Interesting. What hardware do you use to measure this?

I have a Netatmo home device that measures PPM and have been observing the trend lines throughout the day. At some points my flat gets up to about 1400, which the device says is bad, and sometimes it goes down as low as 500. I've noticed a pattern but can't quite connect that pattern to my activity or the surroundings. It starts going up around 4pm, which could be homewards-bound vehicles, but it seems to trend even on weekends when there is lower traffic. Maybe I start breathing differently at these times. I'm quite interested in getting to the bottom of it. Unfortunately I'm west facing so plant use is quite limited.

What is the atmospheric ambient CO2 level? Is that variable based on location?

I've learnt a few things:

- I had my sensor on my work desk which meant the CO2 pooled, and was increased dramatically by my breathing almost directly onto it. Moved the sensor at least 1.5m

- I had the sensor quite low down, where CO2 pools (being heavier), so moved the sensor to eye level

- CO2 seemed to increase when cooking (same room), so while cooking I open the windows and let the warmth flow out of the building

Atmospheric CO2 is currently around 430 ppm. It's minimally variable based on seasonality, think a 15 ppm difference between the lowest and highest points.

It's been a long time since University for me but the standard measurement location is the Mauna (sp?) Loa Observatory in Hawaii, if I recall correctly due to it being the longest-running continuous measurement site.

By far the largest impact I’ve observed on my CO2 levels are from the hvac. When the fan is on the levels go down and tend to stay down, so I usually leave it on circulate which runs every ~15 mins (based on the graph structure). I use an SCD30 in the corner opposite to where I sit.

Also important is using a direct CO2 sensor (NDIR or photo acoustic) and not eco2 which can give false positives from other things in the air.