A window into indoor air

 

"The coronavirus spreads through tiny, airborne droplets known as aerosols. Improving indoor ventilation reduces the concentration of these aerosols and the risk of infection in an indoor space, but there is no easy way for members of the public to measure the ventilation rate — let alone the accumulation of viral aerosols — in shared spaces.

“Ideally there’d be some machine that cost $100 and it starts beeping if the virus is in the air,” said Jose-Luis Jimenez, an aerosol scientist at the University of Colorado Boulder, who is sending a carbon dioxide monitor to school with his son. But in the absence of such a device, he said, “CO2 is something that provides an affordable and very meaningful shortcut.”

Every time we exhale, we expel not just aerosols but also carbon dioxide; the worse the ventilation, the more carbon dioxide builds up in an occupied room.

“If we see the CO2 rising, then that also implies that the concentration of aerosols are rising,” Dr. Huffman said. “Even just bringing sensor for a day or two can give you a really interesting and useful window into the world of the ventilation of that space.”

 

Ms. Norris and her husband are both science teachers, and so far their data suggest that the ventilation is excellent in both of their classrooms. But CO2 levels in her son’s classroom sometimes surpass 1300 parts per million. The C.D.C. recommends that indoor carbon dioxide levels remain below 800 p.p.m.

 

Children can still catch the virus in spaces with low CO2 levels and good ventilation. And high-quality air filters can trap viral aerosols, but have no effect on carbon dioxide levels. So in schools that have installed these filters, CO2 readings alone may overestimate the risk of viral transmission.

But even in the absence of the virus, reducing indoor carbon dioxide levels can have benefits. Studies show that even moderately high levels of the gas may muddle thinking and that improving ventilation can boost performance on cognitive tasks.

Of course, many families cannot afford a $100 air quality monitor — and they should not have to, parents and scientists said."