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

You’ve answered your own question there.

UVB rays can’t penetrate Clouds, so UVB ray levels will fluctuate based on the Seasons, ie in Fall and Winter you’re more likely to get cloud cover, so your exposure to UVB is reduced and with clearer skies in Spring and Summer it’s increased.

UVA rays can penetrate Clouds so remains constant throughout.