Related to my previous question [When was the division between the troposphere and stratosphere determined?][1], an important atmospheric feature at this boundary is the Ozone Layer, as shown in the image below:

![enter image description here][2]

[Image source][3]

Given that the Ozone Layer concentration is very low, according to [NASA][4],  

> The peak concentration of ozone occurs at an altitude of roughly 32 kilometers (20 miles) above the surface of the Earth. At that altitude, ozone concentration can be as high as 15 parts per million (0.0015 percent).

**How was the Ozone Layer discovered?**


  [1]: http://hsm.stackexchange.com/questions/20/when-was-the-division-between-the-troposphere-and-stratosphere-determined
  [2]: https://i.sstatic.net/BNQcW.png
  [3]: https://www.nc-climate.ncsu.edu/edu/k12/.ozonelayer
  [4]: http://ozonewatch.gsfc.nasa.gov/facts/ozone.html