Could be due to cleaner operating cars in developed countrys.
http://news.softpedia.com/news/Atmospher...
but without context of the source of the question thats just a wild guess.
You need to start paying attention in class if you ever expect to learn anything.
Global Warming ended 11/28/2012 and it takes time for Nature to return all seasons to normal, but today most of you are too young to know how it was like 34 years ago before Global Warming. Mike
If the amount of CO2 has increased, that would produce a miniscule decrease in the percent of nitrogen.
It's my guess that your teacher has talked about nitrogen decline and you weren't listening.
I would question that they have changed. Without something to add or remove nitrogen from the atmosphere, nitrogen levels can't change.
Perhaps more recent measurements of atmospheric nitrogen are more accurate than older measurements.
putting it in tires
It's not so much the amount of nitrogen as the relative percentage compared to othe gases. The early atmosphere had little oxygen. Over time, with life nitrogen proportion to oxygen changed.
You can read the 'history of oxygen' for details
What nitrogen level change?
