The stratosphere is mostly made up of nitrogen (N2) and oxygen (O2), just like the troposphere below it.

Here's a breakdown of the approximate composition:

* Nitrogen (N2): About 78%

* Oxygen (O2): About 21%

* Argon (Ar): About 1%

* Other trace gases: Includes carbon dioxide (CO2), neon (Ne), helium (He), methane (CH4), krypton (Kr), hydrogen (H2), and xenon (Xe).

It's important to note that the stratosphere also contains the ozone layer, which is a region with a higher concentration of ozone (O3) than other parts of the atmosphere. This ozone layer is crucial because it absorbs most of the Sun's harmful ultraviolet (UV) radiation.