Have you seen a car ad on television that shows the noisy chaos of the world outside the car before it pans to the driver inside the quiet, luxurious interior of said car, protected from the elements outside? The message you’re supposed to take from this juxtaposition is that this car is “tight”—sealed off from the world outside and all its perils. This sealing up is done for a few reasons: it provides a quiet interior, for sure, and it makes your air-conditioning and heating more efficient because the car is less “leaky.” But it also comes with an unexpected side effect: the pollutants inside the car have nowhere to go, leading to a buildup of potentially toxic pollutants emitted from materials inside the car, and a buildup of carbon dioxide emitted from the car’s occupants. We regularly see levels of CO2 inside cars that are as much as four to five times higher than what we allow in buildings. Ever get sleepy while on a long drive with the family or friends? The high carbon dioxide levels in your car are contributing to that—it’s one of the reasons you’ve likely heard the recommendation to roll down your windows if you feel sleepy while driving.