Definitions
The Primer on Automobile Fuel Efficiency and Emissions mentions numerous scientific terms, concepts, and objects. This page provides additional information and definitions of these various items.
Acid Rain
Carbon Monoxide (CO)
Carbon Dioxide (CO2)
Criteria Air Contaminants (CACs)
Fuel economy
Fuel consumption
Greenhouse effect
Oxides of Nitrogen
Oxides of Sulphur (Sox)
Particulate Matter (PM)
Smog
Volatile Organic Compounds (VOCs)
Acid Rain – Regular rain becomes acid rain because of pollutants that humans (and some natural processes) have released into the air. Two pollutants in particular are the main cause of acid rain: sulphur dioxide (SO2) and oxides of nitrogen (NOx). These pollutants are both emissions that come out of a vehicle’s tailpipe. The rain becomes so acidic that it damages the environment when it falls to Earth.
Carbon Monoxide (CO) – CO is a colourless, odourless gas that is poisonous, and forms in the engine as a result of incomplete combustion. In the human body, CO reduces the ability of the blood to carry oxygen from the lungs. Everyone’s health is threatened by this potentially lethal emission, but people with heart disease are most vulnerable to its effects. Other high risk groups include pregnant women (and their fetuses), infants, children, the elderly and people with anemia and respiratory or lung disease. In 2006, light-duty vehicles accounted for 34 per cent of the total national CO emissions in Canada.
Carbon Dioxide (CO2) – CO2 is a greenhouse gas (GHG) that persists in the atmosphere for about 150 years. Due to the large amount of CO2 emitted worldwide from the burning of fossil fuels, such as gasoline and diesel, it is GHGs that are the main target of global efforts to reduce atmospheric concentration levels and lessen the negative impacts of climate change. Carbon dioxide is also the most significant vehicle emission by weight. The average car produces about two to three times its weight in CO2 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 CO2 emissions in Canada.
Criteria Air Contaminants (CACs) – CACs are a group of chemical compounds produced by automobiles that can seriously affect human health. These emissions are either toxic, contribute to the formation of smog, or both, and are also referred to as air pollutants. These include NOx, VOCs, CO, SOx, and PM.
Fuel economy – miles driven per gallon consumed
Fuel consumption – litres consumed per hundred kilometers
Greenhouse effect – the “natural greenhouse effect” is what allows life on earth to thrive. Certain chemical compounds in the Earth’s atmosphere act as ‘greenhouse gases’, absorbing energy that is reflected off of the earth’s surface and trapping some of the heat in the atmosphere, which then warms the Earth’s surface to an average of 14°C. However, any changes in the atmospheric greenhouse gas concentrations will affect the amount of energy stored in the atmosphere and disrupt the balance of the global climate system. When the amount of carbon dioxide is increased, more heat is trapped in the atmosphere, causing an “enhanced greenhouse effect” that causes the Earth’s surface temperature to rise even further.
Oxides of Nitrogen – Under the high pressure and temperature conditions of a typical engine, nitrogen and oxygen in the air (that is drawn into the engine) combine to form NOx. Fuel is not directly the cause of NOx formation, but rather it is the heat produced by the combustion of the fuel that leads nitrogen and oxygen to bond. The chemical arrangements of NOx include nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). NO and NO2 are air pollutants while N2O is a potent greenhouse gas. NO and NO2 react with VOCs in the presence of sunlight and heat to form ground-level ozone (O3) and play a part in the formation of fine particulate matter, or PM (discussed on following page). They can also combine with water vapour to form nitric acid, which contributes to acid rain.
NO2 irritates the lungs, impairs lung function (even with short term exposure) and lowers resistance to respiratory infection. In children and adults with respiratory disease, NO2 can cause symptoms including coughing, wheezing and shortness of breath. In itself, N2O does not contribute to poor air quality, but it is a potent GHG. With roughly 300 times the global warming potential of CO2, N2O persists in the atmosphere for about 100 years. In 2006, light-duty vehicles accounted for 8 per cent of the total national NOx emissions in Canada.
Oxides of Sulphur (Sox) – Under the high pressure and temperature conditions of a typical automobile engine, sulphur in the fuel and oxygen from the air combine to form SOx. The chemical arrangement of primary concern is sulphur dioxide (SO2). SO2 contributes to the formation of fine PM and therefore is a smog pollutant. Exposure to SO2 leads to eye irritations, shortness of breath, and impaired lung function. Combining with water molecules to form sulphuric acid, SO2 is one of the more persistent pollutants and is a major source of acid rain, acid snow, and acid fog that impact ecosystems and urban environments. SOx can also interfere with the proper functioning of a vehicle’s emissions aftertreatment system (i.e., catalytic converter) and, as a result, reduce its ability to decrease other harmful emissions such as HC, CO and NOx. In 2006, light-duty vehicles accounted for less than 0.1 per cent of the total national SOx emissions in Canada.
Particulate Matter (PM) – PM is emitted directly from automobile tailpipes as microscopic carbon residues (a product of fuel combustion) and as liquid droplets. Particles are measured by their diameter and range in size from 0.005 to 100 microns (one micron equals one thousandth of a millimetre or 1/50 of the width of an average human hair). Some PM is visible, such as the black smoke often seen in diesel truck exhaust. These particles can be large enough to become trapped in the body’s filters that are the nose and throat, limiting the potential health threat. Smaller particulates, measuring less than 10 microns (PM10), are invisible and can be breathed into the lungs. Particulates that measure less than 2.5 microns (PM2.5) are able to penetrate deep into the lungs. The smaller the particle, the deeper it may enter the lungs and theoretically, the greater the damage it can cause. The toxicity and carcinogenic effect of PM can vary according to its source and composition. Other toxic chemicals can adhere to fine PM, compounding the threat as they are carried deep into the lungs where they can pass into the bloodstream. According to the Ontario Medical Association, studies have shown that fine PM is linked to cardiac disease and can trigger heart attacks. PM is also a component of smog and is suspected to have a secondary impact on global warming trends as it reflects, absorbs and scatters solar radiation. In 2006, light-duty vehicles accounted less than 0.5 per cent of the national PM2.5 and PM10 emissions in Canada.
Smog – Smog is formed in the lower atmosphere, just above the Earth’s surface when a variety of sources release smog forming pollutants (PM, NOx, VOCs, SO2 and CO) into the air. Heat and sunlight cause chemical reactions to occur between these pollutants, forming ground-level ozone (O3) – a major component of smog. When inhaled, smog can be harmful to human health. The damaging short‐term effects can range from eye, nose or throat irritation to decreased lung function. Smog can also aggravate respiratory or cardiac disease and, in some cases, cause premature death. Recent health studies suggest that there is no safe level of human exposure to smog and negative health outcomes are associated with very low levels of exposure, even for healthy individuals. The Ontario Medical Association estimates that more than 9,500 people in Ontario die prematurely each year from the effects of smog. Furthermore, every year, about 16,000 people in Ontario are admitted to hospital as a result of exposure to smog and an additional 60,000 sufferers visit the emergency room. Aside from their contribution to smog formation, some of these pollutants can have direct, negative impacts on human health, and are therefore called air toxics.
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 (NO2) in the presence of sunlight and heat to form ground-level ozone (O3). O3 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 (H6C6) 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 (CH4), 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 CO2 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.
Everything you ever wanted to know about fuel efficiency appears in our Primer on Automobile Fuel Efficiency and Emissions. Take a look for yourself! 