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Public Health Ontario releases review of air quality indices

“Review of Air Quality Index and Air Quality Health Index” is the most comprehensive review to date in Canada

Toronto, January 30, 2013Public Health Ontario has conducted the most comprehensive review to date of air quality indices in Canada. Using data from Ontario, the Review of Air Quality Index and Air Quality Health Index report examines the strengths and limitations of these two indices of air and presents evidence to inform future directions regarding their use.

“It is our hope that readers will have a better understanding of air pollution and the two indices that are in use in Ontario to summarize air pollution in the short-term,” said Dr. Ray Copes, Chief of Environmental and Occupational Health, Public Health Ontario, and one of the authors of the report. “It’s important to recognize that both of these indices are real-time indices and give us a very short-term snapshot of air pollution conditions.”

Many jurisdictions have developed numerical indices of air quality, and the Air Quality Index (AQI) and the Air Quality Health Index (AQHI) are being used as indicators of ambient levels of air pollution in Canada. These indices characterize ambient levels of air pollution present at a given time, and they serve as the basis for communicating the health significance of air pollution to the public. Although the two indices have been used concurrently over five years, to date no one has undertaken a comprehensive review of the comparability of the indices. This review provides useful input to policy-makers in making decisions on the tools or indices they’d like to use for summarizing short-term air pollution.
Some notable findings from the report:
Variation in day-to-day values. The AQI showed more variation in day-to-day values as it uses a 100-point scale for measurement. The AQHI uses a 10-point scale.

Differences in calculation. The AQHI is always calculated using three key air pollutants; the AQI is potentially influenced by a larger number of air pollutants, but the level at any point in time is based solely on one pollutant.

Difference in number of days in high-risk range. Under certain conditions, the AQHI tended to trigger more days in the high-risk range or advisories in 20032006. In more recent years (20072010), this is no longer the case.

Differences in worst pollution days. While the AQI identified high-risk days mostly in the warm season, the AQHI selected some cold days as being high pollution days.
Strong correlation between indices in summer. Correlation of the two indices using recent Ontario air pollution data showed better and consistent correlation in the summer versus the winter. The correlation was strongest at some of the rural monitoring stations.

A recent improvement in air pollution. Trend analysis illustrated an improvement in air pollution in 200810 versus data from 200306.

An important limitation of both indices is they do not recognize health effects associated with long-term exposure to air pollution. Further, they do not recognize the importance of location within a community related to an increased risk of exposure to ambient air pollution. “The science that has been done on air pollution and health over the last couple of decades has made it clear that long-term exposure to air pollution is even more hazardous than short-term exposure. That’s not well captured by either of these two indices,” said Copes. “Long-term exposure to air pollution is an issue that impacts everyone, not just the frail and elderly,” said Dr. Hong Chen of Public Health Ontario, a co-author of the report. “Long-term exposure can lead to a host of chronic diseases.”

This report is a first step at looking at the broader issue of the health effects of air. “It’s essential that everyone, including federal and provincial entities, and local health units, keep tabs on air pollution, look at what those risks are, and how much illness and premature death we encounter due to those pollutants,” said Copes. “While the data from our report shows air pollution has decreased, the problem is far from eliminated and more action is required if we want to further reduce the burden on human health.”

The report is available on Public Health Ontario’s website at:

Public Health Ontario is a Crown corporation dedicated to protecting and promoting the health of all Ontarians and reducing inequities in health. Public Health Ontario links public health practitioners, front-line health workers and researchers to the best scientific intelligence and knowledge from around the world.

For more information, please contact:
Nicole Helsberg
Public Health Ontario
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Page last updated: 2016-07-07 11:24 AM
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