Air pollutants can be visible (e.g., the brownish-yellow colour of smog) or invisible. Besides affecting human health and the environment, air pollutants can also hamper our ability
to see very far (visibility).
Air pollution can have local and regional impacts — such as ground-level
ozone and wood smoke. It can also have wide-reaching, global effects — such as climate change and depletion of the ozone layer.
Health effects from local air pollution can last for a short
while (e.g., coughing) or become a long-term problem (e.g., lung and heart disease, cancer). Pollution can also cause death. An air pollutant can become dangerous to our health when we are exposed to
it for a long time, as well as when we breathe in a large amount of it. For a novel look at how pollutants behave in the air, see the Red-Dye Example.
The Most Significant Air Pollutants
In B.C., the air pollutants that pose the most serious local threat to our health are particulate matter and ground-level ozone — the key ingredients of smog.
They mainly affect the lowest part of the atmosphere, which holds the air we breathe. Particulate matter is a significant
problem in rural areas, as well, due to wood burning.
Particulate Matter (PM)
Particulate matter refers to tiny solid or liquid particles that float in the air. Some particles are large or dark enough to be seen as smoke, soot or dust. Others are so small
that they can only be detected with a powerful, electron microscope. PM occurs in two forms: primary and secondary.
Primary PM is emitted directly into the atmosphere by wood burning (e.g., in wood stoves, open burning, wood stoves) and fossil fuel burning (e.g., in motor vehicles, oil/gas furnaces and
industry). Primary PM also includes pollen, spores and road dust.
Secondary PM is formed in the atmosphere through chemical reactions involving nitrogen dioxide, sulphur dioxide, volatile organic compounds and ammonia.
We measure particulate matter in microns (micrometres). One micron is a millionth of a metre. Particulate matter between 10 and 2.5 microns in diameter or less is called PM10. That’s
about seven times smaller than the width of a human hair. It is invisible to the naked eye and small enough to inhaled into our nose and throat.
Particulate matter that’s 2.5 microns and less is called PM2.5. This is the particulate matter of greatest concern because it can travel
deep into the lungs and become lodged there, causing heart and lung disease, and premature death. Fine particles that comprise PM2.5 are also efficient at scattering light, resulting in a
degradation in visibility. For more information on the health effects of particulate matter, go to How Air Quality Affects Health.
To take a look at a pie chart that shows the sources and relative amounts of PM2.5 in B.C., see "Where Do Air Pollutants Come From?," on the B.C. Air Action Plan, Measuring
Our Progress website
(scroll halfway down the page for the pie chart).
Ground-Level Ozone (O3)
Ground-level ozone is formed by the reaction of two types of chemicals — volatile organic compounds and nitrogen oxide — in
the presence of sunshine and warm temperatures. When the air is still (stagnant), the ozone will build up.
In Canadian cities, ground-level ozone usually occurs in the warmer months of the year. Ground-level
ozone collects over urban areas that produce large amounts of VOCs and NOx. Rural areas can be affected, too, though. That’s because the ozone can travel up to several hundred kilometres
away, carried by the wind.
Low concentrations of ground-level ozone can irritate the eyes, nose and throat. Ozone can also irritate the lung airways, and make them red and swollen (inflammation). People with lung problems are
most at risk, but even healthy people who are active outdoors can be affected when ozone levels are high.
Other Kinds of Air Pollutants
There are many more air pollutants than particulate matter and ground-level ozone. They are usually grouped into four categories, as shown in the table below. For detailed information on all these pollutants,
see Table of Common Pollutants.
Types of Pollutants
|Common Air Contaminants (CACs)
(also known as "criteria air contaminants")
|particulate matter (PM), sulphur oxides (SOx), nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO) and ammonia
Ground-level ozone (O3) is often included with CACs because it is a byproduct of CAC interactions.
|Persistent Organic Pollutants (POPs)
||e.g., dioxins and furans
||e.g., benzene, polycyclic aromatic hydrocarbons(PAHs)