Other Air Pollutants

Nitrogen Dioxide

Nitrogen dioxide is a reddish-brown gas with a pungent odour, which transforms in the atmosphere to form gaseous nitric acid and nitrates. It plays a major role in atmospheric reactions that produce ground-level ozone, a major component of smog. Nitrogen dioxide also reacts in the air and contributes to the formation of PM_2.5 (Seinfeld and Pandis, 2006). All combustion in air produces NO_x, of which NO₂ is a component. Major sources of NO_x emissions include the transportation sector, industrial processes and utilities.

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

There were no exceedances of the provincial one-hour and 24-hour AAQC for NO₂, 200 ppb and 100 ppb, respectively, at any of the monitoring locations in Ontario during 2015. The Toronto West air monitoring station, located in an area of Toronto influenced by significant vehicular traffic, recorded the highest NO₂ annual mean (16.6 ppb) during 2015; whereas Tiverton, a rural site, recorded the lowest NO₂ annual mean (2.4 ppb). The highest NO₂ means were recorded in large urbanized areas, such as the Greater Toronto Area of southern Ontario. The Toronto East station recorded the highest one-hour NO₂ concentration (69 ppb), and both Toronto West and Sudbury recorded the highest 24-hour NO₂ concentration (42 ppb).

The NO₂ annual mean concentrations across Ontario have decreased 32 per cent from 2006 to 2015, as displayed in Figure 10. The NO_x emission trend from 2006 to 2015 indicates a decrease of approximately 38 per cent as shown in Figure 11 (2015 APEI). Ontario’s emissions trading regulations on sulphur dioxide and nitrogen oxides (O. Reg. 397/01 and O. Reg. 194/05) have contributed to the reduction in nitrogen oxides emissions in recent years. Nitrogen oxides emissions from on-road vehicles have also decreased due to the phase-in of new vehicles having more stringent emission standards. The implementation of the Ontario Drive Clean program in southern Ontario in 1999 has also helped further reduce the NO_x emissions from light duty gasoline vehicles.

Figure 10: Trend of NO₂ Annual Means Across Ontario (2006 - 2015)

Note: 10-year trend is a composite mean based on data from 31 monitoring sites.

Figure 11: Ontario NO_X Emissions Trend (2006 to 2015)

Note: Excludes emissions from open and natural resources.

Sulphur Dioxide

Sulphur dioxide is a colourless gas that smells like burnt matches. It can also be oxidized in the atmosphere to form sulphuric acid aerosols. In addition, sulphur dioxide is a precursor to sulphates, one of the main components of airborne secondary PM_2.5. Major sources of SO₂ include smelters, industrial processes and electric utilities.

Health effects caused by exposure to high levels of SO₂ include breathing problems, respiratory illness, and the exacerbation of respiratory and cardiovascular disease. People with asthma, chronic lung disease or heart disease are the most sensitive to SO₂. Sulphur dioxide damages trees and crops. Similar to NO₂, SO₂ leads to the formation of PM_2.5 and is also a precursor to acid rain, which contributes to the acidification of soils, lakes and streams, accelerated corrosion of buildings, and reduced visibility.

Smelters in central Ontario are the major sources of SO₂ emissions in Ontario, accounting for approximately 71 per cent of the provincial SO₂ emissions according to 2015 estimates for point, area and transportation sources (excluding emissions from open and natural sources). Industrial processes (e.g. petroleum refining, cement and concrete manufacturing) accounted for an additional 26 per cent. The transportation sector and miscellaneous sources accounted for the remaining 3 per cent of all SO₂ emissions in the province (2015 APEI).

There were no exceedances of the provincial one-hour, 24-hour and annual AAQC for SO₂ of 250 ppb, 100 ppb and 20 ppb, respectively, at any of the ambient air monitoring locations in Ontario during 2015.   Hamilton Downtown recorded the highest SO₂ annual mean (4.3 ppb) during 2015, and the highest 24-hour maximum concentration (39 ppb) was recorded at Sarnia. Sudbury recorded the highest one-hour maximum concentration (221 ppb) during 2015.

The SO₂ annual mean concentrations from 2006 to 2015 show a decreasing trend of 48 per cent across Ontario in Figure 12. Overall, provincial SO₂ emissions have decreased by approximately 44 per cent from 2006 to 2015 as shown in Figure 13 (2015 APEI). The reduction of SO₂ emissions over the years is the result of various initiatives, which include, but are not limited to,

1. Control orders for Ontario smelters;
2. Countdown Acid Rain program and Canada-wide Acid Rain Strategy;
3. Ontario emissions trading regulations on sulphur dioxide and nitrogen oxides (O. Reg. 397/01 and O. Reg. 194/05);
4. Cessation of coal use in electricity generation; and
5. Low sulphur content in transportation fuels.

Figure 12: Trend of SO₂ Annual Means Across Ontario (2006 - 2015)

Note: 10-year trend is a composite mean based on 10 ambient  air monitoring sites.

Figure 13: Ontario SO₂ Emissions Trend (2006 - 2015)

Note: Excludes emissions from open and natural sources.

Ontario Coal Closure

Ontario was the first jurisdiction in North America to eliminate coal as a source of electricity production, resulting in significant decreases in emissions of NO_x, SO₂ and mercury.

As a result of the introduction of the Cessation of Coal Use Regulation in August 2007, coal went from 25% of Ontario’s energy supply mix in 2003 to zero in 2014 when the last plant ceased coal use. Improvements in SO₂ and NO_x pollution control technologies at operating fossil fuel generating stations also contributed to  reductions during the 1990’s to mid-2000’s. Between the mid-1990’s and 2000’s, SO₂ and NO_x emissions increased because coal-fired power generation capacity was increased to compensate for the lost capacity while the nuclear generating units were refurbished. The coal generating capacity has since been replaced with a mix of emission-free energy sources including  nuclear, hydro and renewables beginning in the early to mid-1990’s, along with lower-emission energy sources such as natural gas and biomass beginning in the late 2000’s. More than 90% of the power generated in Ontario now comes from clean energy.

NO_x Emission Trend from Electric Utilities Ontario

Source of Data: 2015 APEI.

NO_x Emission Trend from Electric Utilities United States

Source of Data: 2015 AMPD and 1990 APETD.

SO₂ Emission Trend from Electric Utilities Ontario

Source of Data: 2015 APEI.

SO₂ Emission Trend from Electric Utilities United States

Source of Data: 2015 AMPD and 1990 APETD.

The U.S. has also reduced emissions from power plants and industrial units over the same period as a result of introducing its Clean Air Markets Programs which targeted SO₂, NO_x and other contaminants by either placing caps on emissions or imposing reduction targets. The first nationwide program was the Acid Rain Program, which was first phased in 1995 and was fully implemented by 2010, followed by the NO_x Budget Trading Program (2003-2008) which was subsequently replaced by the Clean Air Interstate Rule (CAIR) beginning in 2009.

Mercury Emission Trend from Electric Utilities Ontario

Source of Data: 2015 APEI.

Mercury Emission Trend from Electric Utilities United States

Source of Data: 2015 TRI.

Between 1990 and 2015 NO_x emissions from Ontario’s electricity sector (including coal, natural gas, fuel oil, diesel and biomass generating stations) decreased by 87.8% and SO₂ emissions decreased by 99.8%, and mercury emissions decreased by 95.3% between 2000 and 2015; due in part to the elimination of coal. By comparison, for the same periods, NO_x emission from the electricity sector in the U.S. decreased by 79.5%, SO₂ by 85.9% and mercury by 68.2%.

Further, a comparison of the emission reductions attributable to coal elimination as compared to overall provincial emission reductions, illustrates the significance of coal cessation – coal plant NO_x emission reductions were 24% of provincial total, SO₂ was 22% and mercury was 29%.

Pollutant	Ontario Emission Reductions	Coal Plants Emission Reductions	Coal Plant Emissions Reductions relative to Ontario
SO2	↓ 878 kt	↓ 193 kt	22%
NOx	↓ 313 kt	↓ 75 kt	24%
Mercury	↓ 1897 kg	↓ 549 kg	29%

Notes:
Excludes emissions from open and natural sources.
NO_x and SO₂ emission reductions are based on 1990-2015 data.
Mercury emission reductions are based on 2000-2015 data.

Carbon Monoxide

Carbon monoxide is a colourless, odourless, tasteless and, at high concentrations, poisonous gas. This gas can enter the bloodstream and reduce oxygen delivery to the organs and tissues. People with heart disease are particularly sensitive to CO. Exposure to high CO levels is associated with the impairment of vision, work capacity, learning ability and performance of complex tasks. Carbon monoxide is produced primarily by the incomplete combustion of fossil fuels. The 2015 estimates for point, area and transportation sources (excluding emissions from open and natural sources) indicate that the transportation sector accounted for 66 per cent of all CO emissions (2015 APEI).

In 2015 there were no exceedances of the provincial one-hour and eight-hour AAQC of 30 parts per million (ppm) and 13 ppm, respectively, at any of the ambient air monitoring locations in Ontario. Windsor Downtown recorded the highest one-hour CO maximum of 1.91 ppm and the highest eight-hour maximum of 1.20 ppm. Typically, higher CO concentrations recorded in urban centres are attributable to vehicle emissions.

The composite means of the one-hour and eight-hour CO maximums have decreased 53 per cent and 41 per cent, respectively, across the province from 2006 to 2015. Carbon monoxide emissions have been reduced by approximately 32 per cent from 2006 to 2015 (2015 APEI).