Oxides of Nitrogen


Oxides of nitrogen (NOx), mostly in the form of nitrogen oxide (NO) and nitrogen dioxide (NO2), are produced by the high temperature combustion of fossil fuels. Nitrogen oxide is the predominant species emitted by combustion sources but it is rapidly changed to nitrogen dioxide in the atmosphere.

Nitrogen dioxide is a reddish-brown gas with a pungent irritating odour. It has been linked to respiratory disease and contributes to acid rain. It plays a major role in atmospheric photochemical reactions and ground level ozone formation and destruction.

Exposure of vegetation to high concentrations of nitrogen oxides results in silvering of the lower leaf surface. A waxy appearance appears shortly after exposure followed by bronzing after two or three days.


The primary emitting sources are transportation sources (e.g. on-road and off-road motor vehicles and engines, rail), fossil-fuelled electric power plants as well as upstream oil and gas industry (e.g. natural gas plants, oil sands).

Alberta Guidelines

Alberta Environment and Parks guideline are based on the prevention of human health effects. They are equal to the most rigorous of Environment Canada's ambient air quality objectives.

The Alberta Guidelines for nitrogen dioxide, the major component of nitrogen oxides in the ambient atmosphere are:

  • 1-hour average of 210 ppb
  • 24-hour average of 110 ppb
  • an annual average of 30 ppb
Concentration (ppb) Exposure Time Human Symptoms and Other Effects
300,000 Rapid death
150,000 Death after 2 or 3 weeks by bronchiolitis fibrosa obliterans
50,000 Reversible, nonfatal bronchiolitis
10,000 Impairment of ability to detect odour of NO2
5,000 15 min Impairment of normal transport of gases between the blood and lungs in health adults
2,500 2 hours Increased airway resistance in healthy adults
2,000 4 hours foliar injury to vegetation
1,000 15 min Increased airway resistance in adults with bronchitis
1,000 48 hours Slight leaf spotting of pinto bean, endive, and cotton
300 Brownish color of target — 1 km distant
250 Decrease of growth and yeild of tomatoes and oranges
210 1 hour Alberta ambient air quality guideline
200 8 hours Yellowing of white fabrics
120 Odour perception threshold
110 24 hours Alberta ambient air quality guideline
100 12 weeks Fading of dyes on cotton and rayon
100 20 weeks Reduction of growth of Kentucky bluegrass
30 annual Alberta ambient air quality guideline
30 Brownish color of target — 10 km distant
3 Brownish color of target — 100 km distant

Air Quality Data

Date Range – From
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Oxides of Nitrogen (NOX) Trends

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