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Air is a mixture of different molecules. Its composition is the result of chemical reactions, atmospheric motion, and emissions from a variety of sources, both natural and manmade. One of these emissions is carbon dioxide (CO2). CO2 is a greenhouse gas: it traps the heat from sunlight close to Earth's surface. In their natural balance, greenhouse gases make Earth habitable for humans and other living things. However, a change in their concentration may affect atmospheric temperatures dramatically. In fact, most climate scientists are convinced that an increased concentration of CO2 in the atmosphere is one of the leading drivers of global warming today.
In this lesson, students will discover how carbon dioxide is added into the atmosphere and the effect it's having on environmental public health. The lesson begins with a brief review of the molecules that make up air. Students use LEGO bricks to model these molecules, with individual bricks representing the atoms that make up the molecules. Continuing with LEGO bricks, they investigate how CO2 enters the atmosphere through a chemical reaction called combustion. Next, students learn about the relationship between air and atmospheric conditions, and watch a video that describes environmental disasters associated with atmospheric warming. They learn how the concentration of CO2 in the atmosphere correlates with temperature and then explore an interactive activity that details the potential impact of atmospheric warming on human health. The lesson ends with a class discussion of ways to reduce the concentration of CO2 in the air.
Note: This lesson may be followed up with the Understanding Air: Air Pollution and Modeling Pollutants with LEGO® Bricks Lesson Plan, which demonstrates other forms of pollution that result from incomplete combustion and other chemical reactions in the air.
Climate Change and Human Health Interactive
Printing instructions: Set scaling to "0%" or "none" so that the LEGO bricks on the printouts are actual size. Print two-page documents back-to-back and laminate, if possible; or print one-sided and use a plastic sleeve.
1. Explain that air is a mixture of gases and is essential to life. Even though air is invisible, it is all around us. Air is made up of molecules (groups of two or more atoms that are bonded together). The types and amounts of atoms and molecules in air can impact both environmental and public health.
2. To pique student interest, and to uncover any misconceptions students may have about air, conduct a class survey. Hand out the What Is Air Made Of? Guess! Document survey, have students look at it, and then have them vote anonymously by raising their hands with their heads down and eyes closed. Before revealing the correct answer (B), tally their votes and put them up on the board.
Note: The answer to the survey question is printed on the back of the handout, so tell students not to turn it over.
If time allows, have students debate the question, then vote to see whose answer was most convincing. Or, ask students to discuss what they know about air that might help them answer the question. You may reveal the correct answer to the class or allow them to discover it for themselves in the next step.
3. Tell students they will now have a chance to make a model of air. Distribute one LEGO® Atoms and Molecules Layout Mat Document to each group of two or three students. This document explains the contents of the LEGO brick set. You may also distribute the LEGO® Atoms and Molecules: Chemical Reactions Student Worksheet Document to refresh the students' understanding of the types of matter.
Explain that they will use the LEGO bricks to model tiny particles of matter that are too small to be seen. Each brick represents an atom, and they will use these atoms to build four types of molecules: nitrogen, oxygen, carbon dioxide, and water. Using the back of the What Is Air Made Of? Guess! Document as their guide, have them construct a model of air that reflects the correct components and their concentrations.
After they have done this, point out the "390 parts per million (ppm)" label under the CO2 molecule. Have students convert 20 percent oxygen and 80 percent nitrogen into ppm. (That is, convert the fractions 20/100 = x/1,000,000 and 80/100 = x/1,000,000.) The answers are 200,000 ppm for oxygen and 800,000 ppm for nitrogen. Compare the figures for oxygen and nitrogen with that of CO2.
Finally, ask students if they know what the number "350" stands for in the context of CO2 and climate change. (It is the ppm number that climate scientists have determined is the safe upper limit for CO2 in our atmosphere. This suggests that the current concentration is unsafe.)
4. Explain to students that the burning of fossil fuels is the largest humanmade source of carbon dioxide, and that driving cars is one of the primary activities during which fossil fuels are burned. Tell the class that they are now going to use their LEGO sets for an inquiry activity to discover how CO2 is produced in an automobile engine.
First, ask students, What makes conventional car engines run? (Newer electric and hybrid cars should be omitted from the discussion.) In other words, What three things go into the engine? Student answers should include gas, air, and a spark. If they don't mention a spark, you might give them a hint by telling them spark plugs are positioned inside the engine chamber, to provide one of the three things the engine needs to run.
Next, ask, What comes out of the engine when it is running? Their answers should include heat, exhaust gases, water, and black particles or soot. If they need prompting, ask them what the hood of a car feels like after a long drive, or if they've ever seen smoke coming out of a car or something dripping from the tailpipe.
Finally, ask students to summarize what they've learned: "A car engine runs because it burns fuel." Or "Fuel + air + a spark (to start) makes for combustion." Be sure to mention the name of the reaction—combustion—and give a general description of it. For example, "When fuels burn, combustion is taking place." Or, "If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas."
5. Students will now model how CO2 is produced during combustion.
First, explain to students that fuels, such as the gasoline used in cars, are mixtures of different molecular compounds called hydrocarbons. Hydrocarbons contain only hydrogen and carbon atoms.
Next, have students build oxygen and hydrocarbon molecules using the LEGO bricks and the Burning Fuel: Complete Combustion Document as a guide. Wait until all students have built the LEGO molecules and placed them on the pictures on Side 1 of the handout. Instruct students to return all the other bricks to the kit.
Note: The handout will provide shapes for C3H8 (propane), O2, H2O, and CO2 and instructions for modeling the chemical reaction.
Explain that propane is another type of fuel. Students might recognize the name because it is commonly used for outdoor grills. You might mention that octane, which is found in gasoline, is similar to propane but has eight carbon atoms instead of three. For this lesson, propane is easier to model.
Next, write the following chemical reaction on the board:
Mention the "Spark!" Then have students turn the Burning Fuel: Complete Combustion Document over to Side 2 and build the products using the same LEGO-brick atoms from the reactants. Students should recognize that water and carbon dioxide (shown in panels 1 and 2) are the products of complete combustion. Panel 3 introduces the fact that a CO2 molecule has the ability to trap heat, preventing its escape into space. You may want to reiterate to your students that, in reality, CO2 molecules are much too small to be seen.
Note: Before moving to Part III, have students put away the LEGO bricks and close the lid to avoid possible distractions.
6. Briefly discuss with the class that the composition of air can affect the temperature in Earth's atmosphere. Emphasize that what's contained in the "less than 1 percent" has the most influence. Then show students the Global Warming and the Greenhouse Effect Video. It describes some of the types of environmental disasters caused by atmospheric warming and suggests that "pollution" caused by humans is to blame for the rise in global temperature. Watch the first 1:10 of the video, until the narrator says "…to power our energy-intensive world."
After showing the video, you might mention that in December 2009, EPA announced for the first time that greenhouse gases, including CO2, contribute to air pollution that may endanger public health.
7. Lead a brief discussion about CO2. Even though it makes up such a small part of air, it is a potent greenhouse gas. Most scientists agree that the recent increase in global temperature results at least in part from human activities. Data used to support this conclusion show a rise in the concentrations of certain greenhouse gases that correlate with rising global temperatures.
8. To reinforce this idea with respect to CO2, have students review the chart in the CO2 Concentrations at Mauna Loa Observatory Hawaiʻi Document. This chart illustrates CO2's rise over time in the atmosphere, from 1958 through 2003. Overall, CO2 levels have risen from fairly stable levels before the Industrial Revolution (280 parts per million), to much higher levels today (392 parts per million as of 2011).
Before moving on, ask the class why they think average CO2 levels increased each year as represented in the graph.
9. Next, tell the class they're going to review the physics of the greenhouse effect and explore how CO2 gets into the atmosphere. Show students the Global Warming: The Physics of the Greenhouse Effect Video.
After watching the video, ask students to do the following:
10. In the proper balance, greenhouse gases make life on Earth possible. However, any increase in the concentration of these gases can alter the natural balance and dramatically change global temperatures. When CO2 and other heat-trapping emissions are released into the air, they act like a blanket, holding heat in our atmosphere and warming the planet.
Lead a brief discussion of the blanket analogy. Ensure that students understand that an increased concentration of CO2 molecules in the atmosphere means that there are more molecules present to absorb and "trap" the energy from the Sun, which will cause the temperature of the atmosphere to increase.
Show students the Climate Change and Human Health Interactive. It explores how unchecked CO2 emissions may affect human health. Specifically, it examines the link between atmospheric warming and increased incidence of disease. It also describes the potential consequences of exposures and outbreaks and suggests some ways communities, governments, and public health workers can act to reduce the impact.
11. Around the world, people are growing increasingly concerned about CO2 emissions. While there are skeptics who argue that global warming is a natural phenomenon, the idea that humans are contributing to it is much more widely accepted. Ask students to think of some things individuals, scientists, and governments can do to reduce CO2 emissions and help slow climate change. Students' ideas might include the following:
Optional: You may want to direct advanced students to review the Carbon Cycle Diagram Image to learn more about human activities and other sources that release CO2 into the atmosphere, and the Capturing Carbon: Where Do We Put It? Interactive to learn about some of the places we might store CO2 and prevent its release into the atmosphere. These resources may also provide helpful background information for teachers.
Each group of two or three students should be able to model (with LEGOs) the production of CO2 from burning hydrocarbons, summarize the physics of the greenhouse effect, and describe some potential effects of atmospheric warming on human health.
You might also have students extend their thinking on this subject by asking, What other activities besides driving cars do millions of people do that emit tons of carbon dioxide into the atmosphere?
Answers might include breathing, heating our homes by burning wood or coal, cutting down trees, flying on jets, and manufacturing cement—which by itself accounts for 5 to 10 percent of the world's CO2 emissions.