NAU Scientists Study COVID Risk On Campus With Simple CO2 Sensors

May 6, 2021

Public health guidelines say to avoid crowded indoor spaces during the pandemic. But as schools reopen and people head back to the office, experts are looking for ways to measure how risky it is to share space and air with others. Scientists at Northern Arizona University are trying out an idea: simple carbon dioxide sensors in classrooms and science labs around campus. There’s even one here at KNAU. Science reporter Melissa Sevigny spoke with biologist George Koch to learn more about the project and hear our results.

Credit Melissa Sevigny


So tell me about these CO2 sensors and what you’re really measuring with them.

What they’re measuring is the concentration of the gas carbon dioxide, which we exhale in our breath…. When we exhale, the air that comes out of our lungs has roughly 100 times the concentration of carbon dioxide as the outdoor air. If we’re in a small poorly ventilated room, our sitting around, even if we’re not very active, really increases that carbon dioxide level quite a bit.

You’re basically measuring, you can see whether the air that I’m breathing in has already been breathed out by somebody else.

Yeah, that’s a good way of thinking about it.

So we’ve had this sensor in the KNAU studio for a couple of weeks now, what have you noticed so far?

The KNAU room has some of the higher spikes, and occasionally the CEFNS Dean’s Office is vying for the highest CO2 levels that we’ve seen on campus…. These carbon dioxide levels themselves are not dangerous at the levels we’re seeing in your studio, or anywhere else on campus, but we don’t yet really know how to link them to the concentrations of aerosols that could potentially be carrying COVID virus.

But they are showing us that the room isn’t very well ventilated, right?

They’re showing up that the room isn’t well ventilated, which is not surprising given that the room is supposed to be soundproof and you want it all sealed up and quiet in there.

What other things can affect CO2 levels?

If there’s a gas stove on or a gas heater; for example, in a biology lab they might be using a Bunsen’s burner which is burning gas and producing some carbon dioxide…. It could also be that if a room is near an air intake to a building and that air intake is exposed to, say, a delivery truck that’s idling… that could give an artificial spike. Or a nonhuman animal respiring in the room, if you have your cat sitting on your warm computer, it’s going to contribute to all the metabolically produced CO2 in that room. Those sorts of things all add up.

What are you planning on doing next with this research? 

I think what we’re planning to do next is to continue sampling different rooms and getting hopefully a broader range of occupancy measurements…. The other thing we would like to do, because these little carbon dioxide sensors are pretty low cost, it would be great to have many, many more of them and really develop a network of these across campus so we can be looking at a much larger number of rooms and occupancy and ventilation conditions.

If you see with these sensors that there are some of these higher spikes in some of the buildings you’re checking, what’s the next step. What should we do about that?....Should we turn on a fan, or open a window?

I would say here on campus, yeah, I’d look for opportunities to move more air through our offices.

So if you hear a fan behind Morning Edition tomorrow, you’ll know someone got worried about it and turned one on.  

That’s right! But we’ve got to keep in mind these risks are only present if we have infected people… obviously the best thing is we’re all staying healthy, getting vaccinated, and not carrying any viruses around with us. Lacking perfect knowledge for us, this sems like a good approach, just to get better ventilation.

George, thank you for speaking with me today.

Thanks a lot Melissa.