One of the most common environments with extremely high CO2 is in your car. Especially with the "recirculate" button on. Carbon dioxide levels over 1000 in general aren't good for your brain. Over 2000 can lead to drowsiness & more! 3 people in a car for a 30 minute commute hit 4500 this week 😱 If anyone was sick & unmasked, they would have easily spread their illness. Keep recirculate OFF whenever possible when driving & carpooling for safety & health! Masking up & open windows also help :)