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Palliser Airshed Society

Ground Level Ozone (O3)

Ozone is a very reactive, colourless gas made up of three atoms of oxygen. Ozone is considered a secondary pollutant as it is created through reactions with other airborne substances. It can react with other pollutants to form photochemical smog.

Ground level ozone refers only to the formation of ‘bad ozone’ near the earth’s surface (Troposphere). A layer of ozone here results in the formation of fog. The ‘Ozone Layer’, or ‘Good Ozone’ is found in the Stratosphere where it acts to protect the earth’s surface from the harmful effect of ultra-violet (UV) rays from the sun.

How Is It Generated?

The largest source of ozone is vehicle exhaust. Other anthropogenic sources include: industry and chemical solvents. Natural sources include: lightning and some vegetation species.

What Are The Health Effects?

Provincial Guidelines:

What Can We Do?

  1. Reduce the amount of vehicle use.
  2. Use alternative transportation (car pool, walk, bike, use public transportation)
  3. Use Alternative fuels (wind & solar).
  4. Conserve energy. Use ‘muscle power’ rather than fuel powered machines (eg: use rake rather than lawn blower).

Table of Human Symptoms and Other Effects

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


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