Are O2 Levels in the Lower Atmosphere Decreasing?

[nuby]

Are O2 levels dropping in our atmosphere? I read something a while ago that mentioned allergies are getting worse due to increasing CO2 levels in atmosphere, so I'm guessing O2 levels are dropping as well. I was in the mountains a week ago (out of a valley), and noticed how easier it is to breath probably due to increased O2 concentrations. But the difference between breathing valley air, and mountain air seems to be getting bigger.

 

[mgb_phys]

CO2 has 'only' gone up by 100ppm (0.01%) so even if it did you would have a job detecting a change of 0.01% in the amount of oxygen.