Respiratory Diseases in Children

4. Can outdoor air pollution contribute to respiratory diseases in children?

• 4.1 Which pollutants are present in outdoor air?
• 4.2 What respiratory diseases can outdoor pollution lead to?
• 4.3 Does exposure to pollen lead to respiratory allergies?

There is clear evidence that air pollution is associated with troublesome respiratory symptoms in children. However, it is less clear whether specific pollutants are directly responsible for the development of respiratory diseases. More...

4.1 Which pollutants are present in outdoor air?

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See also GreenFacts' Digest on Air Pollution

Particulate matter is the sum of all solid and liquid particles suspended in air. Many of these particles are due to the burning of fuel for energy and transport. In Europe, overall concentrations of particulate matter (PM₁₀) in outdoor air have generally decreased between 1996 and 2000. However, near busy roads, concentrations often exceed recommended limits, because of motor vehicle emissions.

Another type of pollution are gases, such as ozone (O₃), sulphur dioxide (SO₂), and nitrogen oxides (NO_x)

• Ground level Ozone (O₃) is a pollutant that is formed under the action of light from other air pollutants, particularly during sunny weather. In the last few years annual average concentrations have generally increased, whereas short term peak concentrations have remained stable.
• Nitrogen dioxides (NO₂) that results from fuel combustion is a major contributor to smog and acid rain. Concentrations have generally decreased between 1996 to 2000, but in some traffic hot-spots and urban centres recommended values are exceeded.
• Sulphur dioxide (SO₂) is a gas released mainly by industrial processes, most notably by coal power plants. It is a major contributor to acid rain. Urban and local SO₂ concentrations continue to decrease in most areas in Western Europe, but short-term peaks still represent a problem in some industrial hot-spots.

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4.2 What respiratory diseases can outdoor pollution lead to?

There is increasing evidence that the most common air pollutants (PM, O₃, NO_x and SO₂) adversely affect the respiratory health of children. While air pollution may not be the main cause of the greater frequency of respiratory disease, it significantly worsens the symptoms. When levels of air pollution are high, an increase in the number of hospital admissions and emergency room visits is observed.

Particular attention is currently given to particles in air which can be breathed in and that are small enough to enter deep into the lung, as these may be a major contributor to the adverse effects of air pollution.

Some studies suggest that living near busy roads is linked to respiratory problems including reduced lung function, as well as to a higher prevalence of asthma and respiratory symptoms such as wheezing.

Studies that compare two groups of people exposed to different levels of air pollution provide the strongest evidence for a relationship between respiratory disease and air pollution.

For example, the temporary closing of a steel mill in the Utah Valley in the late 1980’s provided researchers with the unique opportunity to demonstrate a relationship between exposure to air pollution particles and respiratory health. During the mill’s closure the number of children with respiratory symptoms admitted into hospital decreased substantially and then increased to pre-strike levels when the mill reopened. Another study followed 110 children who were relocated to areas with either more or less air pollution. Those who moved to less polluted areas showed an increase in lung function, and those who moved to more polluted areas showed a decrease. More...

4.3 Does exposure to pollen lead to respiratory allergies?

Pollen allergies are caused by some specific substances released from pollen into the air (pollen allergens). In Europe pollen allergens may be responsible for 10-20% of allergic diseases. Although the relationship between pollen allergens and hayfever (allergic rhinitis) is clear the relationship between pollen allergens and asthma is less clear.

In different regions different plant species are responsible for pollen allergies. For instance, grasses and birch trees are the main cause of pollen allergies in Northern and Central Europe, ragweed in Central and Eastern Europe, and olive trees and cypresses in Southern Europe.

The occurrence of allergic reactions depends on the length of the pollen season, the amount of pollen in the air, the number and level of the pollen peaks, and how readily allergens are taken up by the body.

One study has suggested that in highly polluted areas air pollution may increase the frequency of pollen allergies. However, other studies have not shown such a relationship and another recent study carried out on children during the pollen season suggested that air pollution does not increase pollen-related allergies.

Global climate change might cause particular plant species to spread to new areas which become climatically suitable. Warming may cause an earlier and longer pollen season for some species. It remains uncertain how these changes would affect the frequency and severity of allergies in different regions. More...