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Terms and Definitions

Air Quality Health Index (AQHI) – Ontario's AQHI is a health protection tool that is designed to help you make decisions to protect your health by limiting short-term exposure to air pollution and adjusting your activity levels during increased levels of air pollution. It is based on three pollutants in our air: ozone, fine particulate matter, and nitrogen dioxide. The AQHI provides a number from 1 to 10+ and a category (Low, Moderate, High, Very High) to indicate the level of health risk associated with local air quality. More information may be found at

Ambient air: Outdoor or open air.

Ambient Air Quality Criteria (AAQC): Maximum desirable average concentrations for specific atmospheric contaminants. AAQC are based upon the effects on the most sensitive endpoint: health, environmental effects, odours, or soiling. Where more than one significant effect occurs, the ministry may have multiple AAQC for the same substance. The averaging time is initially set based on the underlying effect and is sometimes adjusted in order to allow for evaluation of air quality over different averaging periods.

Continuous monitoring – involves collecting and analyzing air quality on a real-time basis. Most continuous monitoring instruments take a measurement once every five minutes, and report an average concentration at the end of each hour.

Detection Limit (DL): The smallest amount of a substance which an instrument can differentiate from 0. This is related to the Method Detection Limit (MDL) which is the lowest amount of a substance that an entire analysis method (media preparation, sampling, extraction, and instrumental analysis) can reliably determine.

Exceedance: A concentration of a parameter that is higher than the AAQC, standard, or other benchmark for that substance.

Micrograms per cubic metre (μg/m3 ): A concentration unit used to report pollutant concentrations in the atmosphere. One microgram is a millionth of a gram.

Micron (μm): One millionth of a metre = one thousandth of a millimetre = about three millionths of a foot. A human hair ranges from 40 to 120 microns thick.

NAPS: Environment and Climate Change Canada’s National Air Pollution Surveillance Program was established in 1969 with the goal of providing accurate and long-term air quality data of a uniform standard across Canada. Through the NAPS program, Environment and Climate Change Canada monitors and assesses the quality of ambient air in the populated regions of Canada. More information may be found at

Nanograms per cubic metre (ng/m3): A concentration unit used to report pollutant concentrations in the atmosphere. One nanogram is a thousandth of a micron.

Non-continuous monitoring – requires collecting an air sample over a 24-hour period (midnight to midnight, EST), which is sent for laboratory analysis.  

Part per billion (ppb): A concentration unit used by various instruments to report gas concentrations in the atmosphere. This is the approximate equivalent of 50 drops of water in an Olympic size swimming pool. Similarly “ppm” means “part per million” a unit which is 1000 times larger.

Glossary of Air Pollutant Abbreviations and Terminology

Nitrogen Dioxide, hourly average, measured in parts per billion.
Ozone, hourly average, measured in parts per billion.
Particulate matter less than 2.5 microns in diameter, 3-hour average, measured in micrograms per metre cubed.
Solar radiation, hourly average, measured in watts per square metre.
Sulphur Dioxide, hourly average, measured in parts per billion TRS Total Reduced Sulphur gases, hourly average, measured in parts per billion. TRS includes hydrogen sulphide (H2S).
Wind Speed, hourly average, measured in kilometers per hour WD Wind Direction that wind blows from, hourly average, measured in degrees (0 to 360 clockwise, 0 and 360 = North, 90 = East, 180 = South, 270 = West).

Working towards improving Sarnia's air quality!