The ozone layer, in the stratosphere, is where about 90% of the ozone in the Earth system is found. But ozone makes up only one to ten out of every million molecules in the ozone layer. There isn't much of it, but ozone is powerful, able to block the most harmful radiation.
This web series tells the story of the lengths people went to in order to explore the atmosphere and the technologies they used to get high in the sky and make measurements.