The Science of Air Quality

Air Quality is the result of complex interactions that involve the chemistry and meteorology of the atmosphere, as well as the emissions of a variety of pollutants from sources that are both natural and anthropogenic. The pollutants associated with air quality and measured by the new AQHI are ground-level Ozone (O3 or GLO), fine and course Particulate Matter (PM2.5/PM10) and Nitrogen Oxides (NOx). 

The AQHI is calculated based on the relative risks of common air pollutants that are known to harm human health.

smogGround-level ozone (GLO) is not emitted into the air directly.  It is a “secondary” pollutant formed from a set of photochemical reactions, or reactions that occur under the presence of sunlight.  High levels of GLO typically occur from May-September in Canada and from morning to early evening.  Ozone precursors are nitrogen oxides and volatile organic compounds which react with sunlight to form GLOGLO irritates the respiratory tract and eyes. Exposure to high levels of GLO results in chest tightness, coughing and wheezing. People with respiratory and heart problems and children are at a higher risk. Ozone has been linked to increased hospital admissions and premature death. 

Particulate matter can either be directly emitted into the air “primary” or formed in the atmosphere via chemical reactions “secondary.” Examples of particulate matter include (soot from forest fires, particles from smokestacks and electrical power plants, sea salt, and dust, just to name just a few. Exposure to particulate matter has been associated with hospital admissions and several serious health effects, including premature death.

rush hourNitrogen oxides include nitrogen oxide (NO) and nitrogen dioxide (NO2).  The primary sources of nitrogen oxides are motor vehicles, power plants, and waste disposal systems.  High concentrations are believed to contribute to heart and lung problems.  Nitrogen oxides are highly reactive gases that play a key role in producing ground-level ozone. 

Other measured pollutants such as Sulfur Dioxide SO2 and Carbon Monoxide (CO) are also air pollutants but were not included in the AQHI. This is because they were not associated with additional health risks in a multi pollutant model consisting of the aforementioned three pollutants.