Background:

Carbon dioxide is a colorless, odorless, incombustible gas that is a product of respiration and combustion and a natural component of the air on this planet. It is one of several byproducts generated by automobiles and is believed to be a leading contributor to the so-called "greenhouse effect" linked to rising temperatures and climate change around the planet.

The amount of CO₂ in a given air sample is commonly expressed as parts-per-million (ppm) -- the number of molecules of carbon dioxide per million molecules. The outdoor air in most locations contains about 400-450 ppm carbon dioxide. Higher outdoor CO₂ concentrations can be found near vehicle traffic areas, industry and sources of combustion.

Where indoor concentrations are elevated (compared to the outside air) the source is usually the building's occupants. People exhale carbon dioxide -- the average adult's breath contains about 35,000 to 50,000 ppm of CO₂ (100 times higher than outdoor air). Without adequate ventilation to dilute and remove the CO₂ continuously generated by occupants, CO₂ can accumulate.

How do the CO₂ levels in a classroom increase or decrease during a class period?

Make a prediction - how do you think the CO₂ levels will change?

Variables:

Identify the type of data you will collect to support your hypothesis and state the manipulated, responding and controlled variables in this investigation.

When the file is opened, you should see a Graph Display of CO₂ vs. Time, as well as a digits display of CO₂.

Connect the CO₂ sensor to the USB Link. The sample rate has been set to take a measurement once every 15 seconds. Place the CO₂ Gas Sensor in an open area in the classroom. Wait approximately 30 seconds to allow the CO₂ reading to stabilize.

Step 4:

Data collection:

1. Click the Start button ( ) to begin collecting CO₂ data.
2. Be careful not to disturb the sensor during the experiment since sudden or excessive air movement, or CO₂ from breathing, will influence the results.
3. Click the Stop ( ) button to end the experiment near the end of the class period.
4. If possible, place the CO₂ sensor outside a window to collect a reading of outside air (if you are unable to go outside, typical outside air conditions are 400-450 ppm of CO₂).

Analyzing and Interpreting:

Scale the axes to fit the data using the "Scale to Fit" button (). Use the Note Tool () to annotate where on the graph any observed variables -- i.e., heater or A/C turned on/off, door or windows were opened/closed.

1.	Examine the graph and study the data. At what point was the CO2 reading the highest? The lowest? How did the results compare to your prediction?
2.	How would a reading from the first class period in the morning compare to one at the end of the day? Why?
3.	Are the readings you recorded in the classroom higher than the reading you obtained for outside air? Why?

Forming Conclusions:

4.	Based on the data you have collected, write a summary statement for the following question: How do the CO2 levels in a classroom increase or decrease during a class period?

Extending:

5.	One of the products of combustion of fossil fuels is C02. How do you think the levels of C02 change in a school parking lot when school is let out? Make a prediction, and design an experiment to test your prediction. Ensure your experiment is safe - stay well away from traffic.