In order to find which type of UV light constitutes 95% of the UV light that hits the surface of the earth, let's consider the different types of ultraviolet (UV) radiation.
There are three main types of UV radiation classified based on their wavelength:
- UV-A: Wavelength between 320 and 400 nm.
- UV-B: Wavelength between 290 and 320 nm.
- UV-C: Wavelength between 100 and 290 nm.
The Earth's atmosphere, particularly the ozone layer, absorbs a significant portion of UV radiation from the sun. Here's a general summary of how these types of UV light are affected by the atmosphere:
- UV-C: Almost completely absorbed by the ozone layer and oxygen in the atmosphere.
- UV-B: Mostly absorbed by the ozone layer, but a small percentage reaches the Earth's surface.
- UV-A: Only minimally absorbed by the atmosphere, thus the majority of it reaches the Earth's surface.
Given that 95% of the UV light that reaches the Earth's surface is of a specific type, it must be the type that is least absorbed by the atmosphere. Based on the absorption characteristics:
- UV-C is almost entirely absorbed, so it cannot contribute significantly to the UV light at the surface.
- UV-B is partially absorbed, but it contributes a much smaller fraction compared to UV-A.
- UV-A has the least absorption by the atmosphere and hence constitutes the majority of the UV light reaching the surface.
Therefore, the type of UV light that makes up 95% of the UV light hitting the surface of the Earth is:
UV-A.
