How does the air know from which direction the light is coming from?
As I said, the air is magnetoresonant horizontally. It will therefore only absorb the vertical component of the light's motion.
Are you serious? It's like you've just found a fancy word (and by the way "magnetoresonant", isn't a real word) and inserted it in a sentence without bothering to look up what it means.
Why isn't this true of all light? Why isn't this true of street lamps?
Why would you assume that it isn't?
It's not an assumption, it's an observation. Street lamps (and every other light source I have ever encountered) are noticably brighter when you get closer to them, regardless of whether or not the light is travelling vertically or horizontally or is over your head or beneath you or to your left or right.
Why hasn't this phenomenon been observed in experiments designed to test the visibility of air (and various other gasses)?
You'd have to ask the experimenters that.
I would, but I think I already know what their answer would be.
Most interestingly, if light from above is more readily "absorbed" why isn't the sky directly above my head a darker shade of blue?
Because it's closer to you. Ordinarily, it would be brighter, just as the Sun would overhead. This absorption causes it to appear more or less the same shade.
You seem to be having trouble grasping concepts like "closer" or "ordinary". The Sun is an object with a definite proximity to another object. The Sky is not - it's not a thing you can measure your distance from, so saying it's "closer to you" is meaningless. And why would the sky "ordinarily" be brighter, other than to validate your argument by means of circular logic?
And last of all, what makes this theory "obvious" or "simple"?
The fact that if the Sun would be brighter when overhead, and it is observed not to be, then something must be getting in the way of the light.
You're saying the solution to "why is the sun not brighter?" is obvious because the sun isn't brighter. When you hear yourself talk, does it make sense to
you?
I expected more from you, Parsifal.

Anyone else have any "serious" suggestions?