If UVB rays change in strength throughout the year why do UVA rays remain the same since both come from the sun?

Question

I live in the northern hemisphere and in my country we see a difference in UVB rays across the year, peaking in summer. So why does UVA stay the same over the year when they both come from the sun?

From the Skin Cancer Foundation

‘Ultraviolet B (UVB) rays, which are mainly responsible for sunburn, are the strongest in the summer.

Ultraviolet A (UVA) rays, which lead to tanning, dark spots and wrinkles, remain constant throughout the year and can penetrate through clouds and fog.’

In: 0

Answer 1

They are of two different wavelengths the UVA have the longest wavelength and UVB have a shorter wavelength in comparison.

UVA is about 90-95 % of the uv radiation from the sun while UVB is about 5%. That reaches the surface of the earth as UVB can be absorbed by the Ozone layer, while UVA doesn’t.

UVA have lower energy and penetrates the skin deeper than UVB.

UVB can be blocked by clouds and windows, UVA doesn’t usually.