There are many, but the most important one is Mauna Loa. CO2 is well mixed in the atmosphere. It has to be or plant life would suffocate and die (remember CO2 i

There are many, but the most important one is Mauna Loa. CO2 is well mixed in the atmosphere. It has to be or plant life would suffocate and die (remember CO2 is their O2). Just like Oxygen is well mixed and evenly distributed around the planet. A ground measurement that is sufficiently isolated from forests or cities that could have localized effects is ideal. Muana is considered ideal because it sits out in the Pacific ocean on a remote island of Hawaii. https://www.co2.earth/22-co2-now/121-mauna-loa-co2 https://www.co2.earth/22-co2-now/121-mauna-loa-co2 For list of stations besides Mauna Loa: https://gml.noaa.gov/dv/site/ https://gml.noaa.gov/dv/site/