Unit 3.2 Why are there layers of the atmosphere?

By the end of this unit, students will be able to:

• Explain the relationship between pressure and volume
• Predict how air pressure should change with altitude
• Define density
• Explain how pressure, volume, and temperature vary within the layers of the atmosphere
• Explain the relationship between pressure and temperature
• Use the law of conservation of energy to diagnose how pressure, volume, and temperature variations result in clouds in the atmosphere. (extension activity)

This unit introduces the concept of density using the atmosphere as a real-world application. Continuing on with observing the unobservable, students will examine and interpret properties of the atmosphere and how those properties contribute to the structure of the atmosphere. The second activity (Graphing the Atmosphere) is the main data-driven exercise for students to apply the concepts of pressure, temperature, and density to build their understanding of the stratified nature of the atmosphere.

These materials build a foundation for understanding the unit's motivating question, but also function well as a standalone module. Plan for these materials to take about 160 minutes of class time, plus an additional 20 minutes if the extension cloud in a bottle activity/demonstration is also completed. These materials were developed for use in an in-person synchronous classroom and are suitable for any size of classroom.

Teaching Materials:

All Slides: U3.2 All Slides New.pptx (PowerPoint 2007 (.pptx) 8.9MB Jul10 24)

Materials:

• Boyle's Law (one set-up for every 1-2 people in the class): syringes (or popper toys), tubing (optional).
• Trash bag "air ship" (demo - only one setup needed): shop vac and 80+ gallon trash bags.
• Crush a can with atmospheric pressure (demo - only one setup needed): empty soda can w/ a few tbsp water inside, tongs, single burner, ice water.
• Cloud in a bottle activity (demo - only one setup needed): 2L plastic bottle (or glass), lid with small hole drilled or rubber stopper, water, matches, bike or hand pump, instructor notes file U3.2 Cloud in a Bottle Instructor notes.docx (Microsoft Word 2007 (.docx) 4.2MB Jul10 24)

Videos: WeatherBalloonLaunch.MOV (Quicktime Video 20.6MB Jul10 24), PopperToy.mov (Quicktime Video 3.3MB Jul10 24), PopperToy2.mov (Quicktime Video 5.2MB Jul10 24), Cloud Bottle Demonstration Video.mov (Quicktime Video 26.5MB Jul10 24)

Graphing the Atmosphere Activity materials:

• Activity Dataset for Montana: Student worksheet: U3.2 Montana Graphing Student.docx (Microsoft Word 2007 (.docx) 642kB Jul10 24), Instructor Copy:
  U3.2 Montana Graphing Answers.pdf -- educator-only file
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• Activity Dataset for Albany, NY: Student Worksheet: U3.2 Albany Graphing Student.docx (Microsoft Word 2007 (.docx) 558kB Jul10 24), Sounding Data: Sounding Data Albany NY.xlsx (Excel 2007 (.xlsx) 11kB Jul10 24), Instructor Copy:
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• PhET hot air balloon simulation

Scientist Spotlight Full Resource (In this unit: Jason Priestley): Scientist Spotlight Slides (PowerPoint 2007 (.pptx) 4.6MB Jul8 24)

Reflection Assignment: U3.2 Reflection.docx (Microsoft Word 2007 (.docx) 68kB Jul10 24)

Sample Student Reflections (this is Reflection 8): Reflection Examples Redacted.pdf (Acrobat (PDF) 1.8MB Jul8 24)

Pre-Class Assignment(s):

Before Part I:

• Read about phlogiston and complete Scientist Spotlight Priestley
  • Be prepared to share something surprising or interesting that you learned about Priestley.

Before Part 2:

• Read properties of gases (visionlearning)
• What does it mean that pressure and volume are "proportional"? (Refer back to previous unit experience with proportionalities)

In Class, Part I (60 min)

Introduction (20 min):

• Begin by discussing the homework readings: How was the idea of phlogiston logical? Before Priestly, Lavoisier, and oxygen, how was the composition of air reasoned?
• Next, discuss the composition of the atmosphere as we know it today. How do we know its composition? (spectroscopy) How can "we" (in this classroom, today) follow the logic of phlogiston and know that air must be made of "something"?
  • We need observable evidence! Cue activity 1.

Lab exercises - investigating air pressure (40 min)

• This activity is investigating density with air pressure syringe experiments. Students use syringes as tools with which to "capture" air and experiment with it. Their mission is to find observable evidence that air is made of something.
• Think-Pair-Share or Small Groups follow their initial investigative mission, and students are to discuss: What is air pressure? What causes it? What is "dense air"? Students should then use their answers to predict how air pressure should change with increasing altitude.
• The discussion is next taken to the whole class level and connected with the observed evidence from the syringes. We consider what happened to volume and pressure as the syringe plunger was depressed. We were able to observe the relationship between pressure and volume! Students are then tasked with drawing a schematic graph representing this relationship. (Refer back to previous unit experience with graphing relationships)
• Optional additional extension activities:
  • Allow students to experience a "hug" from the atmosphere - a physical representation of the air pressure around us all the time, but that we do not feel. This activity involves the lower portion of a student being inside a large trash bag and using a vacuum to suck the air out of the bag so that the bag effectively squeezes the student's body in.
  • Crush a can using atmospheric pressure

In Class, Part II (80 min)

In class (10 min): Investigating the atmosphere: composition, pressure, and temperature

• Following the previous activity and the homework reading, begin by having the students draw a schematic graph to illustrate this proportional pressure-temperature relationship. Next, students are asked to compare this new graph with the one they drew earlier for pressure and volume.
• Task for small groups:
  • Given what you know about the atmosphere and air, predict how you expect temperature to change with altitude in the atmosphere based on these proportionalities
• These predictions lead into the next activity.

Lab exercise (60 min): Graphing atmospheric temperature and pressure data

• This activity is graphing atmospheric temperature and pressure data. Students will work in pairs or small groups to test their predictions made earlier in class.
• Atmospheric radiosonde data collected from near Great Falls, MT in July 2021 and Albany, NY in March 2023 (pick one of these or download your own from the website linked in the notes of the powerpoint slides) are provided for the students. Each group will be assigned a subset of data to graph. These graphs will be first used to test their earlier predictions, then they will extrapolate trends from their subset of data to use to make predictions about the properties of the other parts of the atmosphere that they did not graph.
• The groups are asked to discuss how their predictions compare with real values, what interpretations they can make, and then tasked with using their graphs and data to determine the location of the boundary between the troposphere and the stratosphere.
• Following this, there is an optional additional activity using a PhET simulation to explore the properties of the upper layers of the atmosphere.

In class (10 min): Connecting pressure and temperature to weather/clouds

• Weather forecasts often mention "low pressure systems" or "high pressure systems"
• Think-Pair-Share: What do these terms mean? Describe the physical process(es) that should result in forming a low or high pressure system.
• Following this and showing a weather map, students are asked to compare the weather at the high and low pressure areas.
• Next, introduce the concept of the "dew point" and discuss what causes clouds to form. Ask the students where (high or low pressure systems) they would expect clouds to form. This is a lead in to the next activity, and allows us to finally answer the question of why temperature decreases with height in the troposphere (we have observed it, but not yet explained it).

In Class, Part III (20 min)

Extension lab exercise or demo (20 min):

• This activity models how clouds form as a result of pressure changes causing condensation of water vapor into a fog or cloud
• Begin with a think-pair-share
  • What causes a gas (water vapor) to condense into a liquid?
  • Based on the data you have been examining so far in this unit (pressure, temperature, density, volume) write a hypothesis to explain the formation of clouds
• Discuss cloud "needs": 1) water to evaporate and form water vapor in the atmosphere, 2) water vapor to cool and condense. Ask students to recall the relationship between pressure and temperature that they determined earlier in the unit.
• Set up the cloud in a bottle demo or experiments in small groups
  • Have the students make a prediction about what will happen to the water in the bottle as the bottle gets pumped up with air
  • Then students should observe what happens when the lid/stopper is removed from the bottle
  • Finally, explain and discuss what happened to the gas molecules inside the bottle when the lid/stopper was removed
• Recap the explanation of why the cloud formed: As the air escaped it rapidly expanded. This can be related to our previous unit on energy: when the stopper was removed, all the energy that was once contained in the bottle is spread out over a much larger volume, so it cools.

I use a dinosaur popper toy (and a cat popper toy) to demonstrate the inverse relationship between pressure and volume (Boyle's law). These toys have proven to be a surprisingly effective way to make the concept memorable. For the second activity, graphing does not have to be perfect, but students should make an effort to get as close as they within reason for the scale of the graph paper provided. For the extension inversion activity, the demo represents only the troposphere layer within the atmosphere. Line the bottom of a large plastic tub with an insulating layer (e.g. a sheet of Styrofoam or layers of cardboard). Place the baking pan on top of this insulating layer and carefully pour in liquid nitrogen from the dewar.

This unit includes one of many Scientist Spotlights. The goal of these is to showcase an array of scientists in fields relevant to the topics of the day, some from long ago and others young and active today, together representing a diversity of people who have all overcome some challenge in pursuit of their scientific passion. Here are all relevant files related to the Scientist Spotlights:

Vacuuming students inside of a giant trash bag with a shop vac certainly can be risky. Always keep their head out of the bag! Once the student has stepped inside the trash bag, they should gather the top of it up around their neck & shoulders, holding the edge securely with one hand. My students have found the best experience position-wise in the "trash bag air ship" to be kneeling or sitting with knees up, leaning forward. The student's free hand will hold onto the hose from the shop vac, being sure to hold it away from the trash bag so that it can freely suck air without getting plugged up. From the kneeling and seated positions mentioned above, my students have held onto the shop vac hose with their free hand and between their legs, pointing the hose toward themselves and away from the plastic. Typically there is reluctance toward getting into the trash bag, but once one gets in it and receives their "atmospheric pressure bear hug" then usually everyone else wants a try. A final tip is that some shoes will tear holes in the bag, socked feet are usually safest.

The pre-class reading assignments (described above) are graded for completion only, not correctness. Administer using the same format throughout your course (through the LMS, turn in paper copies, guided discussion/participation in class, etc.). Consider setting the due date an hour or so before your class begins to give you time to summarize where your students sit with these concepts (this is a form of Just in Time Teaching).

The reflection assignment in this unit asks students to read and reflect on Vision Learning's The Composition of Earth's Atmosphere. Reflection Prompt: Reflect upon your understanding of the structure of the atmosphere (from the reading) after having completed the graphing exercises. How do you feel about your understanding of these data? Has your comfort level (with regard to the process of science and/or to making graphs) changed? Make specific connections in your reflection to the activities that we completed. As always, reflections ask students to put their learning in their own words and also to apply their knowledge in a new and novel situation.

Video from University of Washington Atmospheric Sciences Outreach that demonstrates density changes of gases with temperature (demonstrated by people role playing as atoms)

Virtual hot air ballooning by UCAR Center for Science Education an interactive simulation that takes a hot air balloon through the layers of the atmosphere and collects pressure and temperature data at different altitudes.

References for the Cloud in a Bottle Demonstration:

• What are clouds made of? Are they more likely to form in polluted air or in pristine air? This NASA article briefly explains why smoke is needed to form a cloud in a bottle.
• Aerosols and Clouds (Indirect Effects). This NASA article explains why smoke and pollution change the optical properties of clouds in more detail. This Aerosol indirect effect is one of the most important uncertainties in global warming forecasts. As we stop emitting fossil fuels and the associated particulate pollution, the optical properties of clouds will change in ways that are very difficult to precisely predict and this will change how much light (heat energy that causes warming) is absorbed by the Earth system vs reflected/scattered away to space.
• PhET Simulation: Gas Properties. Use this to reinforce the idea that the air cools when the air escapes the bottle because now that heat energy is spread out over a larger volume: As you open the container and the air escapes, the temperature of the air in the vessel decreases.