CODES, CRITERIA AND MORE

Last Updated: July 2006

PM₁₀ consists of tiny solid and liquid particles that come from a myriad of sources — both natural and human-caused. "PM" stands for "particulate matter." PM₁₀ particles range in size over many orders of magnitude. They are divided into a fine fraction (less than 2.5 micrometres, called "PM_2.5") and a coarse fraction (2.5-10 micrometres).

Note: The expression "PM₁₀" includes PM_2.5 plus coarse PM. PM_2.5 is a subset of PM₁₀.

The chemical composition of particulate matter is also highly variable, depending on the source of the material. A significant portion is formed by chemical or physical processes in the atmosphere, while other kinds of particles are emitted directly from their source. In short, particulate matter is mixture of particles of many sizes, compositions and origins.

Due to its small size, particulate matter can be inhaled, triggering health problems. Of greatest concern are the smaller particles: PM_2.5. Roughly the size of bacteria, these particles can penetrate deep into the lungs, collecting in the tiny air sacs (called "alveoli") where oxygen enters the bloodstream. To make matters worse, PM_2.5 can remain airborne for extended periods of time. The coarse fraction tends to be less harmful because it settles to the ground quickly and, if inhaled, is removed by the upper respiratory system.

Note: In the early 1990s, the focus was on PM₁₀. More recent research has shifted to the study of PM_2.5 because of its ability to travel farther than PM₁₀ into the human body.

Exposure to high levels of PM_2.5 can play a role in the development of many kinds of lung and heart diseases, including asthma, bronchitis, pneumonia and emphysema. Even more serious, this kind of air pollution is associated with a significant rise in the number of premature deaths. Senior citizens and people who already have lung or heart problems are at risk, but healthy people can also be affected. (For more information, visit the Particulates website.)

Recognizing the threat that particulate matter poses to human health, the ministry chose in 1995 to establish an air quality objective for PM₁₀ before any decision was made on a national objective. In 1997, the Canada-wide Standards process was adopted for establishing national criteria for particulate matter. A Canada-wide Standard for PM_2.5 was subsequently established in 2000. A decision on whether or not to establish criteria for the coarse fraction will be revisited in 2010. In the interim, the provincial PM₁₀ objective provides useful guidance.

The level for PM₁₀is intended to be equivalent to a maximum acceptable level in the national air quality objective system.

Environmental Quality Branch
Ministry of Environment
Government of British Columbia

PO Box 9341
Stn Prov Govt
Victoria, British Columbia
Canada V8W 9M1
http://www.env.gov.bc.ca/air/