Are the average carbon dioxide levels in cloth and surgical masks higher than government limits for CO2 in classrooms?
A lab study published in 2021 by the journal Aerosol and Air Quality Research measured CO2 levels in the breathing zones of a surgical mask and a 3-layer cloth mask. The study found that the average CO2 concentration was 2,051 parts per million (ppm) in the cloth mask, 2,107 ppm in the surgical mask, and 2,875 ppm in the surgical mask when the subject walked on a treadmill at a moderate pace. All of these levels are more than twice the 1,000 ppm long-term indoor limit for CO2 in many countries. The study notes that the CO2 levels found in the masks were in the "range" associated with the "health symptoms" of "sick building syndrome." The study was conducted in a well-ventilated lab with CO2 levels close to that of fresh air (400 ppm). In the real world, classroom CO2 levels are often much higher, and this may push the CO2 concentrations in the masks to well beyond what the study found.