In this optional activity, students learn about the concept of parts-per-million (ppm) in order to understand how small amounts of pollution can have a large effect on the environment. They  do this by returning to their Pollution in a Jar activity and using mathematical reasoning skills.

Approximate Time: 30-45 minutes

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Objectives:

• Students will develop an intuitive and mathematical sense of the unit parts-per-million

• Students will understand that very small amounts of pollution can have a big effect on the atmosphere

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Materials:

• Atmosphere in a Jar (from previous activity)

Handouts:

• How Much is a PPM?

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DCI: ESS3.C – Human Impacts on Earth Systems

SEP: Using Mathematics & Computational Thinking

CCC: Scale, Proportion, and Quantity

How long would it take you to count to a million?

• Some students may try to calculate, others may guess. Both methods are fine because the goal of this lesson is to help students develop both a mathematical and an intuitive sense of large numbers.

• After students have reached their answers, go over how to find out the answer (assuming one counted number per second):

• See how this compares with students’ estimates/calculations. Use this to start reinforcing for students how large 1 million is.

Show students the graph from Activity 4 (below) that shows the amount of carbon dioxide levels in the atmosphere:

Point out that the scale for carbon dioxide on the right side is in parts-per-million. 

Ask them if they’ve ever seen this unit before. It is unlikely – this is a pretty unusual unit! Tell students that today they’re going to think about how much carbon dioxide is too much, and how low it needs to be to slow down or stop the global temperature from rising.

Take out the atmosphere in a jar from the previous activity, and remind students of what it represents. Hold up one bean of carbon dioxide (whatever bean you chose to represent it), and remind students that this bean represents carbon dioxide. Return to the graph of carbon dioxide levels and point out to students that the current level of carbon dioxide in the atmosphere is about 414 parts per million (for current levels visit https://www.co2.earth/). That would mean that there would be 414 beans in a jar that had a million beans in it. Ask students how many beans that would be in their jar that has far fewer beans. Have students record their guesses for later.

Hand out the “How Much is a PPM?” sheet to students, and have them read the first section. Use a reading strategy to help students focus on key points and questions they have about of the reading. When students are done, have them share key points, and use peer discussion to help answer any questions they have.

Show students the animated video “How to Visualize One Part Per Million" below:

Take out the atmosphere jar and remind students of their guesses from earlier in class about how many “beans” of carbon dioxide would need to go into their jar to make it equal to 414 parts per million. See if the students want to revise their estimates based on the reading.

Read the next section of the handout together (“How much carbon dioxide is in our jar?”). Have students write the fraction for the amount of carbon dioxide in the atmosphere on their papers in the box.

Note: You will need to adjust the fractions in the next section if you used a different amount of beans than the suggested amount.

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Next, ask students how they could figure out what the fraction would be if they put one bean of carbon dioxide in their jar. Ask students to write the fraction representing the ratio of pollution to air in the jar in the box on their paper next to the carbon dioxide amount like this:

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Have students turn to a partner to determine which fraction is larger. If they get stuck on this, suggest that they multiply the second fraction by 414/414 to make equivalent numerators.

After a few moments, have them share their findings. When they agree that the “jar” fraction is smaller (414 out of 2,070,000 is less than 414 out of 1 million), have them write an inequality symbol between the fractions to show this.

With their partners, have students determine what this means. Does one bean of carbon dioxide in the jar mean it is more or less than the amount in the atmosphere? Bring the class back together, and let them discuss until they agree that one bean in the jar is not enough because it is still less than the amount in the atmosphere.

Tell students that they know they need more than one bean, but how many do they need? To figure it out they need to make equivalent fractions. Write this on the board and have them add it to their papers (if they are familiar with variables, you can use “x” instead of the “?”

Ask how they can figure out what goes in the space with the question mark. There are many different ways to solve this (ex. cross multiply and divide). To continue with finding equivalent fractions, you can suggest that they can divide the top and bottom by the same number to get an equivalent fraction. What number do you need to divide 1,000,000 by to get 5,000? They can solve this with guess-and-check, or by dividing. Give partners time to figure out what the answer is. When they figure it out that it is 200, ask them what the numerator in the equivalent fraction should be (2.07). Have them write 2.07 into the space where the question mark is.

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Ask students how many carbon dioxide beans this means they should put into their jar (2). Ga back to students’ guesses from earlier in the class to see if anyone was right (or close).

Ask students if they are surprised that such a small amount of carbon dioxide can have such a big effect on the environment. Take a moment to have students consider this effect. You may want to have them make an analogy to their own lives or to their experience (has one day in their life been very important? Can one person make a difference in the lives of millions of others?)

Tell students that the carbon dioxide level in the atmosphere 100 years ago was 303 ppm. Have them write this as a fraction, and see if they can figure out how many beans (or parts of beans) they would need in their jar if it was 100 years ago.

There would be about 1.5 beans of carbon dioxide in the jar 100 years ago.