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Sources and Effects

Sources and Effects

traffic soot

Up to a few decades ago, the main source of pollution in urban areas was domestic heating and industry, which used to generate large amounts of particulate matter and sulphur dioxide, resulting from coal burning. Nowadays, the major threat to clean air in urban areas is posed by traffic emissions, but also to a certain extent industry and in particular power generation. Motor vehicles running on petrol or diesel emit a wide variety of pollutants, principally carbon monoxide (CO), oxides of nitrogen (NO_X), volatile organic compounds (VOC) and particulate matter (PM₁₀,PM_2.5) which degrade urban air quality. Some of these so-called primary pollutants eventually react further under the presence of sunlight, which leads to the formation of ozone, a secondary long-range pollutant, which affects rural areas, often far from the original emission site.

The following table lists the main pollutants, their sources and relative effects on human health: Pollutant
Principal Source
Effects on Human Health
Sulphur Dioxide (SO₂)
Power stations burning fossil fuels and motor vehicles running on diesel (with high sulphur content).
Decreased lung function.
Particulate Matter (PM_2.5, PM₁₀, TSP or SPM)
Road traffic emissions (particularly from diesel vehicles) and power generation.
They are carried deep into the lungs and cause inflammation and exacerbate heart and lung disease. They may carry surface-absorbed carcinogenic compounds into the lungs.
Carbon Monoxide (CO)
Combustion processes.
This gas prevents the normal transport of oxygen by the blood.
Nitrogen Dioxide (NO₂) and Nitrogen Oxide (NO) - collectively known as Oxides of Nitrogen (NO_X)
Road traffic, power stations, heating plants and industrial processes.
Nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections such as influenza.
Ozone (O₃)
Secondary pollutant produced by reaction between nitrogen dioxide (NO₂), hydrocarbons and sunlight.
Irritates the airways of the lungs, exacerbating symptoms of those suffering from asthma and lung disease.
Volatile Organic Compounds (VOC)
VOC are released in vehicle exhaust gases either as unburned fuels or as combustion products; evaporation of solvents and motor fuels.
Chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Benzene (a VOC)
Distribution and combustion of petrol.
Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
1,3-Butadiene (a VOC)
Emitted into the atmosphere principally from fuel combustion of petrol and diesel vehicles; an important chemical in the manufacture of synthetic rubber.
Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Toxic Organic Micropollutants (TOMP) e.g. PolyAromatic Hydrocarbons (PAH), PolyChlorinated Biphenyls (PCB), Dioxins and Furans
Incomplete combustion of fuels
TOMP can causing a wide range of effects, from cancer to reduced immunity to nervous system disorders, and interfere with child development.
Lead and other (heavy) metallic compounds
Fossil fuel combustion (including vehicles), metal processing industries and waste incineration
Harmful, especially to infants and young children. In addition, lead absorbed by pregnant women can interfere with the health of the unborn child. Exposure has also been linked to impaired mental function, impaired visual-motor performance and neurological damage in children, and memory and attention span deficiency.

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Pollutant	Principal Source	Effects on Human Health
Sulphur Dioxide (SO₂)	Power stations burning fossil fuels and motor vehicles running on diesel (with high sulphur content).	Decreased lung function.
Particulate Matter (PM_2.5, PM₁₀, TSP or SPM)	Road traffic emissions (particularly from diesel vehicles) and power generation.	They are carried deep into the lungs and cause inflammation and exacerbate heart and lung disease. They may carry surface-absorbed carcinogenic compounds into the lungs.
Carbon Monoxide (CO)	Combustion processes.	This gas prevents the normal transport of oxygen by the blood.
Nitrogen Dioxide (NO₂) and Nitrogen Oxide (NO) - collectively known as Oxides of Nitrogen (NO_X)	Road traffic, power stations, heating plants and industrial processes.	Nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections such as influenza.
Ozone (O₃)	Secondary pollutant produced by reaction between nitrogen dioxide (NO₂), hydrocarbons and sunlight.	Irritates the airways of the lungs, exacerbating symptoms of those suffering from asthma and lung disease.
Volatile Organic Compounds (VOC)	VOC are released in vehicle exhaust gases either as unburned fuels or as combustion products; evaporation of solvents and motor fuels.	Chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Benzene (a VOC)	Distribution and combustion of petrol.	Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
1,3-Butadiene (a VOC)	Emitted into the atmosphere principally from fuel combustion of petrol and diesel vehicles; an important chemical in the manufacture of synthetic rubber.	Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Toxic Organic Micropollutants (TOMP) e.g. PolyAromatic Hydrocarbons (PAH), PolyChlorinated Biphenyls (PCB), Dioxins and Furans	Incomplete combustion of fuels	TOMP can causing a wide range of effects, from cancer to reduced immunity to nervous system disorders, and interfere with child development.
Lead and other (heavy) metallic compounds	Fossil fuel combustion (including vehicles), metal processing industries and waste incineration	Harmful, especially to infants and young children. In addition, lead absorbed by pregnant women can interfere with the health of the unborn child. Exposure has also been linked to impaired mental function, impaired visual-motor performance and neurological damage in children, and memory and attention span deficiency.