Pollutants

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. Both the Air Quality Strategy and the EU 1st Daughter Directive (1999/30/EEC) contain limit values for ambient concentrations of sulphur dioxide.

Particulate matter (PM10)
Airborne particulate matter varies widely in its physical and chemical composition, source and particle size. PM10 particles (the fraction of particulates in air of very small size (<10 µm)) are of major current concern, as they are small enough to penetrate deep into the lungs and so potentially pose significant health risks. Larger particles meanwhile, are not readily inhaled, and are removed relatively efficiently from the air by sedimentation. The principal source of airborne PM10 matter in European cities is road traffic emissions, particularly from diesel vehicles.

Carbon Monoxide (CO)
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 European 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).

Nitrogen Dioxide (NO2)
Nitrogen oxides are formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel. The principal source of nitrogen oxides - nitric oxide (NO) and nitrogen dioxide (NO2), collectively known as NOx - is road traffic, which is responsible for approximately half the emissions in Europe. NO and NO2 concentrations are therefore greatest in urban areas where traffic is heaviest. Other important sources are power stations, heating plants and industrial processes.

Ozone (O3 )
Ground-level ozone (O3 ), unlike other pollutants mentioned , is not emitted directly into the atmosphere, but is a secondary pollutant produced by reaction between nitrogen dioxide (NO2 ), hydrocarbons and sunlight. Ozone levels are not as high in urban areas (where high levels of NO are emitted from vehicles) as in rural areas. Sunlight provides the energy to initiate ozone formation; consequently, high levels of ozone are generally observed during hot, still sunny, summertime weather.

Health Effects
Ozone irritates the airways of the lungs, increasing the symptoms of those suffering from asthma and lung diseases.

Volatile Organic Compounds (VOCs)

VOCs are released in vehicle exhaust gases either as unburned fuels or as combustion products, and are also 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 Europe are the distribution and combustion of petrol. Of these, combustion by petrol vehicles is the single biggest source (70% of total emissions).

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

Health Effects
Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects