Fine Particulate Matter

What is fine particulate matter?

Particulate matter is characterized according to size - mainly because of the different health effects associated with particles of different diameters. Particulate matter is the general term used for a mixture of solid particles and liquid droplets in the air. It includes aerosols, smoke, fumes, dust, ash and pollen. The composition of particulate matter varies with place, season and weather conditions. Fine particulate matter is particulate matter that is 2.5 microns in diameter and less. It is also known as PM2.5 or respirable particles because it penetrates the respiratory system further than larger particles.

PM2.5 in Ontario is largely made up of sulphate and nitrate particles, elemental and organic carbon and soil.

What are the sources of fine particulate matter?

PM2.5 material is primarily formed from chemical reactions in the atmosphere and through fuel combustion (e.g., motor vehicles, power generation, industrial facilities, residential fire places, wood stoves and agricultural burning). Significant amounts of PM2.5 are carried into Ontario from the U.S. During periods of widespread elevated levels of fine particulate matter, it is estimated that more than 50 per cent of Ontario's PM2.5 comes from the U.S.

Ontario PM2.5 Emissions by Sector
(Emissions from Point/Area/Transportation Sources, 2006 Estimates)
PM 2.5 Composition/Emissions pie chart
Category Percent
Residential 34%
Transportation 24%
Other Industrial Processes 21%
Smelters/Primary Metals 12%
Miscellaneous 6%
Pulp and Paper 3%

Note: 2006 is the latest complete inventory. Emissions may be revised with updated source/sector information or emission estimation methodologies as they become available.

Approximately 34 per cent and 24 per cent of PM2.5 emitted in Ontario in 2006 came from residential and transportation sectors, respectively, while other industrial processes accounted for 21 per cent. Lesser sources of PM2.5 include smelters/primary metals, miscellaneous, and pulp and paper.

What are the effects of fine particulate matter?

The greatest effect on health is from particles 2.5 microns or less in diameter. Exposure to fine particulate matter has been associated with hospital admissions and several serious health effects, including premature death. People with asthma, cardiovascular or lung disease, as well as children and elderly people, are considered to be the most sensitive to the effects of fine particulate matter. Adverse health effects have been associated with exposure to PM2.5 over both short periods (such as a day) and longer periods (a year or more).

Fine particulate matter is also responsible for environmental effects such as corrosion, soiling, damage to vegetation and reduced visibility.

The following table shows the health effects of different AQI levels caused by fine particulate matter.

Health effects of different Air Quality Index (AQI) levels caused by fine particulate matter
Category AQI Pollutant Concentration
Breakpoints (µg/m3)
Fine Particulate Matter (PM2.5)
Very Good
Very Good
0 - 15
0 - 11
Sensitive populations may want to exercise caution.
16 - 31
12 - 22
Sensitive populations may want to exercise caution.
32 - 49
23 - 45
People with respiratory disease at some risk.
50 - 99
46 - 90
People with respiratory disease should limit prolonged exertion; general population at some risk.
Very Poor
100 or over
91 or over
Serious respiratory effects even during light physical activity; people with heart disease, the elderly and children at high risk; increased risk for general population. 

Note: The AQI sub-index for PM2.5 is based on a 3 hour running average concentrations.
           µg/m3 = micrograms per cubic metre.