What's in the Air We Breathe?
Learning Objectives
Students will be able to:
- Identify the major gases that make up Earth's atmosphere
- Create an accurate pie chart showing air composition
- Explain why knowing air composition matters for health
- Distinguish between "clean air" and "polluted air"
The Big Question
"Take a breath. What did you just inhale?"
Composition of Air
Most people are surprised to learn what air is actually made of!
| Gas | Formula | Percentage | Notes |
|---|---|---|---|
| Nitrogen | N2 | 78% | Most abundant - we don't use it when breathing |
| Oxygen | O2 | 21% | Essential for respiration |
| Argon | Ar | ~1% | Noble gas - completely inert |
| Carbon Dioxide | CO2 | 0.04% | ~420 ppm - increasing due to fossil fuels |
| Other trace gases | Various | <0.01% | Neon, helium, methane, etc. |
Common Misconceptions
Misconception
"Air is mostly oxygen"
Reality
Air is 78% nitrogen, only 21% oxygen
Misconception
"CO2 is the second most common gas"
Reality
Argon (0.93%) is more common than CO2 (0.04%)
Activity: Create a Pie Chart
- Predict First: Draw a pie chart showing what YOU THINK air is made of
- Learn the Facts: Review the actual composition data
- Create Accurate Chart: Draw an accurate pie chart using the real percentages
- Nitrogen: 78 parts (78%)
- Oxygen: 21 parts (21%)
- Argon: 1 part (~1%)
- CO2 and other: less than 1 part combined!
- Compare: How different was your prediction from reality?
Why This Matters
Nitrogen (78%)
We don't use it directly - it goes in and comes back out unchanged
Oxygen (21%)
Below 19.5%: breathing becomes labored. Above 23.5%: fire hazard increases
CO2 (0.04%)
We exhale ~4% CO2 (100x atmospheric level). Builds up indoors!
Key Takeaway
If CO2 is only 0.04% of air, why does it matter so much for indoor air quality and climate? Small concentrations can have big effects - like how a tiny amount of food coloring changes water color. Next lesson, we'll learn about "parts per million" to understand these small but important amounts.