Children breathe more rapidly and take in relatively more air per breath compared to adults, and because they spend more time outdoors than do adults, they tend to be more exposed to outdoor air pollution.

Exposures of Concern

Outdoor Air

Outdoor pollutants represent an equivalent risk to children’s respiratory health. Because children breathe more rapidly and take in relatively more air per breath compared to adults, and because they spend more time outdoors in the summer being physically active than do adults, they tend to be more exposed to outdoor air pollution.

From Wallace and Cooper, 1986. Reproduced with permission.

There are several kinds of air pollutants that can affect children’s respiratory health. The most important of these are the so-called "criteria pollutants," the components of smog, namely, ozone and particulates. Also in this group are nitrogen oxides, sulphur dioxide and carbon monoxide.

Criteria air pollutants:

• Particulates
• Ground-level ozone
• Sulfur dioxide
• Oxides of nitrogen (NO_x)

Particulates refers to fine solid particles that also result from the burning of fossil fuels and emissions from industrial operations. These particles are of extremely small diameter, either less than 10 microns (PM₁₀) or less than 2.5 microns (PM_2.5), and therefore they remain suspended in air.

Ground level ozone is the result of the interaction in the atmosphere in the presence of oxygen and sunlight of several precursor air pollutants, such as oxides of nitrogen (NO_x) and volatile organic compounds (VOCs).

Acid aerosols are fine suspended liquid particles that are mostly sulphates derived from burning fossil fuels. (See the descriptions for SO₂ and NO₂ in indoor air.)

Air toxics are chemicals that are measured at significantly lower levels in outdoor air than the criteria pollutants, and include chemicals such as:

• VOCs
• Pesticides
• Heavy metals
• PAHs (Polycyclic Aromatic Hydrocarbons)
• Benzene

Respiratory Effects

Exposure of children to smog air pollutants is associated with a number of different symptoms including:

• decreased lung function
• increased respiratory symptoms (such as sore throat, cough)
• aggravation of asthmatic symptoms17

High levels of smog have also been associated with increases in:

• hospital emergency visits
• hospital admissions
• absences from school18,19,20

Both ozone and particulates have been shown to have no threshold of effect, in relation to increasing hospital admissions. This demonstrates that they cause health effects even at low levels and are responsible for tangible increases in the burden of illness on health care.

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