translation.en: Because when you go higher, the atmosphere is getting thinner, it's getting more unstable, the temperature is getting cooler, and you have a lot more U.V. radiation.
translation.zh: 因为当你到了更高处， 大气会变得更稀薄，更不稳定， 温度会降得更低， 你会得到更多的紫外线辐射。