Over the summer I am continuing to play around with my new toy: a CO2 meter. This measures the carbon dioxide aka CO2 in the air. A plot of the CO2 concentration over one complete day (Thursday 11th August 2022) is shown above. This is in my bedroom. The units are ppm = parts per million, so 400 ppm means that out of every million molecules in the air, 400 are CO2.
The concentration of CO2 in the Earth’s atmosphere is shown as the green-dashed line above. It is a bit above 400 ppm. The concentration indoors where I am breathing out CO2 will always be higher than that. The concentration of CO2 in your, and my, breath is about 100 times higher than in the atmosphere.
If you look above, then starting in the early hours, you see a rapid increase to about 600 ppm, I think that is when I went to bed and closed the bigger windows, leaving smaller ones open for ventilation. Then the level slowly increases overnight, as the CO2 I breath out builds up a bit, but much less than it would it I closed all windows – see earlier post where I did that experiment. This increase sharply increases around 7 am-ish. This seems to occur all mornings, and is before I am up and about. It may be due to dawn meaning the sun is up and heating the air outside. If this increases the pressure outside, then that means direction of flow is mainly out to in, which is the wrong direction to remove CO2 from my home. But that is just a guess, I am no expert here.
The CO2 then drops as I open up windows in the morning to let air in, these are bigger windows than the ones left open overnight. Most of this drop is in less than an hour, so it looks like you only have to open up big windows for maybe 30 minutes to get rid of most of the CO2 and get fresh air in. In summer this does not matter as you want to keep the windows open all day, but in winter it may be useful to know.
The slope is still negative but small until around 1 pm when it jumps up. I worked from home with the windows open until then. I guess when I closed the windows when I went to work, CO2 moved from the front room where I was working into the bedroom. The CO2 concentration then dropped again when I came home and opened up the windows. I don’t know what caused the spike at around 5 pm is.
The concentration then drifts up slowly in the evening. The windows were all still open, so it may be that this due to most of the flow being out to in, or from the front room, where the CO2 source (me) is, to the bedroom. Anyway, building standards recommend ventilation that keeps CO2 below around 1000 ppm, so air quality on Thursday looks good. This is in summer of course, winter will be different as then you want to keep the heat in.