Tailpipe Emissions



Grade Level & Subject: 9-12, Chemistry,History, Environmental Studies 

Length: 1-2 class periods


After completing this lesson, students will be able to:

  • Identify components of tailpipe emissions
  • Understand the effect of tailpipe emissions on human health
  • Recognize problems and begin to identify solutions associated with automobile exhaust

National Standards Addressed:

This lesson addresses the following National Education Standards:[1]

As a result of activities in grades 9-12, all students should develop understanding of:

  • Personal and community health
  • Environmental quality
  • Natural and human-induced hazards
  • Science and technology in local, national, and global challenges
  • Content Standard: NS.9-12.7 HISTORY AND NATURE OF SCIENCE

As a result of activities in grades 9-12, all students should develop understanding of:

  • Science as a human endeavor
  • Nature of scientific knowledge
  • Historical perspectives

Materials Needed:

  • Reproducible #1: EPA History of Reducing Tailpipe Emissions
  • Reproducible #2: Air Pollution from Motor Vehicles in Vermont
  • Reproducible #3: South Carolina: Vehicle Maintenance and Air Quality
  • Reproducible #4: New Hampshire: Motor Vehicles and Toxic Air Pollutants

Students will be assessed through the following activities:

  • Participation in class discussion
  • Demonstrated thought and research in small group presentations



Relevant Vocabulary:

  • Emissions: Releases of pollutants into the air from a source, such as a motor vehicle or a factory.[2]
  • Hydrocarbons: Chemical compounds that contain hydrogen and carbon. Most motor vehicles and engines are powered by hydrocarbon-based fuels such as gasoline and diesel. Hydrocarbon pollution results when unburned or partially burned fuel is emitted from the engine as exhaust, and also when fuel evaporates directly into the atmosphere. Hydrocarbons include many toxic compounds that cause cancer and other adverse health effects. Hydrocarbons also react with nitrogen oxides in the presence of sunlight to form ozone. Hydrocarbons, which may take the form of gases, tiny particles, or droplets, come from a great variety of industrial and natural processes. In typical urban areas, a very significant fraction comes from cars, buses, trucks, and nonroad mobile sources such as construction vehicles and boats.[3]
  • Nitrogen Oxides:A group of highly reactive gases that contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. The common pollutant nitrogen dioxide (NO2) can often be seen combined with particles in the air as a reddish-brown layer over many urban areas. Nitrogen oxides are formed when the oxygen and nitrogen in the air react with each other during combustion. The formation of nitrogen oxides is favored by high temperatures and excess oxygen (more than is needed to burn the fuel). The primary sources of nitrogen oxides are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels.[4]
  • Ozone:A gaseous molecule that contains three oxygen atoms (O3). Ozone can exist either high in the atmosphere, where it shields the Earth against harmful ultraviolet rays from the sun, or close to the ground, where it is the main component of smog. Ground-level ozone is a product of reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight. Ozone is a potent irritant that causes lung damage and a variety of respiratory problems.[5]
  • Smog:A commonly used term for pollution caused by complex chemical reactions involving nitrogen oxides and hydrocarbons in the presence of sunlight. Ozone is a key component of smog. Smog-forming chemicals come from a wide variety of combustion sources and are also found in products such as paints and solvents. Smog can harm human health, damage the environment, and cause poor visibility. Major smog occurrences are often linked to heavy motor vehicle traffic.[6]
  • Particulate Matter:Tiny particles or liquid droplets suspended in the air that can contain a variety of chemical components. Larger particles are visible as smoke or dust and settle out relatively rapidly. The tiniest particles can be suspended in the air for long periods of time and are the most harmful to human health because they can penetrate deep into the lungs. Some particles are directly emitted into the air. They come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and wood burning. Other particles are formed in the atmosphere by chemical reactions.[7]
  • Carbon Monoxide:A colorless, odorless gas that forms when carbon in fuel is not burned completely. Carbon monoxide is a component of exhaust from motor vehicles and engines. Carbon monoxide emissions increase when conditions are poor for combustion; thus, the highest carbon monoxide levels tend to occur when the weather is very cold or at high elevations where there is less oxygen in the air to burn the fuel.[8]
  • Benzene:A cancer-causing hydrocarbon (C6H6) derived from petroleum. Benzene is a component of gasoline. Benzene emissions occur in exhaust as a byproduct of fuel combustion and also occur when gasoline evaporates.[9]
  • Carbon Dioxide: A colorless, odorless, non-poisonous gas that exists in trace quantities (less than 400 parts per million) within ambient air. Carbon dioxide is a product of fossil fuel combustion. Although carbon dioxide does not directly impair human health, it is a greenhouse gas that traps terrestrial (i.e., infrared) radiation and contributes to the potential for global warming.[10]
  • Volatile Organic Compounds:Emitted as gases from certain solids or liquids, VOCs include substances—some of which may have short- and long-term adverse health effects—such as benzene, toluene, methylene chloride, and methyl chloroform.[11]

Background Information:

Automobiles typically run on gasoline or diesel fuel, both of which are a composite of different chemicals collectively known as hydrocarbons. Mainly carbon and hydrogen, hydrocarbons are Volatile Organic Compounds (VOCs), meaning that they readily evaporate at normal temperatures. According to the Environmental Protection Agency, they are a precursor to ground-level ozone and smog. Hydrocarbons result in dangerous emissions because our vehicles do not operate in a vacuum. In a “perfect” combustion engine, all the hydrogen in the fuel would be converted to water by the oxygen in the air. Meanwhile the carbon in the fuel would be converted to carbon dioxide, and the nitrogen already in the air would remain unaltered. However, as is clearly the case, we do not operate in a vacuum, and none of our vehicles are equipped with a perfect engine. Instead, incomplete combustion, combined with high pressure and temperature, results in several toxic exhaust pollutants:

  • Carbon Monoxide
  • Nitrogen Oxides
  • Sulfur Oxides
  • Carbon Dioxide

In addition to exhaust pollutants, petroleum-based fuels also emit dangerous compounds due to evaporation. Typically, these emissions stem from storage tanks and fueling lines. As has been stated, hydrocarbons are VOCs which means that, especially on hot days, they contribute significantly to ground level ozone as they are released from vehicles (both parked and driving), gas stations, and anywhere gas or diesel is stored. A key component of smog, ground-level ozone is formed by reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight. Particulate matter as well, though not a chemical compound, is nevertheless a serious health concern as an auto emission.


  • Health Impacts of Air Pollution in Los Angeles County Powerpoint


  • LA Times: Standards will limit tailpipe emissions


  • NREL Newsroom


  • UMN Vehicular Exhaust and Air Pollution


  • Consumer Product Safety Commission: Carbon Monoxide Questions and Answers


  • EPA: Particulate Matter


  • EPA: Nitrogen Dioxide


  • EPA: Sulfur Dioxide




Warm-up: What is released from your car’s tailpipe?

  1. Write the names of the emissions listed below on the board, and ask the class if they can guess what all of them have in common. Answers may vary. Explain to them that one trait that all the words on the board share is that they are all hazardous to human health. Proceed to detail the health effects of each item.
  2. Carbon Monoxide: reduces the amount of oxygen reaching the body’s organs and tissues, aggravates heart disease.
  3. Nitrogen Oxides: aggravates lung diseases, can contribute to asthma and other respiratory problems.
  4. Sulfur Oxides: aggravates asthma
  5. Carbon Dioxide: headaches and dizziness when exposed to an abundance of the compound.
  6. Benzene: is a known carcinogen.
  7. Ozone: causes lung damage and a variety of respiratory problems.
  8. Particulate Matter: decreased lung function, asthma, development of chronic bronchitis, nonfatal heart attacks, and premature death in people with heart or lung disease.
  1. Ask the class if they can guess another commonality shared by all of the items on the board. Answers may vary. They may be surprised to learn that all of these items are released as emissions from the cars that they most likely drive in everyday. Feel free to reference the information section if you choose to explain why the emissions exist.
  2. "Perfect" Combustion:
    Fuel (hydrocarbons) + air (oxygen and nitrogen) = carbon dioxide + water + unaffected nitrogen
  3. Typical Engine Combustion:
    Fuel + air = unburned hydrocarbons + nitrogen oxides + carbon monoxide + carbon dioxide + water[12]
  4. Explain to the class that the current level of emissions per vehicle are today much lower than in the past. Ask them if they can imagine, given their new knowledge of the health effects of tailpipe emissions, how hazardous things were 40 years ago. Do they have any idea how many cars and trucks there were on the road in 1970? 108,418,197[13]. The year 2000? 221,475,173.2008? Over 250 million.[14] How dangerous would the environment be if regulation had never been adopted?Answers may vary. And what exactly are these regulations? Take the class through Reproducible #1. Feel free to split up the text, and have students read individual paragraphs. 

Activity One: Real World Ramifications

Activity one will give a couple real world examples of the problem with auto emissions, and ask students to research solutions to those problems.

  1. Now that they have an idea of how vehicle regulations came into being, have the class examine contemporary issues and research solutions. Depending upon the size of your class, break students into “solution-finding small groups.” Each group will be responsible for researching a different manner of reducing emissions. They should complete their research as homework, and be ready to present during the next class period.
  2. Break the class up into groups based on potential emission reducing strategies. These could include: hybrid cars, electric cars, ways to increase gas mileage, MTBE and other gasoline additives, ethanol, biodiesel etc. They should structure their research and strategies as if they were governing a particular state. Allow groups to choose their state, and make them aware that they should be prepared during the next class period to present the pertinent data for their respective states (i.e. how many vehicles are currently on the road, and how much driving is done – this information can typically be found on the state’s DOT website.), as well as their group’s plan to mitigate emissions.
  3. Before they dive into the research, students should become more aware of the current problem. In order to facilitate this, present Reproducibles #2 – 4 to the class either on an Overhead Projector or Smart Board. Also, consider showing the Los Angeles Powerpoint (listed first in the reference section) in order to give students an idea of some mitigating strategies.

Wrap Up: The Future

  1. During the next class period, have state groups present their findings and subsequent strategies they researched in order to mitigate harmful tailpipe emissions. Steer this into a conversation centered on what must be achieved for a cleaner future versus what is actually possible. Your students are the future leaders of this country. What limits are they willing to tolerate when it comes to clean air and human health? Where will they sacrifice for convenience? How much pushback to they think will come from the automotive industry?

Extension: Environmental Effects

  1. The toxicity of tailpipe emissions affects much more than human health. The environment, animals, bodies of water, and the Earth as a whole suffer because these compounds are emitted into the air. Encourage interested students to pursue extra inquiry into its effects.



Students have examined the history of the automobile in films as a catalyst for advertising. They now have an understanding of how the “car culture” came to be in America, and they have done their best to guess at its future. They’ also touched on the role of technology in determining driving habits.



Joshua Volinsky– Author, Editor

            Green Schools Coordinator, Earth Day Network

[2]“ Emissions Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[3]“ Hydrocarbons Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[4]“ Nitrogen Oxide.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.


[5]“ Ozone Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[6]“ Smog Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[7]“ Particulate Matter Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[8]“ Carbon Monoxide Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[9]“ Benzene Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[10]“ Carbon Dioxide Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[11]“ Volatile Organic Compounds Entry.” U.S.Environmental Protection Agency. Retrieved July 11, 2011 from http://www.epa.gov/otaq/invntory/overview/definitions.htm.

[12]“The Environmental Impact of Vehicle Emissions.”University of Connecticut – School of Engineering. Retrieved July 11, 2011 from http://www.engr.uconn.edu/~garrick/ce320/2007/Lecture%207%20-%20The%20Environmental%20Impact%20of%20Vehicle%20Emissions.doc.

[13]Highway Finance Data & Information.” U.S.Department of Transportation. Retrieved July 11, 2011 from  http://www.fhwa.dot.gov/policyinformation/pubs/pl08021/fig3_1.cfm.

[14]“Number of U.S. Air Craft, Vehicles, Vessels, and Other Conveyances.”Bureau of Transportation Statistics.http://www.bts.gov/publications/national_transportation_statistics/html/table_01_11.html.