Air Quality Index (AQI)
The pollutants
Ozone (O3)
Characteristics and Description
Ozone is a gas comprised of three oxygen
(O3)
atoms. It is unstable and reacts easily to other gases. In its natural
state, it is a component in several levels of the atmosphere. At high
altitudes, it provides protection by absorbing large amounts of
ultraviolet radiation. At ground level, however, high concentrations pose
a health and environmental threat. It is also one of the principal
components of smog.
Ozone levels are generally higher in summer, during hot sunny weather.
Concentrations are usually highest in late afternoon.
Ozone is a pollutant that can travel large distances. Periods of high
ozone levels can persist anywhere from a few hours to a few days, depending
on weather conditions.
Emission Sources
Although not directly emitted into the air, ozone is produced through a
photochemical transformation of precursor pollutants: nitrogen oxides and
volatile organic compounds. Human activity accounts for most of these
pollutants, including transportation, industry and heating. Since the St.
Lawrence River valley is a natural corridor that drains air masses from the
centre of the continent, ozone levels in Québec are in part attributable to
pollutants emitted in the Great Lakes region of the U.S. and Ontario.
Emissions from Québec urban areas, primarily Montréal and surrounding areas,
also contribute significantly to ozone levels around the province, in
combination with certain weather systems.
Effects on Health and the Environment
Ozone is an oxidizing agent that, at high concentrations, irritates the
nose, throat, skin and eyes. Over short periods of exposure, it can cause
coughing, headaches or breathing problems due to constriction of the airways
and bronchioles. Ozone can weaken a body’s immune defense functions and open
the way to infection. Ground-level ozone is linked to higher numbers of
hospitalizations and emergency room visits for respiratory disorders. People
who play outdoor sports and children may be more prone to the effects of
ozone because their activities are more intense and they spend more time
outdoors. The elderly or people with respiratory ailments may notice their
symptoms worsen. Episodes of high ozone levels usually coincide with heat
waves, which makes people sensitive to pollutants more vulnerable. Over
long-term exposure, the lungs of an adult can become permanently impaired.
Ozone can also damage vegetation and affect crop yields.
Fine Particulate Matter (PM2,5)
Characteristics and Description
Fine particulate matter is airborne microscopic dust and droplets smaller
than 2.5 microns (PM2.5) in diameter. The composition of
particulate matter depends on its source, the season and atmospheric
conditions. Fine particulate matter is comprised primarily of sulfates,
nitrates, carbon, organic substances, ground minerals and metals.
Particulate matter can travel long distances and is a year-round
pollutant common to urban and rural communities. It is a principal component
of smog.
Emission Sources
Particulate matter is generally the product of residential wood burning
(47.5%), industry (32.6%), and transportation (17.1%). Particulates also
form in the air through the chemical reactions of precursor pollutants,
including sulfur and nitrogen oxides. Open sources, such as forest fires,
material and soil erosion, quarries and sandpits, farming and volcanic
eruptions also contribute to particulate matter emissions.
Québec Sources of Particulate Matter (PM2.5)
in 2000 (1)
(1) Excluding open sources such as forest
fires, farming, erosion and volcanic eruptions.
Source: Environment Canada, National
Pollutant Release Inventory, 2004
Effects on Health and the Environment
Because it is so fine, particulate matter less than 2.5 µm in
diameter can penetrate into the deepest recesses of the lungs and remain
there. Short exposures can produce coughing, irritation and bronchial
inflammation. Children and the elderly are particularly sensitive to fine
particulate matter, as are people with asthma, pneumonia, bronchitis,
emphysema or chronic respiratory ailments. Particulate matter is also a
contributing factor to respiratory infections.
In sensitive individuals, fine particulates may also cause
disease and cardiovascular accidents.
Epidemiological health studies reveal that emergency room
visits, hospital admissions and deaths peak during periods when particulate
levels are high. The effects of long-term exposure, which are not as well
documented, show a permanent loss of lung function and higher rates of
cardiovascular and lung cancer deaths.
The characteristics of chemicals in particulate matter are an
important determining factor in their toxicological effect. The presence of
polycyclic aromatic hydrocarbons, dioxins and metals on particulate matter
explains their carcinogenic effect. Recent studies have begun to shed light
on the mechanisms of how fine particulate matter alone or a possible
interaction with other pollutants affects health.
Vegetation is also altered by the deposit of particulates on
leaves, which reduce light absorption and impede photosynthesis. Due to
their composition, particulate matter can also directly attack leaf
structure (necrosis) and affect soil composition. A weakened plant is more
vulnerable to diseases and parasites.
By absorbing and diffusing light, fine particulate matter
creates a type of fog that reduces visibility.
Sulfur Dioxide (SO2)
Characteristics and Description
Sulfur dioxide (SO2) is a colourless gas with an acrid odour
that is generally the product of industry and combustion of fossil fuel
containing sulfur. High levels of this pollutant are found near industrial
sources. Chemical reactions in the atmosphere transform SO2 into
sulfates (liquid or solid form).
Emission Sources
The principal sources of SO2 are industry (88.3%) and
transportation (7.6%). Declines in industrial SO2 emissions over
the last 25 years can be attributed to improved industrial processes and
better filtration systems.
Québec Sources of Sulfur Dioxide (SO2) in
2000 (1)
(1) Excluding open sources such as forest fires.
Source: Environment Canada, National
Pollutant Release Inventory, 2004
Effects on Health and the Environment
SO2 is an irritant gas that acts in combination with other
pollutants, most notably particulate matter. Exposure produces symptoms that
include coughing, reduced lung capacity and aggravated lung and
cardiovascular disease. Asthmatics are particularly sensitive to SO2.
Long-term exposure to SO2 increases the risk of developing a
chronic respiratory illness.
SO2 also contributes to acid rain and the formation of
suspended fine particulate matter.
Nitrogen Dioxide (NO2)
Nature et description
Characteristics and Description
Nitrogen dioxide (NO2) is an irritant gas that is a by-product
of combustion. At high temperatures, airborne nitrogen and oxygen combine to
form nitric oxide (NO), which transforms relatively quickly into NO2.
Both of these substances, NO2 and NO, are the principal
components of the family of nitrogen oxides (NOx). NO2
is responsible for the distinctive brownish colour of smog, reduces
visibility and at high concentrations contributes to the formation of ozone.
Chemical reactions in the atmosphere transform NO2 into nitrates (liquid or
solid form).
Emission Sources
The principal sources of nitrogen oxides are transportation (84.6%) and
industrial burning (10.3%).
Québec Sources of Nitrogen Oxides (NO2) in
2000 (1)
(1) Excluding natural sources such as
bacterial activity, lightening and forest fires.
Source: Environment Canada, National
Pollutant Release Inventory, 2004
Effects on Health and the Environment
Nitrogen dioxide can irritate the lungs, cause coughing and weaken
resistance to respiratory tract infections. In high concentrations, NO2
can cause pulmonary edema. Asthmatics and people with bronchitis are most
sensitive to NO2.
NO2 also contributes to acid rain and suspended particulate
matter.
Carbon Monoxide (CO)
Characteristics and Description
Carbon monoxide (CO) is an odourless, colourless, tasteless gas produced
by the incomplete burning of organic matter, such as fossil fuels (petroleum),
waste and wood. In the atmosphere, it transforms into carbon dioxide (CO2),
a major greenhouse gas. In urban areas, CO readings are highest during peak
rush hour traffic periods, near expressways and other major urban arteries.
Emission Sources
The principal sources of carbon monoxide are transportation (75.7%),
industry (13.5%) and residential wood burning (10.6%).
Québec Sources of Carbon Monoxide (CO) in 2000 (1)
(1) Excluding open sources such as forest fires.
Source: Environment Canada, National
Pollutant Release Inventory, 2004
Effects on Health and the Environment
Carbon monoxide is a toxic pollutant whether at high concentrations
during short periods or at lower concentrations over long periods. It is
absorbed quickly into the bloodstream, where it reduces oxygen intake to
organs and tissues. Smokers and people with cardiovascular disease are
particularly sensitive to CO. Symptoms of exposure include dizziness,
headache, drowsiness, motor and visual impairment, as well as a loss of
dexterity and reflexes. |
