Imagine a big blanket covering our Earth that protects us from space. This blanket is called the atmosphere. The atmosphere is made up of different layers, much like a layered cake. One of these layers is called the International Reference Atmosphere or IRA.
The IRA is like a recipe for what the atmosphere should be like at different heights. Just like how a recipe tells you how much of each ingredient to use, the IRA tells us what gases, like oxygen, nitrogen and others, should be found in each layer of the atmosphere. The IRA also tells us how thick each layer should be.
Scientists use this recipe to study the atmosphere, understand how it works and how it's changing over time. They can use it to make models and predictions about air pollution and climate change, as well as to design and test things like airplanes and rockets that have to fly through the different layers of the atmosphere.
So, even though you can't see it, the International Reference Atmosphere is really important because it helps us better understand and take care of our planet's atmosphere.