@shoshanahjacobs CO2 monitors work. My lecture hall at University of Waterloo where I teach 200 first years is usually about 700-750 ppm. One day it was 1500 ppm and I reported it to building services. They were awesome! Checked it out and ventilation was powered down. Was fixed by my next class! So easy - measure and report! #UniversityOfWaterloo #waterlooSci #RCH101 #airquality