I see a lot of pictures on social media platforms where people measure Carbon Dioxide (CO2) concentrations in indoor environments incorrectly.
CO2 sensors are very sensitive instruments, and when you keep them close to your face they measure the CO2 concentrations of your breath and not of the room. The CO2 level in exhaled air is about 38,000ppm. When CO2 is exhaled it is quickly mixed with the ambient air and, if the ventilation is good, the concentration is quickly reduced to safe levels.
Keep the monitor away from your face, at least 3m/10ft. Preferable in a fixed point on the wall.
Composition of the air during inhaling & during exhaling
The typical composition of the inhaled air is:
- 78% Nitrogen
- 20.95% Oxygen
- 0.93% Argon
- 0.04% Carbon Dioxide
- 0.0005% Helium
- 0.00005% Hydrogen
- and small amounts of other gases
The gas exhaled is 3.8% to 5% by volume of CO2, about 100 times increase over the inhaled amount. The volume of oxygen is reduced by a small amount, 4% to 5%, compared to the oxygen inhaled.
The typical composition of the exhaled air is:
- 5.0–6.3% water vapor
- 79% Nitrogen
- 13.6–16.0% Oxygen
- 3.8–5.3% Carbon Dioxide
- 0.93% Argon
- ppm of Hydrogen, from the metabolic activity of microorganisms in the large intestine.
- ppm of Carbon Monoxide from degradation of heme proteins.
- 1 ppm of Ammonia.
- trace many hundreds of VOCs especially isoprene and acetone.
All in all, CO2 monitors are great tools that can help us mitigate the spread of an airborne virus but also ensure good ventilation rates and good air quality indoors. Unfortunately, many CO2 monitors don’t indicate that users should keep them at a distance while they are measuring the indoor concentrations.
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