In April, the city of Peterborough became the first municipality in North America to facilitate such a program—loaning CO2 monitors to residents for a week at a time so they can determine the quality of ventilation inside their home, office or other indoor space .  places.
The devices use a “stop light system,” officials said at the time.  A green light means the air quality in the room is good, yellow means it’s OK, and red means there is minimal ventilation in the area.
The higher the indoor CO2 levels, the more recycled air a person will breathe.
“Good ventilation and filtration are important because they help reduce the risk of disease by reducing the levels of aerosols that contain viruses and bacteria, as well as other air quality concerns, that can make us sick, including the virus that causes COVID-19 Dr. Thomas Piggott, a Peterborough physician, said in a statement issued in April.
Piggott added that it is relatively easy to reduce CO2 levels if residents have a high output.  Actions such as opening windows, reducing the number of people in a room and using air filtration devices will help increase air ventilation.  Wearing a mask will also help remove potential pollutants in the air.
Around the same time the Peterborough program started, some residents approached the Toronto Public Library asking if they had plans to do something similar.  At the time, officials said on social media that they had been contacted by organizations interested in donating CO2 monitors and that updates would come at a later date.
Months later, it appears an official program may be in the works.
In a tweet posted on July 2, the library said it plans to introduce a CO2 monitoring program in mid-July, and more information is expected “in the coming weeks.”

		We will be introducing a CO2 monitoring loan program in mid-July as a pandemic response.  Look for more information in the coming weeks!  -PK
	— Toronto Public Library (@torontolibrary) July 2, 2022
CTV News Toronto reached out to the library for more details.
CO2 monitors have been widely used throughout the pandemic, although not consistently.  In 2021, Quebec’s education minister said screens will be installed in every classroom.
But when an Ontario Public Health Unit tried to enforce a policy that any classroom with a CO2 reading above 800 parts per million get an extra HEPA air filter, the province’s chief medical officer of health said experts “don’t are currently aware of any correlation between CO2 levels and virus transmission.”
The use of CO2 monitoring has been widely demonstrated in scientific journals as a tool to measure the risk of infection with COVID-19.