At Skeptical Science, they explain:
Mauna Loa is often used as an example of rising carbon dioxide levels because its the longest, continuous series of directly measured atmospheric CO₂. The reason why it's acceptable to use Mauna Loa as a proxy for global CO₂ levels is because CO₂ mixes well throughout the atmosphere.
This claim that Carbon Dioxide (CO2) mixes well in the atmosphere is repeated in other places: Example.
I am wondering if this is true and what data can prove it. I am skeptical because this fails for Ozone, for example - there are holes over Antarctica and sometimes the Arctic.