Sources of NO_x, SO₂ and CO₂ in Canada (1995  data: see Environment Canada)

Nitrogen monoxide, NO, and nitrogen dioxide, NO₂, lumped together as NO_X contribute to both and acidic precipitation and photochemical smog. Sulfur dioxide, SO₂ leads to sulphate pollution and also to acidic precipitation. CO₂ contributes to global warming. In most literature, industrial emissions are reported to be the main sources of SO₂, while the transportation sector is held responsible for most emissions of NO_X. Environment Canada’s web page offers a very detailed view of how various human activities contribute to these forms of pollution, but I focused on the main culprits and constructed a pie chart to hopefully create a simpler overview of the problem.

In reality, you will notice that the transportation sector accounts for a total of only 53% of NOx emissions. Non-diesel automobiles, excluding trucks, contribute only 11% of nitrogen oxides to the atmosphere. A surprisingly large amount comes from the the combustion of diesel fuel for various purposes, and outside of the transportation sector the upstream oil and gas industry makes the most significant contribution.

Smelters and generators, account for more than half of SO₂ emissions, but the combined contribution(26%) of oil and sands, upstream oil and gas and petroleum refining should not go unnoticed.

I often tell my students that cars, cattle and chainsaws are major contributors to global warming. This generalization from James Lovelock is very applicable to Quebec, where stationary combustion of fossil fuels is less of a factor because of nearly exclusive dependency on hydroelectricity. But overall stationary combustion  accounts for nearly half of our Canada's contribution to global warming, which explains why oil-rich Albertans are the most adamant opponents of the Kyoto accord.

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