Working in partnership for the people of Herefordshire
The pollutants assessed and reviewed by the Council
There are eight pollutants that are of concern in the National Air Quality Strategy which were selected because of their potential health effects.They are:
- Benzene
- 1,3-butadiene
- Carbon monoxide
- Lead
- Nitrogen dioxide
- Particulates (PM10)
- Sulphur dioxide
- Ozone
Benzene
Sources
Volatile Organic Compounds (VOCs) can be released in vehicle exhaust gases either as unburned fuels or as combustion products. They can also be emitted by the evaporation of solvents and motor fuels.
Benzene is a VOC which is a minor constituent of petrol. The main sources of benzene in the atmosphere in the UK are the distribution and combustion of petrol. Of these, combustion by petrol vehicles is the single biggest source, being up to 70%.
Effects
Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
1,3-butadiene
Sources
Like benzene, this pollutant is another organic chemical associated with traffic. It is not present in vehicle fuel, but is formed by chemical reactions when fuels are burnt and emitted in the exhaust. It is also used industrially, mainly in the production of synthetic rubber for tyres. At the few locations where it is handled in bulk, industrial sources may be significant, but generally traffic is the only significant source.
Effects
Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Carbon Monoxide
Sources
Carbon monoxide (CO) is a toxic gas which is emitted into the atmosphere as a result of combustion processes, and is also formed by the oxidation of hydrocarbons and other organic compounds. In the UK’s urban areas, CO is produced almost entirely (90%) from road traffic emissions. It survives in the atmosphere for a period of approximately one month, but is eventually oxidised to carbon dioxide (CO2).
Effects
This gas prevents the normal transport of oxygen by the blood. This can lead to a significant reduction in the supply of oxygen to the heart, particularly in people suffering from heart disease.
Lead
Sources
Lead is widely used for manufacturing products. The largest use is within batteries, but it is also used as an alloy (solders, gunmetal), in pigments, as well as in its pure state as a metal.
Lead has historically been used as a compound (tetraethyl lead) in petrol to improve its performance. The use of lead in petrol has declined fast since the early 1990s. However, some airborne emissions still come from older petrol cars unable to use unleaded.
The second most significant source of lead is from the non-ferrous metals industry, where foundries can lead to significant local emissions.
Effects
Lead in air may affect people either by being absorbed through the lungs or through the digestive tract when it settles out, contaminating soil, dusts, water, and hence food. Lead, taken into the body, causes biotoxic effects in a range of body systems. At the low levels to which the public are exposed, the effects of concern are on the growth of blood cells, on the nervous system, and on blood pressure. Because of the fact that they are growing, children are likely to be more susceptible than adults are. And there is concern that chronic exposure to levels of lead lower than those necessary to produce symptoms of lead poisoning can have subtle effects on neurophysiological function, and perhaps may prevent children achieving their full mental and physical potential.
Nitrogen dioxide
Sources
Nitrogen Dioxide is an acid gas produced by any combustion in air. The largest source is road transport (46%) followed by the power generation industry (22%), industry and commerce (12%) and domestic heating (3%).
Effects
Nitrogen Dioxide is known to reduce the efficiency of breathing and to increase the irritability of airways in the lungs. These effects are reversible. There is evidence that it increases allergic reactions in the lung, reduces resistance to infection, and that exposure of children can lead to poorer lung function in later life.
Particulates (PM10)
Sources
Particles in the air come from a range of sources and vary widely in size and chemical composition from place to place and time to time. Natural sources include pollen and sea spray; industrial sources include combustion processes, quarrying and aggregate handling; and transport sources include diesel vehicle exhaust emission, and dust from tyre and brake wear. Other sources, such as smoking, produce by far the greatest concentration of particles ingested by those who smoke.
Secondary particulates also occur where other pollutants in the atmosphere combine to form small solid particles.
It is difficult to estimate the relative contribution to the particles in the air for any one place, but in 1995, transport was the biggest source of primary particles, accounting for some 25%, power generation emitting 15%, mining and quarrying emitting 12%, and domestic and commercial heating, 11%.
Effects
The effects are likely to vary depending on what the particles in the air actually are, and because it is difficult to do studies on large populations, which can distinguish between different mixtures, the findings tend to be rather generalised. It is now accepted widely that populations living in areas with higher airborne particle concentrations show a range of differences in health to otherwise similar people. The effects include higher death rates, respiratory and circulatory effects and cancer.
Sulphur dioxide
Sources
Sulphur dioxide is an acidic gas which combines with water vapour in the atmosphere to produce acid rain. Both wet and dry deposition have been implicated in the damage and destruction of vegetation and in the degradation of soils, building materials and watercourses. SO2 in ambient air can also affect human health, particularly in those suffering from asthma and chronic lung diseases.
The principal source of this gas is power stations burning fossil fuels, which contain sulphur. Major SO2 problems now only tend to occur in cities in which coal is still widely used for domestic heating, in industry and in power stations. As many power stations are now located away from urban areas, SO2 emissions may affect air quality in both rural and urban areas. The last 40 years have seen a decline in coal burning (domestic, industrial and in power generation) As a result, ambient concentrations of this pollutant in the UK have decreased steadily over this period.
Both the Air Quality Strategy and the EU 1st Daughter Directive (1999/30/EEC) contain limit values for ambient concentrations of sulphur dioxide.
Effects
Even moderate concentrations may result in a fall in lung function in asthmatics. Tightness in the chest and coughing occur at high levels, and lung function of asthmatics may be impaired to the extent that medical help is required. Sulphur dioxide pollution is considered more harmful when particulate and other pollution concentrations are high.
Ozone
Sources
Ozone is a secondary pollutant. It is not emitted directly, but is formed in the atmosphere from the combination under the influence of sunlight of oxides of nitrogen (NOx comes from combustion sources) and volatile hydrocarbons (mainly emitted from transport and industry). Ozone levels are generally higher usually in rural areas, downwind of the sources (which are usually urban areas) of the primary pollutants which precede it.
The original sources of NO2 and VOC can be hundreds or even thousands of miles away, which is why the National Air Quality Strategy does not impose any obligations on Herefordshire Council to reduce this pollutant – the sources are outside of the county and therefore beyond the Council’s jurisdiction.
Effects
Ozone can make the airways of the lungs inflamed and more responsive to factors causing them to constrict, thus reducing breathing efficiency. There is no evidence of particular long-term effects at this time.