ALBERTA AMBIENT AIR QUALITY OBJECTIVES
NITROGEN DIOXIDE
Alberta Ambient Air Quality Objectives
Alberta ambient air quality objectives are issued by Alberta Environment, under Section 14 (1),
the Environmental Protection and Enhancement Act, 1992 (EPEA). Based upon the available
information,

The 1-hour average Alberta Ambient Air Quality Objective for nitrogen dioxide is 300 µg m-3
(159 ppb) based on respiratory effects.

The annual average Alberta Ambient Air Quality Objective for nitrogen dioxide is 45 µg m-3
(24 ppb) based on vegetation.
Characteristics
Nitrogen dioxide (NO2) is a reddish-orange-brown gas with an irritating, acrid, characteristic
pungent odour. At temperatures below 21.15ºC, nitrogen dioxide exists as a brown liquid and at
temperatures below -11ºC, as a colourless solid. Nitrogen dioxide is corrosive, highly oxidizing
and non-combustible.
Nitrogen dioxide occurs naturally in the environment as a result of forest fires, atmospheric
lightning discharges and biogenic oxidation of nitrogen containing compounds present in soil.
Anthropogenic emissions of NO2 are mainly the result of combustion processes, such as the
combustion of fuel for vehicles or the combustion of coal, oil and natural gas for industrial
processes. Nitrogen dioxide can be directly released to air but more often, it is produced by the
conversion of nitric oxide released from combustion processes. In sunlight, nitrogen dioxide can
lead to the formation of ozone, nitric acid and nitrate-containing particles. Emissions of NO2
may also result from its use in industrial processes. Nitrogen dioxide is used as a chemical
intermediate in the production of nitric acid, as a nitrating agent, as an oxidizing agent, as a
catalyst (e.g. in the production of sulphuric acid), as an oxidizer for rocket fuels and as a
polymerization inhibitor for acrylates. It has also been used in the manufacturing of oxidized
cellulose compounds (hemostatic cotton) and in bleaching flour.
The National Pollutant Release Inventory reported that 811,190.7 tonnes of NOx (on a NO2
mass basis) were reported for Alberta in 2006. Ambient levels have declined at most urban
centers between 1990 and 2009. However, concentrations in the Fort McMurray area have
increased since 1999.
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Effects
Human health
Airway inflammation and alterations in lymphocytes (host defense) appear to be sensitive
responses of healthy individuals acutely exposed to NO2 concentrations of 2 ppm or lower.
Whereas, individuals with asthma, chronic obstructive pulmonary disorder (COPD) or chronic
bronchitis have a greater sensitivity to acute NO2 exposures compared to healthy individuals.
Pre-exposure to NO2 can increase the responsiveness of mildly asthmatic individuals to inhaled
allergens (e.g. house dust mite, pollen).
Vegetation
The uptake of the majority of gaseous NO2 is the leaf through the stomatal openings, with a
minority absorbed through the leaf cuticle. A large number of studies have been done on the
effects of NO2 on plants but the effects observed depend on a number of factors, which include
but are not limited to: the sensitivity of the species, duration and concentration of the exposure,
and stage of growth when exposed. Some of the effects that have been observed are: increase
in shoot to root ratio, which results in drought susceptibility; decreased growth; increased shoot
nitrogen, which leads to increased susceptibility to pathogen and insect attack; and advanced
bud-break, which could lead to frost damage.
Other Jurisdictions
The European Union and New Zealand have health based ambient objectives for NO2 with a 1hour average of 200 µg m-3. The US EPA reduced their 1-hour standard to 188 µg m-3 in 2010.
The 1-hour objective of 400 µg m-3 for Canada and Alberta is based on odour. Many
jurisdictions also have annual objectives with limits ranging from 30 µg m-3 (European Union for
vegetation) to 100 µg m-3 (US EPA).
Reference
Alberta Environment. 2007. Assessment Report on Nitrogen Dioxide for Developing Ambient
Air Quality Objectives.