The ultraviolet (UV) component of sunlight that reaches the Earth's surface (terrestrial radiation) is composed of approximately 95% UVA and 5% UVB. The sun is the major source of human exposure to UVR.
Understanding Solar UV Radiation
The sun emits a range of electromagnetic radiation, including ultraviolet (UV) radiation. This UV radiation is categorized into three bands: UVA, UVB, and UVC. However, not all of this radiation reaches the Earth's surface due to absorption by the atmosphere. Here's a breakdown:
- UVA: This type of UV radiation has the longest wavelength and is the most abundant type reaching the Earth's surface.
- UVB: UVB has a shorter wavelength than UVA and is significantly absorbed by the ozone layer, meaning much less of it reaches the ground.
- UVC: The shortest wavelength of UV radiation is entirely absorbed by the atmosphere and does not reach the Earth's surface.
UV Composition at Earth's Surface
According to the provided reference, approximately 5% of solar radiation that reaches Earth's surface is UV radiation. Of this 5%, the majority is UVA, comprising about 95%, while UVB makes up approximately 5%. UVC does not reach the Earth's surface due to atmospheric absorption, particularly by the ozone layer.
| Type of UV Radiation | Percentage of Total UVR | Reach Earth's Surface? | Comments |
|---|---|---|---|
| UVA | ~95% | Yes | Most abundant type reaching Earth. |
| UVB | ~5% | Yes | Mostly absorbed by ozone, much less reaches surface |
| UVC | 0% | No | Completely absorbed by the atmosphere |
Key Takeaways
In summary, while the sun emits all types of UV radiation, only UVA and a small percentage of UVB reach the Earth's surface. The majority of UV exposure is through solar radiation.
- Approximately 5% of solar radiation reaching Earth is UV radiation.
- Of that UV radiation, ~95% is UVA, and ~5% is UVB.
- UVC does not reach the Earth's surface.
