Does being in the air provide any protection from an asteroid?
To answer the radiation question, it is both absorbed and reflected into space. A lot of these processes are complex relations between atmosphere, magnetosphere, and solar radiation. Solar radiation does penetrate through as it drives everything we need or any creature needs to live, whether directly or indirectly. Aurora Borealis is caused by Solar radiation trapped in our atmosphere. This is why Ozone (O3) is so important as it does a massive support function of helping block those rays. Some of this radiation is reflected by the earth as thermal radiation. The magnetosphere also plays a role in capturing and diffusing such particles. A little more research may help, it is a very fascinating process. For more:

https://en.wikipedia.org/wiki/Aurora

This was from courses in astronomy, hydrology, and my brain. Use wisely.