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Chapter 3

Particles in Ontario's Air

Particulate matter (PM) is the general term used for a mixture of solid particles and liquid droplets found in the air. These particles, which come in a wide range of sizes, originate from many different stationary and mobile sources as well as from natural sources. They may be emitted directly from a source or formed in the atmosphere by the transformation of gaseous emissions. This chapter discusses the ambient monitoring results and trends for the 24-hour (sampling every sixth day) inhalable particles (PM₁₀) network, and the real-time continuous inhalable (PM₁₀) and respirable (PM_2.5) particle network.

Characteristics, sources and effects

Particles include aerosols, smoke, fumes, dust, fly ash and pollen. Composition varies with place and season. Particles in the atmosphere have been characterized according to size mainly because of the different health effects from particles of different diameters. Particles less than 10 microns and 2.5 microns in diameter are defined as inhalable particles (PM₁₀)and respirable particles (PM_2.5), respectively. The smaller the particle size the further the particle will penetrate into the lungs.

PM₁₀ particles are emitted from industrial sources such as fuel combustion, energy production, incineration, construction, mining, metal smelting and processing (Figure 3.1). In the urban airshed, motor vehicle exhaust, residential wood combustion and road dust are the major sources. Natural sources include wind-blown soil, forest fires, ocean spray and volcanic activity. PM_2.5 material is primarily formed from chemical reactions in the atmosphere and through combustion.

The greatest effect on health is from particles 10 microns or less in diameter, which can aggravate bronchitis, asthma and other respiratory diseases. 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 particles. Particles are also responsible for corrosion, soiling, damage to vegetation and reductions in visibility.

As a result of the growing concern for health effects due to inhalable particles, Ontario introduced, in November1997, an interim inhalable particulate (PM₁₀) criterion of 50 µg/m³ on a 24-hour basis. More recently (June 2000), a draft Canada-Wide Standard (CWS) was signed for PM smaller than 2.5 microns (PM_2.5), as they pose the greatest potential for human health effects. The proposed CWS for PM_2.5 uses 30 µg/m³ on a 24-hour basis. These criteria levels will be used as yardsticks for assessing the data in the following discussion.

Figure 3.1: Ontario PM₁₀ Emissions by Sector

[1] Emissions from road dusts, construction, agricultural, etc., are not included.

[2] Emissions from open sources from the smelters are not available.

* Most recent estimates.

Monitoring results for 24-hour inhalable particles (PM₁₀)

Throughout the 1990s and more recently from 1996 to 2000, the ministry has increased monitoring for the smaller fraction (less than 10 microns) of the particulate matter due to growing health concerns, and its association with transboundary pollution. In 2000, Ontario had a total of 43 ambient PM monitors operating across the province, which is more than double the 20 PM monitors operating in 1996.

Twenty-four hour inhalable particles (six-day sampling cycle) are measured by a modified hi-volume (hi-vol) sampler outfitted with a size selective inlet to restrict particle size to less than 10 microns. This is the size range of the particle most likely to be inhaled and deposited into the deepest part of the lung (thoracic region). The daily mass of the inhalable particles is computed from the mass of the collected particles and the volume of air sampled. Quartz fibre filters are used as the filter medium for collection. The filters are also analyzed for metals and sulphate composition. These results are presented in the appendix to this report.

In 2000, 24-hour PM₁₀levels were measured at 25 urban locations. Twelve of the 25 sites monitored ambient levels and will be included in the discussion here. Annual statistics for the remaining 13 sites, which are located in the vicinity of specific sources, can be found in the separate appendix document.

Figure 3.2 shows the distribution of the 24-hour PM₁₀annual geometric means at ambient sites across Ontario.

The two sites recording the highest annual means during 2000 were both located in Windsor. The Windsor Wyandotte Street and Windsor Downtown sites recorded annual means of 26.5 and 26.2 µg/m³ respectively, indicating transboundary impact. The maximum 24-hour concentration (99 µg/m³) was measured in Oakville.

Eight of the 12 ambient PM₁₀ sites recorded exceedances of the 24-hour interim criterion (50 µg/m³) during 2000. The highest percentage of exceedance days (15.8) was recorded at the two sites in Windsor, once again indicating transboundary impact.

Figure 3.2: 24-Hour PM₁₀Annual Geometric Means (2000)

Trends in 24-hour PM₁₀

The provincial trend in 24-hour PM₁₀levels for six ambient urban locations over the past ten years is shown in Figure 3.3. No trend is apparent. However, the highest composite geometric mean (22.1 µg/m³) was measured in 1994 and the lowest mean (18.4 µg/m ³) in 1995 and 1997. The 2000 composite mean was 18.8 µg/m³.

Figure 3.3: Trend of 24-Hour PM₁₀(1991-2000)

Note: Annual composite geometric mean based on 24-h PM10 data for six ambient urban sites over 10 years.

Real-time PM₁₀/PM_2.5 monitoring

In June of 1995, the ministry installed a state-of-the-art continuous (inhalable and respirable) monitoring network of five sites across the province. By 2000, this network had increased in size to a total of 27 ambient sites, 10 PM₁₀ and 17 PM_2.5. Continuous hourly measurements of inhalable and respirable particles are obtained by the Tapered Element Oscillating Microbalance (TEOM) method. The PM₁₀/PM_2.5 monitoring is intended to allow capture of immediate changes in inhalable particle levels in urban communities, near local industries and in areas affected by transboundary sources.

Monitoring results for real-time PM₁₀/PM_2.5

In 2000, monitoring for real-time PM₁₀ was conducted at 10 ambient monitoring locations. The 24-hour statistics for 2000 for the ten locations are shown in Figure 3.4. The annual mean levels for PM₁₀ at the 10 ambient sites ranged from a low of 14.2 µg/m³ in Peterborough to a maximum of 24.2 µg/m³ in Windsor. The highest 24-hour average (79.4 µg/m³) was recorded at the Wm. Merrifield school site in Sault Ste. Marie. The provincial ambient average for PM₁₀ during 2000 was 18.7 µg/m³.

In 2000, continuous monitoring for PM_2.5 was conducted at a total of 17 ambient monitoring locations. Fourteen of the 17 sites recorded sufficient data to be discussed here and their 24-hour statistics are shown in Figure 3.5. The annual mean levels ranged from a low of 8.0 µg/m³in North Bay to a maximum of 15.0 µg/m³ in downtown Hamilton.

The highest 24-hour average (40.4 µg/m₃) was recorded at Toronto North. The provincial ambient average for PM_2.5during 2000 was 11.2 µg/m₃. During 2000, the 98_thpercentile was exceeded at only two locations, Hamilton Downtown and Sarnia.

The geographical distribution of the number of PM₁₀ exceedance days (24-hour concentration greater than Ontario’s interim of AAQC of 50 µg/m3) and PM_2.5 exceedance days (24-hour concentration greater than the proposed CWS of 30 µg/m3) is shown in Figure 3.6. Only five of the ten PM₁₀ monitoring sites recorded exceedance days during 2000. The highest number of exceedance days were recorded in Sault Ste. Marie (12 days) followed by Windsor (9 days), Etobicoke South (4 days), Toronto West and Stouffville (1 day). The number of PM_2.5 exceedance days ranged from 0 in North Bay to 17 in Hamilton. All PM_2.5monitoring sites in southern Ontario recorded at least one exceedance day during 2000.

Figure 3.4: Summary Statistics for 24-Hour PM₁₀ as Measured by TEOM (2000)

Note: Data from ambient sites; TEOM -Tapered Element Oscillating Microbalance.

Figure 3.5: Summary Statistics for 24-Hour PM_2.5 as Measured by TEOM (2000)

Note: Data from ambient sites; TEOM -Tapered Element Oscillating Microbalance.

Figure 3.6: Geographical Distribution of PM₁₀/PM_2.5 Exceedance Days Across Ontario (2000)

Note: Ontario Interim 24-Hour PM10 AAQC is 50 g/m.3µ Proposed Canada-Wide Standard for 24-Hour PM2.5 uses 30 g/m.3µ Ont