Explore the origin and environmental impact of pollutants in car exhaust emissions using peer-assessed writing in this lesson plan for 16–18 year olds

In this activity, students write a short piece on the origin and environmental implications of pollutants in car exhaust gases. They agree their own criteria for judging the writing which they then use to evaluate the work of a fellow student.

This sequence could be used instead of a formal teaching of this topic.

Learning objectives

Students will be able to:

  • Explain the origin and the environmental implications of pollutants in car exhaust gases.

Sequence of activities


  1. Show an appropriate photograph (archive or digital), or a short video filmed in the local community, showing car exhausts or cyclists wearing smog masks.
  2. Share the session objectives with students.

Activity, stage 1: identifying pollutants

  1. Give a mini whiteboard to each student and ask them to write down the names or formula of pollutants from car exhausts.
  2. Pose questions to individual students to ensure that the following pollutants are identified:
    1. Unburnt hydrocarbons.
    2. Carbon monoxide.
    3. Carbon dioxide.
    4. Nitrogen oxides.
    5. Sulfur dioxide.
  3. Advise the students:
    • That they are going to write an account of the origin and implications of pollutants in car exhausts.
    • On where they can find the necessary information.

Activity, stage 2: suggesting criteria

  1. Arrange the students in pairs.
  2. Ask each pair to draw up a series of criteria which could be used to judge whether a student account had effectively covered the topic. They might include criteria such as:
    • All five pollutants are covered.
    • The origin of all pollutants are explained.
    • Equations are included where appropriate.
    • The environmental effects of all five pollutants are explained.
    • Correct chemistry.
    • The account contains sufficient detail.
    • The account is clear.

Activity, stage 3: agreeing criteria

  1. Bring all the students together and obtain suggestions for criteria from different pairs.
  2. Agree a shared list of criteria with the whole group.

Setting the writing as homework

Set homework for the students to write up their account by a specified future date, and:

  • Explain that their account will be evaluated by a fellow student using the agreed criteria so they should leave space down one side of the page for their comments.
  • Suggest that the students think about including diagrams and equations.
  • If facilities are available, ask for the reports to be word processed.

Activity, stage 4: peer assessment

At a subsequent session, arrange for students to exchange their account with another student. Before they start to evaluate the work of the other student remind them to:

  • Use the agreed class criteria.
  • Write comments on the work indicating where the criteria have been met.
  • Indicate where criteria have not been fully met.

Provide time:

  • For students to comment on and share with other students what they found easy and what they found difficult in researching and writing about this topic.
  • For students to look at the comments made by their student assessor.
  • For additions to be made to the report, in response to these comments (in or out of class).


Take in the work. Write comments which reinforce the good features. Identify any points that still need developing and where the student can find additional support.


Showing a striking image to illustrate pollution from car exhaust gases allows the session objectives to be shared with students in a vivid fashion.

Through the process of agreeing the criteria against which their account will be judged, students are helped to recognise the standards that they are aiming for. Knowing these criteria and knowing that a fellow student will be doing this judging are stimuli for the research and the writing. Students also evaluate their performance as they identify what they found easy and what they found difficult.

Final comments by the teacher, on the student written accounts, will validate the peer assessment.


For each student:

  • Mini whiteboard
  • Access to information about pollutants in car exhausts.

For the electronic image:

  • Electronic image showing pollution from car exhaust gases
  • Data projector


Points about pollutants that might be included

Unburnt hydrocarbons

  • Origin: unburnt fuel.
  • Environmental implications: contributes to photochemical smog.

Carbon monoxide

  • Origin: incomplete combustion of hydrocarbons in petrol.
  • Environmental implications: greenhouse effect, toxic to humans.

Carbon dioxide

  • Origin: from combustion of hydrocarbons in petrol.
  • Environmental implications: greenhouse effect.

Nitrogen oxides

  • Origin: combustion of nitrogen and oxygen in air when spark is passed in car engine.
  • Environmental implications: acid rain, damage to ozone layer, toxic to humans, contributes to photochemical smog.

Sulfur oxides

  • Origin: combustion of sulfur or sulfur compounds in petrol.
  • Environmental implications: acid rain, toxic to humans.

Equations that might be included

  • CxHy + (x + y/4) O2 → xCO2 + (y/2) H2O
  • CxHy + (2x + y/4) O2 → xCO + (y/2) H2O
  • N2 + O2 → 2NO
  • 2NO + O2 → 2NO2
  • S + O2 → SO2
  • 2SO2 + O2 → 2SO3