Ground Level Ozone


Ozone (O3) is both a natural component of the atmosphere and a major constituent of photochemical smog. At normal atmospheric concentrations it is an odourless, colorless gas. However, at concentrations higher than one ppm, such as found near photocopier machines and near electrical discharges, it has a sharp odour.

Ozone is a strong oxidizer and can irritate eyes, nose and throat and decrease athletic performance. High concentrations can increase susceptibility to respiratory disease and reduce crop yields.


Unlike other pollutants, ozone is not emitted directly into the atmosphere but is produced through a series of chemical reactions in the atmosphere. Concentrations are controlled mainly by emissions of nitrogen oxides and reactive hydrocarbons. Ozone is a natural component of the upper atmosphere and may be transported to ground level by meteorological processes.

Alberta Guidelines

Alberta Environment and Parks guidelines for ozone are:

  • a 1-hour average of 82 ppb
  • a 24-hour average of 25 ppb
Concentration (ppb) Exposure Time Human Symptoms and Other Effects
10,000 Severe pulmonary edema; possible acute bronchiolitis; decreased blood pressure; rapid weak pulse
1,000 Coughing; extreme fatigue; lack of coordination; increased airway resistance; decreased forced expiratory volume
500 Chest constriction; impaired carbon monoxide diffusions capacity; decrease in lung function without exercise
300 Headache; chest discomfort sufficient to prevent completion of exercise; decrease in lung function in exercising subjects
250 Increase in incidence and severity of asthma attacks; moderate eye irritation
150 For sensitive individuals, reduction in pulmonary lung function; chest discomfort; irritation of the respiratory tract, coughing and wheezing
150 Threshold for injury to vegetation
120 US national primary and secondary ambient air quality standard
100 Maximum allowed by OSHA in industrial work areas
82 1 hour Alberta ambient air quality guideline
50 Maximum recommended by ASHRAE in an air conditioned and ventilated space
20–40 Range in which ozone occurs in healthy outdoor environments. Also ozone level produced by some indoor air ionizers when operated according to instructions.
25 24 hour Alberta ambient air quality guideline
3–10 Low range at which average person can smell ozone
1 Most indoor environments — windows open

Air Quality Data

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Ground Level Ozone (O3) Trends

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