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Above: A smoggy view of Montréal, Québec from the Saint Joseph's Oratory. Source:Wikimedia Commons.

Vehicles are pretty useful. Besides getting you from point A to point B, they can carry stuff, they can carry other people, and they can go further more quickly than your own two feet. They are also quite good at other things that might not come as easily to mind, like contributing to smog and climate change. If you've ever been stuck in traffic behind a big heavy truck, you've no doubt smelled the noxious gases spewing out. Even when you can't smell anything, vehicles emit all sorts of nasty stuff that can have less than positive effects on people and the planet.


We all know that most cars and trucks run on fuel. Although some vehicles now also run on electricity, more often than not, most run on fossil fuels, like gasoline or diesel which are burned inside an engine. That's why it's called an internal combustion engine – combustion is basically a specific term for burning. In a car's engine, fuel is put into a small, enclosed space and then ignited. This ignition releases a large amount of energy in the form of rapidly expanding gases (i.e., an explosion). By setting off hundreds of these explosions every minute, a car's engine is able to move pistons up and down, which in turn is converted into rotational motion by the crankshaft that moves the car. The gases, which we call exhaust, then leave the engine through the car's exhaust pipe (tailpipe) and muffler. These vehicle exhaust emissions can affect air quality (a measure of the amount of pollutants in the air) both down near the Earth's surface where we live and breathe as well as high in the atmosphere.


Smog is a type of localized, short-duration air pollution that occurs near ground level. You can recognize a very smoggy day by the haze that hangs in the air. Historically, the word "smog" was used to describe the thick, grayish haze that occurred when smoke and fog mixed together. Today, the word smog is used to describe a type of air pollution that is mix of certain types of gases and particles that we can see both in the summer and in the winter (see Figure 1).

Vehicle emissions are one of the primary contributors to smog, which is mainly made up of particulate matter (PM) and ground level ozone (O3). Fuel combustion emits tiny bits of soot called particulate matter. This is the black gunk that accumulates on snow in winter. PM mainly comes from the incomplete combustion of fuel in engines, but it can also come from burning coal and wood. Incomplete combustion releases carbon monoxide (CO) as well as unburned fuel which can become part of smog.

In addition to the direct products of combustion, there are the indirect products of combustion such as nitrogen monoxide and nitrogen dioxide (together referred to as NOx) which are formed when nitrogen and oxygen from air combine due to the heat released during combustion. Other indirect products include volatile organic compounds (VOCs) such as benzene and formaldehyde which are found naturally in crude oil and gasoline, as well as sulfur dioxide ( SO2), which comes from the combustion of diesel fuel.

The other important ingredient in smog is ground level ozone. You may have heard of ozone as something that is found in the upper atmosphere. There ozone up there plays a very important role. Ozone in the atmosphere protects us from harmful ultraviolet (UV) radiation. Unfortunately, this 'good' ozone is slowly being depleted by human-made chemicals. Ground level ozone, unlike ozone in the atmosphere, is not 'good' ozone. The ozone at ground level is formed when NOx and VOCs react together in the presence of sunlight when the air is still. This is why we tend to have smog on hot summer days, although smog can also occur in winter, particularly when there are a lot of vehicle emissions.

On smoggy days, it can seem as though it's a lot harder to breathe properly. That's not your imagination – smog has been linked to thousands of premature deaths every year in Canada, not to mention increased hospital visits due to reduced lung function, aggravated asthma, and other respiratory illnesses. Children, the elderly and people who exercise are most at risk from smog-related health effects. Nature isn't immune either. When NO x and SO2 react with water in the atmosphere, they form acid precipitation in the form of rain and snow. Acid rain can affect the productivity of plants and cause lakes and rivers to become acidic, killing or preventing the reproduction of some species, thus affecting whole ecosystems.

Climate Change and Greenhouse Gases

You may never have thought about it this way before, but the Earth is actually covered in a blanket – we call this blanket the atmosphere. Relative to the planet's size, this blanket is astoundingly thin. If the Earth were the size of an apple, the atmosphere would be the thickness of the skin of the apple. Though thin, the atmosphere is really good at keeping the planet warm. Without it, the average temperature on Earth would be a frozen -18°C instead of the present (and life giving) 14°C. This warming (also known as global warming) happens due to greenhouse gases (GHGs), which are gases in the atmosphere that have heat-trapping properties. When the sun's rays strike the Earth the surface is heated. This heat rises and radiates away from the surface. GHGs prevent some of the heat (infrared radiation) from escaping back out to space (greenhouse effect). Greenhouse gases are a type of global, long-term air pollution that occurs in the upper atmosphere.

The problem that we are facing today is that we are pumping way too many GHGs into the atmosphere – meaning that the blanket is, in a sense, getting thicker, making the planet hotter and the weather more extreme (anthropogenic greenhouse effect). Before the industrial revolution, the concentration of carbon dioxide (CO2) in the atmosphere was 280 parts per million by volume (ppmv). Today it is at 400 ppmv, which is higher than it has been in over 650 000 years, and that number is continuing to go up. This excessive concentration of GHGs is what scientists believe is the cause of what is known as climate change. The Earth was about 0.75°C warmer in the last century (100-year trend 1906–2005). This may not sound like that much, but scientists agree that we must not exceed more than a 2°C rise in average global temperatures, if we want to avoid catastrophic impacts from climate change. Some of these impacts include the shrinking of glaciers, loss of sea ice, a rise in sea levels, more intense and longer-lasting heat waves as well as more frequent extreme weather events such as hurricanes and tornados. Rising temperatures can lead to more high-temperature days, which can put people at greater risk for heat-related illnesses and dehydration. More frequent extreme weather events also means potentially more deaths and injuries caused by storms and floods and their aftermath (e.g., outbreak of diseases). Changing climate patterns can also lead to changing distribution of insects which carry potentially fatal diseases.

The Kyoto Protocol, an international agreement by the United Nations (UN) on climate change, identifies six main greenhouse gases. They are carbon dioxide (CO2), methane (CH4),nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6). Water vapour, although not on the UN list, is also a greenhouse gas. Not all of these gases are equally good at trapping heat. For example, methane is 25 times better at trapping heat than carbon dioxide. We call this its Global Warming Potential (GWP). One tonne of CH4 captures as much heat as (or is equivalent to) 25 tonnes of CO2. To make comparing gases easier, we convert them all into CO2 equivalents (CO2e).

Carbon dioxide
GWP = 1

Burning fossil fuels is the main source of CO2. The combustion of gasoline and diesel fuel in vehicles, coal and natural gas in electricity-generating power plants, and various industrial processes are common examples of human activities that produce CO2. Plants remove, or sequester, CO2 from the atmosphere during photosynthesis.

GWP = 25

One of the most important sources of methane is the production and transportation of natural gas, oil and coal. Domestic livestock's digestive processes and manure release methane, as do landfills when waste decomposes.

Nitrous oxide
GWP = 298

Fuel combustion in motor vehicles is the primary source of N2O. Agricultural activities, such as adding nitrogen from synthetic fertilizers to soil, also contribute nitrous oxide to the atmosphere.

GWP = 124, 22, 800

Though these GHGs do not have very high concentrations in the atmosphere, their incredibly high GWPs mean that they can have an important warming effect. All three types of gases are synthetic, meaning that do not occur naturally in the environment. They are produced as a result of a variety of industrial processes, including transmitting electricity and air conditioning systems.

Figure 1: Canada’s Total Greenhouse Gas Emissions (2012). Source: Environment Canada.


Sylvie Trottier

I'm a greenhouse gas analyst at a company called Ecometrica, where I help companies measure their greenhouse gas footprints. I’ve worked in the sustainability field in one form or another since finishing university (first getting a bachelors in environmental science and then a masters in environmental policy). It’s something I’m really passionate about, and it’s giving me the chance to work with great non-governmental organizations, like the David Suzuki Foundation, to do community outreach as a sustainability officer with a non-profit housing group, and to help coordinate projects with an electric utility research center.

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