Nine observations from carbon dioxide monitoring

Summary

Introduction In the first year of the COVID-19 pandemic I learned that we can estimate our level of risk by checking the concentration of carbon dioxide in the air, because when infected people breathe out virus aerosols, they also breathe out CO2. I recently wrote about some limitations on this technique, and tips for getting reliable information. I’ve been checking carbon dioxide levels for over three years now, and I’ve started to see patterns. I don’t have to keep checking the same places, because they have the same levels under similar conditions. Today I charged my carbon dioxide monitor for the first time in weeks, because I’m flying on a plane for the first time in almost two years. I’d like to share some of the things I’ve learned, so that you can benefit even if you haven’t been monitoring carbon dioxide on your own. Outdoor air helps reduce the chance of passing on respiratory diseases In a cafe with the door open and without We’ve known this for over a century, but my readings have confirmed it. I’ve been to at least two cafes on warm fall days when the front door is open, and gotten nice low carbon dioxide readings. I came back a few weeks later when it was colder and the door was closed, and I wouldn’t have taken my mask off in there during an outbreak! The pictures above show the readings from one cafe with the front door open and closed. It doesn’t have to be a door or a window that’s open. A good ventilation system can exchange infectious air for cleaner outdoor air, or pass air through a filter that removes aerosols. The facilities manager at my employer is very proud of the ventilation system he’s set up, and the measurements I’ve taken show generally low concentrations of carbon dioxide across campus. I can feel the ventilation in certain hallways, like a stiff breeze. After these observations, if I see that there’s a window or a door open in a cafe, or if I can feel a breeze in a hallway, I have a good guess that it’s relatively safe. I might tr...