Primer on Automobile Fuel Efficiency and Emissions - Pollution Probe

TABLE 1-1:
Automobile Tailpipe Emissions
CARBON DIOXIDE (CO 2 )
CO 2 is a greenhouse gas (GHG) that persists in the atmosphere for about 150 years. Due to the large amount of CO 2 emitted
worldwide from the burning of fossil fuels, such as gasoline and diesel, it is the main target of global efforts to reduce atmospheric
concentration levels of GHGs and lessen the negative impacts of climate change. Carbon dioxide is also the most significant
vehicle emission by weight. For each litre of gasoline burned, approximately 2.3 kg of CO 2 is produced (the exact amount
depends on how much carbon and oxygen end up in other combustion products). Less than ideal combustion produces less
CO 2 but more air pollutants, whereas the use of “cleaner” fuels better controlled combustion and exhaust after-treatment technology
reduces air pollution emissions and leads to a minor increase in emission of CO 2 (since more of the carbon in the fuel
ends up bonded with oxygen). For each litre of diesel burned, approximately 2.7 kg of CO 2 is produced. The average car produces
about two to three times its weight in CO 2 every year.
Each year, light-duty vehicles (a category that includes passenger cars, pick-up trucks, SUVs, vans and minivans)
account for roughly 12-13 per cent of CO 2 emissions in Canada. (Source: 2006 Air Pollutant Emissions for Canada, Environment
Canada)
VOLATILE ORGANIC COMPOUNDS (VOCs)
VOCs are defined as “volatile” because they easily and quickly evaporate into the air. There are many thousands of different types
of VOCs emitted into the atmosphere from a range of natural and manmade sources, including those that are harmful and those
that are not. VOCs also react with nitric oxide (NO) and nitrogen dioxide (NO 2) (which are also engine combustion products, see
following page) in the presence of sunlight and heat to form ground-level ozone (O 3). O 3 is considered a by-product of automobile
emissions (and many other non-automobile sources of emissions) and is both toxic and a major component of smog. VOCs
emitted from automobile engines are also referred to as hydrocarbons (HC) because they are primarily uncombusted hydrocarbon
fuels. Gasoline and diesel are complex mixtures of different types of hydrocarbon molecules, some of which are harmful and
can end up in tailpipe emissions, including benzene (H 6C 6) and formaldehyde (HCHO). VOCs such as these can be toxic (even
in small doses), impair brain function or cause cancer.
Another hydrocarbon emitted from automobile engines is methane (CH 4 ), which is not very reactive and hence does not
contribute to smog formation as other types of VOCs do. However, it is a very potent GHG, with more than 20 times the global
warming potential of CO 2 and persists in the atmosphere for approximately 12 years.
In 2006, light-duty vehicles accounted for 0.75 per cent of the total national VOC emissions in Canada.
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Chapter 1 | Emissions from Automobiles