Which statement best describes UV-A radiation?

Which statement best describes UV-A radiation?

• A. UV-A penetrates deeply with less energy.
• B. UV-B is harmless and does not cause DNA damage.
• C. UV-C is the main form of sunlight reaching the Earth's surface.
• D. Ozone blocks all UV radiation equally.

Answer: (A)

UV radiation comes in bands with different wavelengths and effects. UV-A has the longest wavelength (about 315–400 nm) and carries less energy per photon than UV-B or UV-C. Because the atmosphere absorbs much of UV-C and a significant portion of UV-B, most UV that reaches the surface is UV-A. This form can penetrate deeply into the skin, reaching the dermis, and while it’s less likely to cause direct DNA damage than UV-B, it can still contribute to damage through reactive oxygen species and photoaging. In contrast, UV-B is more energetic and can directly damage DNA, causing sunburn and increasing cancer risk; UV-C is largely blocked by the ozone layer and atmosphere, so it doesn’t reach the surface in meaningful amounts. Ozone does not block all UV equally—UV-B and UV-C are absorbed much more strongly than UV-A.

UV radiation comes in bands with different wavelengths and effects. UV-A has the longest wavelength (about 315–400 nm) and carries less energy per photon than UV-B or UV-C. Because the atmosphere absorbs much of UV-C and a significant portion of UV-B, most UV that reaches the surface is UV-A. This form can penetrate deeply into the skin, reaching the dermis, and while it’s less likely to cause direct DNA damage than UV-B, it can still contribute to damage through reactive oxygen species and photoaging. In contrast, UV-B is more energetic and can directly damage DNA, causing sunburn and increasing cancer risk; UV-C is largely blocked by the ozone layer and atmosphere, so it doesn’t reach the surface in meaningful amounts. Ozone does not block all UV equally—UV-B and UV-C are absorbed much more strongly than UV-A.