Are atmospheric carbon dioxide levels consistent everywhere?

I imagine fluctuations in average atmospheric CO₂ ranges between the middle of a forest and the middle of a big city, but I have trouble conceptualizing the speed that a gas dissipates (using some approximation of the ideal gas law) vs. how large the atmosphere is on Earth, and whether the ~430ppm CO₂ is really a global average or a good approximation wherever you are on the planet.