Sitting in a traffic jam, your mind has time to wander. Always the scientific thinker, I began to wonder if increased CO₂ levels from the traffic were the cause of my incessant yawning on the way home from work. Would I be better off opening the windows and breathing the fumes of the cars around me or closing my vents and windows and breathing my own human exhaust? I was anxious to investigate.

I brought a Vernier CO₂ Gas Sensor and a LabPro interface in the car with me on my way home from work. I left the windows and vents open and proceeded to sit on the highway in stop-and-go traffic for 25 minutes. Surprisingly, to me at least, the CO₂ levels in the car stayed close to ambient at an average of 450 ppm (see Figure 1). The only slight rise came at minutes 20-22 when I was completely stopped with several big trucks around me.

Figure 1

Seeing so little change in CO₂ levels with the windows and vents open, I wondered what would happen if they were closed? I repeated my drive the next day with the windows and vents closed, and observed a rapid increase in CO₂ levels (see Figure 2). The concentration rose at an average rate of 80 ppm/min, then leveled off around 2700 ppm. The U.S. EPA states that CO₂ concentrations above 1000 ppm in buildings indicates a ventilation problem.¹ This is with only one person in the car. Imagine if the car was full of heavy breathers!

Figure 2

This led me to a third and final question: Does having the windows closed, but the vents open, provide enough fresh air to keep the CO₂ levels down? A third trip indicates the answer is yes (see Figure 3). The CO₂ concentration is constant at around 500 ppm. This is slightly above ambient, but is still in a healthy range.

Figure 3

What does all this mean? How does the size of the container affect concentration? What would happen if there were more people in the car? Is CO₂ the only exhaust product we should be concerned about? What are acceptable indoor CO₂ concentrations? What would happen to the O₂ concentration? This sounds like a great jumping off point for a student discussion and/or further research. As for me, I’m opening my vents and going home to get more sleep.

Reference
¹ Building Air Quality, EPA Publication No. 400/1-91/003