Globally, much of the sulphur dioxide in the atmosphere comes from natural sources, but in the UK the major contributors are power stations (65% of the total emissions). Sulphur dioxide pollution episodes only generally occur where there is widespread domestic use of coal or in the vicinity of coal-fired or oil-fired power stations.

Health effects

Exposure to the highest concentrations in outdoor air is unlikely to have an effect on the well-being of healthy persons. However those suffering from asthma or other breathing problems are much more sensitive to SO2. Effects on peoples breathing, particularly in these sensitive groups, happens soon after exposure to the pollutant. Short-term exposure to high levels of sulphur dioxide may cause coughing, tightening of the chest and irritation of the lungs.

Sources

Particulate matter air pollution consists of a mixture of particles suspended in the air we breathe. PM10 are particles less than 10 microns in size (a micron is one 1000th millimetre. Compare this with the diameter of an average hair at around 75 -100 microns in diameter). PM10 particles are produced naturally by volcanoes, wind-blown fine sand and soil, sea salt and mould spores, or can result from human activity e.g. emissions from transport and power stations. PM10 particles are also formed in the atmosphere from other pollutants e.g. sulphates and nitrates. Because these particles are so small, some can stay airborne for several days and travel from as far a field as Eastern Europe, and the Sahara. However, in general the highest levels are found next to busy roads.

Health effects

The particles of most interest are those small enough to be breathed into the deepest part of the lung and are known as PM10. Particles larger than this are filtered out in our upper respiratory tract. Particulates are amongst the most harmful of air pollutants to human health. This is especially the case for people with pre-existing lung and heart problems for whom exposure may trigger asthma attacks or cause hospitalisation in severe cases. For the most vulnerable in the UK, exposure to particle pollution may be causing 10,000 early deaths per year. Future research is likely to concentrate on understanding how particulates cause ill health and look at particle numbers and size in relation to health effects. There is still considerable debate as to whether it is the number of particles or mass that is significant to health, however, it is known that these particles are inhaled deep into the lungs, where, over time, they will reduce lung capacity and function.

Sources

Carbon monoxide (CO) is a colourless, odourless poisonous gas produced by incomplete, or inefficient, combustion of fuel including 'cold' or badly tuned engines. It is estimated that road transport is responsible for almost 90% of all Carbon Monoxide emissions in the UK. Badly ventilated domestic fuel appliances (gas, oil or solid fuel) can cause high levels indoors, as can smoking. As traffic is a major source of carbon monoxide, ambient concentrations will generally be highest close to busy roads. Monitoring data suggests that annual average CO levels have gone down dramatically over the last few years.

Health effects

CO gas reduces the transport of oxygen around the body by the blood. This happens when CO interferes with the transport of oxygen by red-blood cells and by blocking essential biochemical reactions. At typical environmental concentrations the effects in healthy persons are of little consequence. However, to persons with angina and disease of the coronary arteries, the effects may be more serious. The Government objective of 10 milligrams of CO per cubic metre of air by 2003 was set to protect those people with increased susceptibility to this gas. This objective has been met at all locations across the UK.

Sources

Ground Level* Ozone (O3) is harmful to health. Ozone is not directly emitted, but is formed by a complex set of reactions involving NOx and volatile organic compounds, usually some distance away from the source. Due to these reactions, ozone levels are actually lower next to busy roads, yet higher in rural locations than in cities. Once formed, ozone can remain in the atmosphere for many days and is often transported over long distances. (*As opposed to stratospheric ozone present in the “ozone layer” which is beneficial as it prevents dangerous radiation from the sun damaging life on Earth)

Health effects

Ozone can irritate the respiratory system. This might come in the form of coughing or an uncomfortable feeling in the chest. Symptoms may last a few hours after exposure. Ozone can aggravate asthma. High ozone levels result in a greater number of asthma attacks; this is because asthmatics are more affected by the irritant. Ozone also makes people more sensitive to allergens that cause asthma attacks. There is a concern that the developing lungs of children repeatedly exposed to high levels of ozone may be damaged. Some studies in animals suggest that ozone may also harm the ability to fight off respiratory infections.

Sources

Hydrocarbons (including benzene) are strongly linked to traffic pollution and are a group of volatile organic compounds (VOCs). Certain VOCs are known to cause cancer; current attention is focused on 1,3 butadiene (primarily from vehicle exhausts), and benzene. Benzene in the atmosphere either comes from the combustion or evaporation of petrol. Levels are therefore highest close to busy roads or in the vicinity of petrol filling stations. The Governments objectives for benzene and 1,3-butadiene have both been met in 2003 for the whole country. A new objective has been set for benzene which must be achieved in 2010.

Health effects

Long-term exposure to high levels of benzene and 1,3 Butadiene has been linked to leukaemia and cancer.