Section 5: Air emissions

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Air emissions can have a wide range of effects. For example, traffic emissions affect urban air quality; industrial emissions of sulphur oxides and nitrogen oxides can lead to acid rain; chlorofluorocarbons, hydrochlorofluorocarbons and other substances deplete the ozone layer; and carbon dioxide, methane and nitrous oxide contribute to climate change. Air pollutants have a negative impact on the air we breathe and can also have an effect on soil and water systems through acid deposition. Effects can be local, regional or global, as pollution can travel long distances with prevailing winds.

Criteria air contaminants

Criteria air contaminants (CACs) are those pollutants for which ambient air quality standards have been established by government and include sulphur oxides, carbon monoxide, nitrogen oxides, volatile organic compounds, particulate matter and ammonia. CACs contribute to air quality issues such as smog and acid rain. 1 

Particulate matter

Particulate matter is a broad category of air pollutants that includes a range of small solid or liquid particles varying in size and chemical composition. Total particulate matter (TPM) refers to all particles with a diameter less than 100 micrometres. Particulate matter less than or equal to 10 micrometres (PM10) is a subset of TPM and particulate matter less than or equal to 2.5 micrometres (PM2.5) is a subset of PM102  PM2.5 poses the greatest threat to human health because it can travel deepest into the lungs. 3 

Emissions of TPM increased 45% from 1985 to 2009 while emissions of PM10 increased 19% and emissions of PM2.5 decreased 13% (Chart 5.1). Open sources such as paved and unpaved roads, construction, agriculture and forest fires were responsible for 96% of emissions of TPM, 93% of PM10 and 72% of PM2.5 in 2009 (Table 5.1). Industrial sources were the second highest emitters of PM10, with mining and rock quarrying in particular responsible for a quarter of industrial emissions. Non-industrial sources, residential fuel wood combustion in particular, were the second highest emitters of PM2.5 (see 5.1.7 Air emissions from residential wood consumption).

Sulphur oxides (SOx)

Sulphur oxides (SOx) are a group of gases, consisting mainly of sulphur dioxide (SO2). The combustion of fossil fuels and the smelting of ore are primary sources. 4  SO2 dissolves in water vapour in the air to form acids, and interacts with other gases and particles in the air to form sulphates. 5 

Emissions of SOx decreased 60% from 1985 to 2009 (Chart 5.2). Industrial sources were responsible for more than 64% of emissions of SOx in 2009, with the non-ferrous smelting and refining industry and the upstream petroleum industry responsible for close to three-quarters of industrial emissions (Table 5.1). Electric power generation accounted for 26% of total emissions of SOx in 2009.

Nitrogen oxides (NOx)

Nitrogen oxides are air pollutants that consist primarily of nitric oxide (NO) and nitrogen dioxide (NO2) produced by the reaction of nitrogen (N2) and oxygen (O2) in air at high temperatures in internal combustion engines and furnaces. Nitrogen oxides contribute to the formation of ground-level ozone, the production of particulate matter and acid deposition (including acid rain).

Emissions of NOx decreased 18% from 1985 to 2009 (Chart 5.2). Transportation was the highest emitter of nitrogen oxides, responsible for more than half of emissions in 2009. Industrial sources were the second highest emitters (Table 5.1).

Volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) include those that participate in atmospheric photochemical reactions and exclude methane, ethane, acetone, methylene chloride, methyl chloroform and several chlorinated organics. 6 , 7  VOCs are carbon-containing compounds that have a high propensity to pass from the solid or liquid state to the vapour state under typical environmental conditions. Such compounds contribute to the formation of ground-level ozone, a component of smog as well as the formation of PM2.58 

Emissions of VOCs (excluding natural sources) decreased 26% from 1985 to 2009 (Chart 5.2). Natural sources were responsible for 92% of emissions of VOCs in 2009 while industrial sources and transportation were responsible for the second and third highest emissions (Table 5.1).

Carbon monoxide (CO)

Carbon monoxide is a toxic, colourless, odourless gas generated primarily from the incomplete combustion of fossil fuels. 9 

Emissions of CO decreased 43% from 1985 to 2009 (Chart 5.1). Transportation was responsible for the highest emissions of CO in 2009 (Table 5.1).

Ammonia (NH3)

Ammonia (NH3) is a colourless gas, generated primarily from livestock waste management and fertilizer production. It combines with sulphates and nitrates to form PM2.5 and can also contribute to the nitrification and eutrophication of aquatic systems. 10 

Emissions of NH3 increased 13% from 1985 to 2009 (Chart 5.2). Open sources, agriculture in particular, were responsible for almost 90% of emissions of NH3 in 2009 (Table 5.1).

Air emissions from residential wood consumption

A number of pollutants can be generated from burning wood including particulate matter, nitrogen oxides, carbon monoxide, volatile organic compounds, dioxins and furans, and polycyclic aromatic hydrocarbons. 11 

In 2009, residential fuel wood combustion was responsible for 9% of emissions of PM2.5, the largest contributor after open sources (Table 5.1). Residential fuel wood combustion was also the source of 7% of carbon monoxide emissions in 2009.

The efficiency of wood heating depends greatly on the type of wood fireplace or stove used. Fireplaces tend to use wood inefficiently. Fireplace inserts and airtight wood stoves and heaters are more efficient. In 2007, wood and wood pellets accounted for 13% of total energy used by Canadian households (Table 5.2).

Industrial air pollutant emissions

In 2009, criteria air contaminants made up nearly 99% of air pollutants emitted by industrial facilities according to the National Pollutant Release Inventory (Table 5.3).

The most common substances released to air include sulphur dioxide (1,308,230 tonnes), carbon monoxide (866,724 tonnes) and nitrogen oxides (698,015 tonnes).

In 2008, the majority of capital investments for pollution prevention and abatement and control were targeted at the prevention or reduction of air pollutants. Almost $1.4 billion was invested in pollution abatement and control processes and technologies to reduce air emissions, while capital expenditures on pollution prevention processes and technologies totalled $422.2 million (Table 5.4).

The non-metallic mineral product industry (97%) and the primary metal industry (94%) spent the largest share of their total investments for pollution abatement and control on emissions to air. These two industries also spent the largest share of their total investments for pollution prevention on emissions to air, at 81% and 83% respectively.

Greenhouse gases

Canada's greenhouse gas (GHG) emissions reached 690 megatonnes in 2009, a 17% increase since 1990 (Table 5.5). The increase was driven by growth in emissions from energy, transportation, including road transportation in particular, and mining and oil and gas extraction. GHG emissions declined for the manufacturing industries, industrial processes and the chemical industry over the period. Carbon dioxide (CO2) is by far the most common GHG emitted (Chart 5.3).

In 2009, the largest source of GHG emissions was energy production and consumption activities including direct emissions from fossil fuel combustion, as well as fugitive emissions from coal mining and oil and natural gas activities (Chart 5.4).


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