Airborne particulate is the general term used to describe a mixture of microscopic solid particles and liquid droplets suspended in air. Particulate matter (PM) includes aerosols, smoke, fumes, dust, fly ash and pollen. Its composition is complex and varies with origin, residence time in the atmosphere, time of year and environmental conditions. Particulate matter is classified according to its size, since different health effects are associated with particles of different diameters. Fine particulate matter, denoted as PM2.5, is less than 2.5 micrometres in diameter, approximately 30 times smaller than the average diameter of a human hair.

Fine particulate matter can have various negative health effects, especially on the respiratory and cardiovascular systems. Particulate matter increases respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing. People with heart or lung disease, children and older adults are particularly sensitive to this pollutant.

Fine particulate matter consists of primary and secondary PM2.5. Primary PM2.5 is emitted directly to the atmosphere. Major sources of primary PM2.5 include residential fireplaces and wood stoves, motor vehicles, smelters, power plants, industrial facilities, and agricultural burning and forest fires. Secondary PM2.5 is formed indirectly in the atmosphere through a series of complex chemical reactions of gaseous precursors, and it includes nitrate, sulphate, and organic matter. Higher nitrate levels are common in the cooler months whereas sulphates are more elevated during warmer months.

The 2017 estimates for Ontario’s PM2.5 emissions from point, area and transportation sources (excluding emissions from open and natural sources) indicate that residential fuel combustion accounted for 56% of the total PM2.5 emissions, as shown in Figure 4. The major contributor to residential emissions is fuel wood combustion in fireplaces and wood stoves. Industrial processes and the transportation sector accounted for 18% and 13%, respectively (Air Pollutant Emission Inventory 1990-2017, 2019).

In 2017, all 39 of the Ministry’s AQHI air monitoring stations measured PM2.5. PM2.5 annual mean concentrations ranged from 4.1 μg/m3 in Petawawa to 8.5 μg/m3 in Windsor and Hamilton. The PM2.5 24-hour maximum concentrations ranged from 13 μg/m3 in North Bay to 38 μg/m3 recorded at Burlington. Five air monitoring stations (Windsor Downtown, Windsor West, Sarnia, Burlington and Barrie) measured daily averages above the 24-hour PM2.5 reference level of 28 μg/m3; this occurred on only one occasion at each of the five air monitoring stations. A summary of the 2017 PM2.5 annual statistics for individual AQHI air monitoring stations in Ontario are presented in Table A5 of the Appendix.

Figure 4: Ontario PM2.5 emissions by sector (2017 estimates for point/area/transportation sources)

Ontario’s fine particulate matter emissions by sector based on 2017 estimates for point/area/transportation sources.

Residential: 56%, miscellaneous: 13%, other industrial sources: 9%, other transportation: 8%, smelters/primary metals: 8%, road vehicles: 5%, cement and concrete industry: 1%.

Note: Excludes emissions from open and natural sources.

In 2013, as part of a national initiative funded by Environment and Climate Change Canada, Ontario replaced its Tapered Element Oscillating Microbalance (TEOM) PM2.5 monitors with the Synchronized Hybrid Ambient Real-time Particulate (SHARP) instrument across its ambient air monitoring network and started reporting with this new technology. While annual means and maximums are reported for 2017, 10-year trends for the entire ambient air monitoring network cannot be determined since the 2013 to 2017 PM2.5 dataset is not directly comparable to data collected using the older technology. It is however possible to apply a correction factor to the TEOM data to generate an approximate 10-year trend (Su et al, 2018). Applying the approximate correction factor to the TEOM data shows an 11% decrease in PM2.5, from 2008 to 2017 as shown in Figure 5. PM2.5 10-year trends for individual AQHI air monitoring stations in Ontario are presented in Table A13 of the Appendix.

Provincial PM2.5 emissions have decreased approximately 16% from 2008 to 2017 as shown in Figure 6. The decrease is attributed to reductions of PM2.5 emissions from electric power generation, industry and transportation. Fine particulate matter emissions from electric power generation and industrial processes have been reduced approximately 30% during this period. Emissions from the transportation sector decreased 45% with the phase-in of new vehicles/engines having more stringent emission standards over the same period (Air Pollutant Emission Inventory 1990-2017, 2019).

Figure 5: Trend of PM2.5 annual means across Ontario (2008-2017)

Line graph showing the trend of fine particulate matter composite means for 39 ambient air monitoring stations across Ontario from 2008 to 2017.

Data shows an 11% decrease in fine particulate matter from 2008 to 2017.

10-year trend based on data from 39 ambient air monitoring stations.
A correction factor was applied to PM2.5 concentrations measured by TEOM (2008-2012) to approximate SHARP-like measurements. PM2.5 concentrations measured by SHARP are reflected from 2013 and onward.
Ontario does not have an annual AAQC for PM2.5 .

Figure 6: Ontario PM2.5 emission trend (2008-2017)

Stacked column chart displaying the Ontario fine particulate matter emissions trend from 2008 to 2017.

Provincial fine particulate matter emissions have decreased approximately 16% from 2008 to 2017.

Note: Excludes emissions from open and natural sources.