Oooooh, I see what you're saying. You can find sample points that are sufficiently far from sources/sinks that your local measurements are (essentially) just measuring the aggregate of the troposphere.

That's different from saying that a local measurement at an arbitrary location is representative. Ok, I'm onboard now that I understand what you're saying. I was just commenting that local measurements are not necessarily reflective of larger scale measurements (which it sounds like is accurate with the exception of a few selective spots where the local readings happen to be better reflections of the average).