Fluctuating carbon dioxide (co2) levels between day/night?

Thread Starter

MikeA

Joined Jan 20, 2013
316
I have a number of NDIR carbon dioxide (co2) sensors for general indoor air quality (IAQ) monitoring, and I notice that when the house is vacant, well ventilated, and there are no artificial sources of co2 production, the co2 level fluctuates between day and night.

I have some sensors that fluctuate 50 PPM, and some that go up to 100 PPM. This kind of suggests that different sensors have different compensation methods, and some work better than others. But looking at temperature and humidity, there is only mild, and significantly lagging correlation between co2 and temperature/humidity.

I tried to Google a little bit, if there are natural and measurable co2 fluctuations between day and night (flora don't consume co2 at night and it spikes?) but didn't find anything.
 

Audioguru again

Joined Oct 21, 2019
5,202
Cars with old fashioned internal combustion engines produce CO2 especially when there are millions of them in the daytime.
At night there are only a few cars and most are noisy and have their mufflers and pollution controls removed (plus they are lowered and have black glass).
 

MrSalts

Joined Apr 2, 2020
2,378
As dew forms each evening and humidity condenses on the ground, the CO2 gas preferentially dissolves into the liquid water and lowers the concentration in the gas (air).
 

Thread Starter

MikeA

Joined Jan 20, 2013
316
Cars with old fashioned internal combustion engines produce CO2 especially when there are millions of them in the daytime.
At night there are only a few cars and most are noisy and have their mufflers and pollution controls removed (plus they are lowered and have black glass).
My sensors peak around 7am though, and the low point is around 7pm. So I'm not sure about the human activity theory. Would daily production of co2 even stay in lower atmosphere and not have enough time to mix?
 

Thread Starter

MikeA

Joined Jan 20, 2013
316
As dew forms each evening and humidity condenses on the ground, the CO2 gas preferentially dissolves into the liquid water and lowers the concentration in the gas (air).
That would make sense if my peaks were at 7pm, and lows at 7am, when humidity is highest after a cool night. But the co2 readings are reversed.
 

MrSalts

Joined Apr 2, 2020
2,378
Cars with old fashioned internal combustion engines produce CO2 especially when there are millions of them in the daytime.
At night there are only a few cars and most are noisy and have their mufflers and pollution controls removed (plus they are lowered and have black glass).
How does that black glass change the CO2 levels?
 
Top