The EPA has identified six common air pollutants: ozone, particulate matter, carbon monoxide, nitrogen dioxide, sulfur dioxide and lead. Automobiles and other modes of transport (buses, trucks, etc.) play a large role in the emissions of many of these types of dangerous pollution, emitting four of the six common pollutants into the environment. While environmental policies have helped to greatly reduce the amount of emissions per vehicle, the number of vehicles on the road, and the distance traveled per vehicle, have both greatly increased.

Ozone is made up of three molecules of oxygen, and its chemical formula is O3. Ozone can be "good" or "bad" depending on its location. "Good" ozone is located high in the atmosphere and protects the earth from damaging UV rays from the sun. This beneficial ozone layer is slowly being destroyed by man-made chemicals. A good example of this is found in the "ozone-hole" over the North and South Poles. "Bad" ozone is found lower in the Earth's atmosphere. It is created (see the equation below) when emissions from cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. "Bad" ozone contributes to both environmental and human health problems.

As illustrated in Figure 1, motor vehicles have an enormous impact on the formation of ozone by emitting Nitrogen Oxides (NOx) and Volatile Organic Compounds (VOCs).

Figure 1. Sources of NOx and VOCs. click for copyright

Particulate matter is what you see when there is haze or smog in the air. Particulate matter can either be directly emitted from vehicles, factories, farming activities and fires, or it can be the indirect result of burning fuels in the presence of sunlight and water vapor, such as fuel combustion in vehicles and power plants (see Figure 2). Particulate matter plays a huge role in health problems and also impacts the delicate chemical balance of eco-systems. Particulate matter is also responsible for the oftentimes permanent staining of statues and buildings.

Figure 2. Particulate matter is both directly and indirectly emitted into the environment. click for copyright

Carbon monoxide (CO) is a gas that is released when fuel is not burned completely. Carbon monoxide is very dangerous to human health, and, ironically, more than one half of the CO emissions come from on-road vehicles. Other sources include non-road vehicles, such as trains and airplanes, industrial processes, fuel combustion and miscellaneous sources, such as forest fires. The breakdown of percentages of CO contribution to our environment is shown in Figure 3. Carbon monoxide, an organic compound, also contributes to the formation of ground level smog or ozone.

Figure 3. On-road vehicles account for more than half the carbon monoxide (CO) emissions. click for copyright

Nitrogen Oxides (NOx) refers to a group of gasses that contain nitrogen and oxygen. They are one of the primary components of ozone, and the main source is, again, motor vehicles. NOx contributes to the formation of acid rain and deteriorates water quality. NOx emissions also contribute to atmospheric particles which cause respiratory problems and visibility impairment.

Figure 4. Motor vehicles account for more than half the Nitrogen Oxide (NOx) emissions. click for copyright

Sulfur dioxide (SO₂) comes mainly from burning coal in large industrial processes, but also from trains and boats with coal-burning engines. Sulfur dioxide contributes to respiratory illness, acid rain and visibility impairment. Motor vehicles contribute 5% of sulfur dioxide emissions. The majority of lead pollution now comes from metal processing. However, in the 1970s, motor vehicles were responsible for almost 80% of lead pollution. Environmental laws leading to the removal of lead from gasoline have essentially eliminated on-road vehicle lead pollution.

As seen recently in the news media, alternative fuels and vehicles have been developed and are gaining mainstream popularity.

The main two types of alternative vehicles are hybrid and electric. The common hybrid vehicle is a gas-electric hybrid, utilizing both gas and electric engines to increase fuel efficiency and greatly decrease emissions. Electric vehicles rely solely on electric battery power to run the vehicle, which causes them to have no need for gasoline and very low emissions. Each vehicle has its limitations, though both show a movement towards decreasing vehicle emissions and taking responsibility for protecting our environment.

Biodiesel is an animal fat- or vegetable oil-based alternative fuel which has much lower emissions than regular unleaded or diesel fuels. Biodiesel is a sustainable and non-toxic resource that can be made locally and from recycled ingredients, such as vegetable (soybean) oil used at restaurants. These ingredients are processed at a refinery and turned into a fuel-grade product. Remember, you cannot just put vegetable oil into your vehicle's gas tank and expect it to run - that would definitely harm your car's engine.

Other possibilities for alternative vehicles in the future include increasing the efficiency of hybrids and ease of use of electrics as well as the development of hydrogen-powered cars. Hydrogen cars are close to zero emissions and use an infinitely renewable resource.

There are several methods of producing energy that have less impact on the environment. Each method has its pros and cons. Some examples are:

Wind Turbines - Clean energy using wind power; limited by the amount of wind available. Solar Power - Clean energy using the sun; limited by weather (i.e., the number of sunny days or hours available); photovoltaic cells are still quite expensive.

Biodiesel - Fewer harmful emissions than regular gasoline or diesel; must have a diesel engine to use biodiesel, and gas stations selling biodiesel are still sparse in some states.

Nuclear Power - While a fairly clean source of energy, it is very controversial as there are huge health risks associated with it should an accident or contamination occur with its use.

Hydroelectric Power - Energy from flowing or falling water; though a cleaner and renewable form of energy, there are controversial issues involved dealing with changing a natural water course and the impact on the ecosystem.

Discussion Questions: Solicit, integrate and summarize student responses. Have the students form small groups and talk about different types of transport.

• What engineers do they think are involved in each type of transportation?
• How does each type of transport contribute to air pollution?
• Ask the students if they can think of means of transport that do not contribute to air pollution.
• Ask them why air pollution is a bad thing. (Answer: Because it makes people sick, hurts animals, and harms plants, trees, buildings, etc.)

Transportation Rating System: Ask the students to brainstorm a list of different methods of transportation. Have the students break up into groups and have each group rank the list in order from cleanest to not-as-clean. Have the students make a list of features that they will judge each mode of transport on, such as "greenness," efficiency, ease of use, etc. Rate each type of vehicle and total the numbers to find out which one is the best. Have each group quickly present the order that they decided, and as a class come to a consensus about which travel modes are the best for the environment.

Example:

My Life as an Environmental Engineer: Ask if any student can call out the four renewable energy sources that they learned about (wind, water, solar, biodiesel). Have students pretend to be environmental engineers and ask them to think of something they could design to help keep the water or air clean. Next, ask them to think how their invention could use a renewable energy source. For example: an air filter that is powered by biodiesel, or a water filter that uses solar energy to run the pump.