It could be that you are living in the forest or a wooded area. The official measurement happens on Mauna Loa, purposefully chosen to be without vegetation or soil or nearby human activity.
> The observatory is surrounded by many miles of bare lava, without any vegetation or soil. This provides an opportunity to measure “background” air, also called “baseline”” air, which we define as having a CO2 mole fraction representative of an upwind fetch of hundreds of km. Nearby emission or removal of CO2 typically produces sharp fluctuations, in space and time, in mole fraction. These fluctuations get smoothed out with time and distance through turbulent mixing and wind shear. A distinguishing characteristic of background air is that CO2 changes only very gradually because the air has been mixed for days, without any significant additions or removals of CO2. Another common word for emissions is “sources”, and for removals, “sinks”.
> Volcanoes emit carbon dioxide in two ways: during eruptions and through underground magma. Carbon dioxide from underground magma is released through vents, porous rocks and soils, and water that feeds volcanic lakes and hot springs. Estimates of global carbon dioxide emissions from volcanoes have to take both erupted and non-erupted sources into account.
But there's still logistics problems when you have to evacuate the facility or the power supply is disrupted. Or is it somehow not an issue?
It's a yearly average. As the trees lose their leaves and they start to decompose the CO2 levels will spike. In the spring the CO2 levels will dip again, but when you average it out you can see the trendline pointing up.
Most (if not all) CO2 monitors need to be calibrated. The ones that I have looked into recommend putting it outside and calibrating it to 420ppm. I am not sure how much local variance in outdoor CO2 concentrations one can expect, but my guess is maybe 1-2ppm, definitely not 30ppm. But that is just a wild guess.
Your CO2 sensor is probably calibrated to 400 ppm. Most sensors auto calibrate to setting the lowest value over a period of time to some base value, usually 400 ppm.
If we built a habitable dome on Mars with a breathable atmosphere, Mars would still have a globally inhospitable atmosphere. Our key word "global" does not strictly mean every square inch of available space, but the overwhelming majority, which in this case also heavily impacts the remainder (such as requiring a habitable dome in the Mars example).
