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Chapter 4

Other Criteria Contaminants

Characteristics, sources and effects of sulphur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), total reduced sulphur (TRS) compounds and mercury (Hg) are discussed in this chapter, as well as their ambient concentrations for 2000 and trends over time where applicable. Corresponding annual emission estimate trends are also discussed.

SULPHUR DIOXIDE (SO₂)

Characteristics, sources and effects

SO₂ is a colourless gas that smells like burnt matches. It can be oxidized to sulphur trioxide, which in the presence of water vapour is readily transformed to sulphuric acid mist. SO₂ can also be oxidized to form sulphuric acid aerosols. SO₂ is also a precursor to sulphate salts, which are one of the main components of respirable particles in the atmosphere.

Approximately 69 per cent of the SO₂ emitted in Ontario in 2000 came from smelters and utilities (Figure 4.1). Other industrial sources include iron and steel mills, petroleum refineries, and pulp and paper mills. Lesser sources include residential, commercial and industrial space heating. The highest concentrations of SO₂ historically have been recorded in the vicinity of large industrial sources.

Figure 4.1: Ontario Sulphur Dioxide Emissions by Sector

Health effects caused by exposure to high levels of SO₂ include breathing problems, respiratory illness, changes in the lung's defences, and worsening respiratory and cardiovascular disease. People with asthma, chronic lung or heart disease are the most sensitive to SO₂. SO₂ also damages trees and crops. SO₂ and NO_X are the main precursors of acid rain, which contributes to the acidification of lakes and streams, accelerated corrosion of buildings, and reduced visibility. SO₂ also causes formation of microscopic acid aerosols, which have serious health implications and contribute to climate change.

Monitoring Results for 2000

Monitoring for SO₂ was performed at 24 ambient locations in 2000, however, only 23 sites had sufficient data to be used in the analysis presented here. Sarnia recorded both the highest annual mean (10.4 ppb) and the maximum 24-hour concentration (78.1 ppb) during 2000. Science North in Sudbury recorded the highest one-hour concentration (567 ppb). In 2000, the Science North site in Sudbury and the Mississauga site were the only ambient sites to record an instance above the SO₂one-hour criterion of 250 ppb. The SO₂ one-hour criterion was exceeded five times at the Science North site and only one time at the Mississauga site in 2000. However, the 24-hour criterion for SO₂ (100 ppb) was not exceeded at any ambient site in Ontario during 2000.

Figure 4.2: Annual Sulphur Dioxide Means (2000)

Figure 4.2 shows the annual SO₂ means at ambient sites across Ontario. Sarnia and Windsor recorded the highest annual levels in 2000. The annual levels across the province ranged from 0.3 ppb in Thunder Bay to 10.4 ppb in Sarnia. The annual criterion of 20 ppb for SO₂ was not exceeded in 2000.

Trends

As mentioned earlier in the report, over the long term, 1971-2000, Ontario's SO₂ emissions decreased by 82 per cent, while average ambient SO₂levels in the province improved by 83 per cent during the same period. Regulations 346 and 350, control orders on smelting operations and the Countdown Acid Rain program have resulted in significant decreases of SO₂ emissions over the first three years (1991-1994) of the last decade (Figure 4.3). Over the short term, however, SO₂ emissions have remained about the same level since 1994. The annual mean of SO₂ levels over a 10-year period (1991-2000) show a decrease in the early 1990s. However, SO₂ levels increased in 1996 and have remained at a more constant level through to 2000 (Figure 4.4). In 1991, the annual composite mean was 4.1 ppb in comparison to 4.4 ppb in 2000. Despite this small increase of 7.3 per cent over the 10 year period, the annual mean of SO₂ concentrations in 2000 has decreased 4.3 per cent since 1999.

Figure 4.3: Trend of Sulphur Dioxide Emission Estimates (1991-2000)

Figure 4.4: Trend of Sulphur Dioxide Concentrations (1991 - 2000)

Lambton Industry Meteorological Alert (LIMA)

The Lambton Industry Meteorological Alert is covered by the Environmental Protection Act, Regulation 350. Application is limited to that part of the County of Lambton bounded by Lake Huron, the St. Clair River, Highway 80, Moore Township and its continuation through that part of Highway 40, and Lambton County Road 27, which includes Sarnia.

The Minister may declare an alert when the 24-hour running average SO₂ concentration at any station in the LIMA system reaches 70 ppb and meteorological forecasts indicate six hours or more of conditions conducive to elevated SO₂ concentrations. The alert is issued at 70 ppb to prevent levels from reaching the Ontario 24-hour AAQC for SO₂ (100 ppb).

Two monitoring sites are located in Sarnia (Front Street and Centennial Park) and one in Corunna (River Bend).

Seven alerts were issued during 2000. Three of these alerts were based on measurements from the Front Street monitor, another three from the Centennial Park monitor and one alert was based on measurements from River Bend. The highest 24-hour SO₂ running average (105 ppb) was recorded at Front Street and at Centennial Park during the LIMA of February 21 to February 23, and of September 20, 2000, respectively. LIMA alerts called during the past 20 years are shown in Figure 4.5. On average, there have been six alerts called per year since the inception of the program in 1981.

Figure 4.5: Lambton Industry Meteorological Alert (LIMA) Summary (1981 - 2000)

NITROGEN DIOXIDE (NO₂)

Characteristics, sources and effects

NO₂ is a reddish-brown gas with a pungent and irritating odour. It transforms in the air to form gaseous nitric acid and toxic organic nitrates. NO₂ also plays a major role in atmospheric reactions that produce ground-level ozone, a major component of smog. It is also a precursor to nitrates, which contribute to increased respirable particle levels in the atmosphere.

All combustion in air produces nitrogen oxides (NO_X), of which NO₂ is a major component. Approximately 63 per cent of NO_X comes from the transportation sector in Ontario (Figure 4.6). A large part of the remaining 37 per cent comes from fossil fuel power generation, primary metal production and incineration. Natural sources of NO_X include lightning and the aerobic activity of soil bacteria.

Figure 4.6: Ontario Nitrogen Oxides Emissions by Sector

NO₂ can irritate the lungs and lower resistance to respiratory infection. People with asthma and bronchitis have increased sensitivity. NO₂ chemically transforms into nitric acid and, when deposited, contributes to lake acidification. Nitric acid can also corrode metals, fade fabrics, degrade rubber, and damage trees and crops.

Monitoring results for 2000

Monitoring for NO₂ was performed at 30 ambient locations in 2000, however, only 26 sites had sufficient data to be used in the analysis presented here. Etobicoke South recorded the highest annual mean (28.2 ppb) and the highest 24-hour concentration (64.2 ppb) during 2000, whereas Sarnia recorded the highest one-hour concentration (156.0 ppb). Typically, the highest annual NO₂ means are recorded in larger urban centres such as Toronto, Mississauga, and Hamilton, due to their large vehicle fleets (Figure 4.7). The one-hour criterion of 200 ppb for NO₂ and the 24-hour limit of 100 ppb were not exceeded during 2000.

Figure 4.7: Annual Nitrogen Dioxide Means (2000)

Trends

Provincial average ambient NO₂ levels have remained relatively constant over the last decade (1991-2000). Average concentrations in 2000 were 5.7 per cent lower than the levels recorded in 1991(Figure 4.8). Provincial NO_x emissions in 2000 are 8.4 per cent lower than those in 1991 (Figure 4.9). This decrease is attributed to reductions in emissions from the industrial and transportation sectors in the early 1990s. The implementation of Ontario's Drive Clean vehicle inspection program in 1999 has resulted in a decrease of NO_x emissions due to the improvement in vehicle maintenance.

Figure 4.8: Trend of Nitrogen Dioxide Concentrations (1991 - 2000)

Figure 4.9: Trend of Nitrogen Oxides Emission Estimates (1991 - 2000)

CARBON MONOXIDE (CO)

Characteristics, sources and effects

CO is a colourless, odourless, tasteless and at high concentrations, a poisonous gas produced primarily by incomplete burning of fossil fuels. The transportation sector accounts for 65 per cent of all CO emissions from human activity in Ontario (Figure 4.10). A large part of the remaining CO emissions come from primary metal producers (24 per cent) and from fuel combustion in space heating and industrial processes (6 per cent).

CO enters the bloodstream and reduces oxygen delivery to the organs and tissues. People with heart disease are particularly sensitive. Exposure to high levels is linked with the impairment of vision, work capacity, learning ability and performance of difficult tasks.

Monitoring results for 2000

Monitoring for CO was performed at 19 ambient locations in 2000, however, only 18 sites had sufficient data to be used in the analysis presented here. The highest annual mean (1.8 ppm) was recorded at the Toronto West site.

The highest eight-hour measured CO value (5.0 ppm) was recorded at Mississauga while the highest one-hour concentration (11.8 ppm) was measured in downtown Windsor. Highest CO levels are recorded typically in larger urban centres as a result of vehicle emissions (Figure 4.11). The CO one-hour (30 ppm) and eight-hour (13 ppm) ambient air quality criteria have not been exceeded since 1991.

Trends

The trends in provincial averaged one-hour and eight-hour maximum CO concentrations are shown in Figure 4.12 for the period of 1991 to 2000. Over this 10-year period, ambient CO concentrations as measured by the composite average of the one- and eight-hour maximums decreased by 39 and 33 per cent, respectively. The CO composite annual mean in 2000 is 25 per cent less than the corresponding 1991 composite mean. These reductions in ambient CO levels have occurred despite a 20 per cent increase in vehicle-kilometres travelled over the same 10-year period (Figure 4.13).

Provincial CO emissions show a small decline (4.1 per cent) between 1991 and 2000 due to the fleet change to newer vehicles with more stringent emission standards (Figure 4.14). The transportation sector accounts for 65 per cent of the provincial total CO emissions.

TOTAL REDUCED SULPHUR (TRS) COMPOUNDS

Characteristics, sources and effects

TRS compounds produce an offensive odour similar to rotten eggs or cabbage.

Industrial sources of TRS compounds include the steel industry, pulp and paper mills, refineries and sewage treatment facilities. Natural sources include swamps, bogs and marshes.

TRS compounds are not normally considered a health hazard except at very high concentrations. They are, however, a primary cause of odours.

Monitoring results for 2000

Monitoring for TRS compounds was performed at 10 ambient locations in 2000. The highest annual TRS mean (1.2 ppb) was recorded in Oakville during 2000. The maximum one-hour concentration (101 ppb) was measured at the Windsor West site where the greatest number of hours (26) above the AAQC was recorded as well. Elevated TRS levels in Windsor are mainly attributed to trans-boundary impact from nearby sources in Michigan.

 

Trends

The 10-year trend in provincial composite averaged TRS levels at ambient monitoring sites is shown in Figure 4.15. An overall decreasing trend over the 10-year period is evident. Provincial mean ambient TRS levels in 2000 are 33.3 per cent lower than they were in 1991. This decrease is mainly attributed to abatement and regulatory action taken by the ministry over the years.

MERCURY (HG)

Characteristic, sources and effects

Mercury is unique as it is the only metal that is a liquid at room temperature. It is probably best known as the silver liquid in thermometers.

Mercury is of concern as an environmental contaminant because of its ability to accumulate in living organisms, potentially reaching concentrations which could pose a hazard to health in humans and wildlife. The increase of mercury in the aquatic food chain results in relatively high levels of mercury in fish consumed by humans. Although mercury has been recognized as an environmental pollutant for decades, relatively limited monitoring for the assessment and behaviour of mercury in the atmosphere has taken place.

Figure 4.10: Ontario Carbon Monoxide Emissions by Sector

Figure 4.11: Geographical Distribution of One-Hour Maximum Carbon Monoxide Concentrations Across Ontario (2000)

Figure 4.12: Trend of Carbon Monoxide One-Hour and Eight-Hour Maximum (1991 - 2000)

Figure 4.13: Trend of Vehicle-Kilometres Travelled (1991 - 2000)

The sources of mercury deposition in Ontario are transboundary and natural (75%), incinerators (12.5%), thermal generating stations (2.5%), and other sources (10%). Mercury occurs naturally in the environment as mercuric sulphide. It is also present in some fossil fuels.

Potential health effects resulting from exposure to mercury include leukemia and other cancers; reproductive and developmental effects such as impaired development in newborn and young children; and damage to the pulmonary system. Effects of mercury on the aquatic ecosystem are of particular concern as levels bio-accumulate in animals at the top of the food chain resulting in exposure many times higher than directly from water or air.

Monitoring results for 2000

Continuous air monitoring for elemental mercury is relatively new to Ontario's routine air monitoring network. Monitoring for mercury was conducted at two locations, Toronto West and Mississauga, during 2000. The maximum one-hour Hg readings at Toronto West and Mississauga were 50.4 ng/m³ and 27.7 ng/m³, respectively during 2000. These levels are well below the provincial one-hour guideline of 5000 ng/m³. Ninety-nine per cent of the measured one-hour concentrations were less than 6 ng/m³ at both sites.

During 2000, ambient annual levels of mercury were in the 2 ng/m³ range at both monitoring locations. These levels are similar to measurements made at other locations in North America.

Figure 4.14: Trend of Carbon Monoxide Emission Estimates (1991 - 2000)

Figure 4.15: Trend of TRS Concentrations (1991 - 2000)