How low in the stratosphere can I find Nitrogen?

Now I know that Earth has a total of around 78(ish)% of Nitrogen in the atmosphere.What I need to know is WHERE all that nitrogen lies. I need an answer in terms of volume with respect to altitude. And accurate answers would be much appreciated. Oh and if you have similar data on the <1% of Argon, please help me out. I'm a mechanical engineer so don't worry about simplifying terminology. I'll get it right off the bat. I just have too much research to do right now, to search for this particular data. Charts and graphs also accepted.