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Chapter 7

The Great Lakes Basin Area: An Air Quality Perspective

The purpose of this section is to compare the state of air quality in selected cities within the Great Lakes Basin (GLB) area. Air quality levels for the year 2000 and for the 10-year period 1991-2000 were compared for nine cities: five in Ontario (Toronto, Hamilton, London, Windsor and Thunder Bay) and four in the U.S. (Chicago, Cleveland, Detroit, and Minneapolis-St. Paul), as displayed in Figure 7.1. The city populations ranged from 125,000 (Windsor) to 7.5 million (Chicago). The pollutants considered in the comparison were the five criteria contaminants: ozone, inhalable particles, nitrogen dioxide, carbon monoxide and sulphur dioxide.

Figure 7.1: Selected Sites in the Great Lakes Basin Area

Data were used from all available monitoring sites within the metropolitan statistical areas of each city (where applicable) to represent average city air quality. The inter-city comparisons represented here are referenced to ambient air quality criteria (AAQC) for Ontario and the national ambient air quality standards (NAAQS) for the United States.

GROUND-LEVEL OZONE (O₃)

Monitoring results for 2000

The highest one-hour O₃ concentration during 2000 was recorded in Detroit (115 ppb) followed closely by London and Cleveland, each recording a maximum of 110 ppb. Thunder Bay recorded the lowest O3 maximum at only 73 ppb, while Hamilton recorded the second lowest O₃ maximum of 93 ppb. The U.S. NAAQS (120 ppb) was not exceeded by any of the nine cities examined in the GLB area in 2000, however, eight of the cities did exceed the more restrictive Ontario one-hour AAQC (80 ppb) with the exception of Thunder Bay.

Trends

The ten-year range (1991-2000) for one-hour maximum O₃ concentrations in the selected nine cities of the GLB area is shown in Figure 7.2. Windsor, due to its close proximity to the U.S. border, is at the higher end of the scale along with Detroit and Chicago. At the lower end of the scale is Thunder Bay followed by Minneapolis-St. Paul, London and Hamilton.

In addition to the year-to-year variability in meteorological factors, which are conducive to high ozone concentrations during episode events, the combination of local emissions and long-range transport of pollution from the United States greatly influence the magnitude of O₃ concentrations recorded in southwestern Ontario, such as those experienced in Windsor, Toronto, Hamilton and London.

Figure 7.2 Range of Maximum One-Hour Ozone Concentrations in the
Great Lakes Basin Area (1991 - 2000) 

INHALABLE PARTICLES (PM₁₀)

Monitoring results 2000

The highest composite annual PM10 mean for 2000 was recorded in Cleveland (37.7 µg/m³), followed by Detroit (32.5 µg/m³). The U.S. NAAQS of 50 µg/m3 was not exceeded by any of the nine cities examined in the GLB area in 2000. Thunder Bay recorded the lowest composite annual mean (13.2 µg/m³). Overall, when comparing composite annual means of PM₁₀ during 2000, the Canadian cities recorded concentrations ranging from 13.2 µg/m³ to 24.2 µg/m³, whereas the American cities recorded levels from 25.0 µg/m³ to 37.7 µg/m³.

Trends

The 10-year range (1991-2000) in composite annual PM₁₀ means for the nine selected cities in the GLB area is shown in Figure 7.3. Cleveland's levels were at the higher end of the range of composite annual means reported. As well, Cleveland was the only city that exceeded the U.S. NAAQS of 50 µg/m³ between 1991-2000. Thunder Bay reported the lowest composite annual mean over the 10-year period, followed closely by London. Similar to the composite annual means in 2000, the American cities dominated the higher end of the scale whereas the Canadian cities were at the lower end of the scale over the 10-year range.

PM₁₀may be directly emitted by a source or formed in the atmosphere by the transformation of gaseous precursor emissions, such as NO_X and SO₂. Long-range transport of these precursors from the mid-western states of the U.S. contribute to the PM levels in south-western Ontario, as well as local emissions from human activity and natural sources.

Figure 7.3: Range of Composite Annual PM₁₀ Means in the
Great Lakes Basin Area (1991 - 2000)

NITROGEN DIOXIDE (NO₂)

Monitoring results for 2000

The highest composite annual NO₂ means for 2000 were recorded in Toronto (24 ppb) and Chicago (23 ppb). Thunder Bay recorded the lowest composite annual mean for NO₂ (12 ppb) in 2000 followed by London at 17 ppb. Overall, none of the nine cities exceeded the U.S. NAAQS for NO₂during 2000.

Trends

The 10-year range of composite annual NO₂ means for the nine cities in the GLB area is presented in Figure 7.4. Toronto, Cleveland, Chicago and Windsor share similar means at the higher end of the range, while Thunder Bay is at the lower end.

Higher levels of NO₂are found in larger urban centres such as Toronto, Cleveland and Chicago because of population density and motor vehicle emissions.

Figure 7.4: Range of Composite Annual Nitrogen Dioxide Means
in the Great Lakes Basin Area (1991 - 2000)

CARBON MONOXIDE (CO)

Monitoring results for 2000

The highest one-hour CO concentrations during 2000 were recorded in Cleveland (12.8 ppm) and Windsor (11.8 ppm). Nonetheless, the levels remained well below the Ontario AAQC of 30 ppm and the U.S. NAAQS of 35 ppm. London recorded the lowest one-hour CO maximum at 2.5 ppm.

Trends

The 10-year range (1991-2000) in maximum CO concentration for the nine cities examined in the GLB area is shown in Figure 7.5. Cleveland and Minneapolis-St. Paul were at the higher end of the scale, while Thunder Bay and London were at the lower end.

Highest CO levels are recorded typically in larger urban centres and are strongly influenced by local vehicle emissions. 

Figure 7.5: Range of Maximum One-Hour Carbon Monoxide Concentrations
in the Great Lakes Basin Area (1991 - 2000)

SULPHUR DIOXIDE (SO₂)

Monitoring results for 2000

The highest composite annual SO₂mean was recorded in Windsor (7.5 ppb), while Thunder Bay recorded the lowest composite annual mean (0.0 ppb) in 2000. All of the cities examined in the GLB area recorded levels well below the Ontario AAQC of 20 ppb and the U.S. NAAQS of 30 ppb.

Trends

The 10-year range (1991-2000) of composite annual SO₂ means for the nine cities in the GLB area are displayed in Figure 7.6. Cleveland was at the higher end of the range of annual means reported with Windsor, while Thunder Bay was at the lower end.

Figure 7.6: Range of Composite Annual Sulphur Dioxide Means
in the Great Lakes Basin Area (1991 - 2000)

RANKING OF SELECTED CITIES IN THE GREAT LAKES BASIN AREA

The levels for the criteria pollutants (O₃, PM₁₀, NO₂, CO and SO₂) were examined for the 10-year period (1991-2000) in Chicago, Cleveland, Detroit, Minneapolis-St. Paul, Hamilton, London, Thunder Bay, Toronto and Windsor, and subsequently ranked accordingly in order to collectively compare the air quality within the nine selected cities.

The ranking of the cities (based on the concentration of the pollutant measured in the ambient air) ranged from 1 (representing the best air quality) to 9 (representing the poorest air quality). The rankings, based on a 10-year average, were summed up for each city resulting in a total score. The higher the total score, the worse the air quality.

The overall ranking of the nine cities in the GLB area for the criteria pollutant levels for 1991-2000 is displayed in Table 7.1. Thunder Bay placed first representing the best air quality in the region, whereas Cleveland placed ninth recording the overall highest concentrations of the criteria pollutants examined in the area. However, the state of air quality is significantly impacted by population density, industrial base and the geographical location of the cities within the study area. These factors must be considered as they consequently influence the ranking.

Table 7.1: Ranking of Cities in the Great Lakes Basin Area According to Criteria Pollutant Levels (1991-2000)
City	O3	PM10	NO2	CO	SO2	Total Score	Overall Ranking
Thunder Bay	1	1	1	2	1	6	1
London	3	2	4	1	3	13	2
Minneapolis-St. Paul	2	6	2	8	2	20	3
Hamilton	4	4	5	4	5	22	4
Toronto	5	3	9	6	4	27	5
Windsor	7	5	6	3	8	29	6
Detroit	9	7	3	7	7	33	7
Chicago	8	8	7	5	6	34	8
Cleveland	6	9	8	9	9	41	9
Individual rankings are summed for each city to determine a total score.