International comparison of urban air quality indicators: data sources and methods, chapter 2

2. Description and rationale of the International Comparisons of Urban Air Quality indicators

2.1 Description

The International Comparison of Urban Air Quality indicators compare ambient levels (concentrations) of air pollutants in selected Canadian urban areas with levels in selected international urban areas. The indicators report the concentration of ground-level ozone (as the annual average of the daily maximum 8-hour average), fine particulate matter, sulphur dioxide and nitrogen dioxide (as the annual average of the daily 24-hour average) in ambient air.

2.2 Rationale

Fine particulate matter and ozone are key components of smog and two of the most widespread air pollutants to which people are exposed. Nitrogen dioxide and volatile organic compounds react in the presence of sunlight to produce ozone. Nitrogen dioxide and sulphur dioxide contribute to acid deposition and to the formation of fine particulate matter. Exposure to air pollution, even at low concentrations, has been linked to a number of adverse effects on health.

The air quality indicators are state/condition indicators intended to provide information about the progress made toward improving ambient air quality. These indicators are also intended to provide a general comparison of ambient levels of air pollutants in selected Canadian urban areas with those measured in other international urban areas.

2.3 Recent changes to the indicators

The geographical coverage of the indicators has changed for this edition as data for South Africa (more specifically, Pretoria's metropolitan area) was not available at the time of production.