Why do ultraviolet rays have difficulty reaching us through the atmosphere?

Why are ultraviolet and higher frequencies (x-ray, gamma-ray) difficult to pass through the atmosphere, and why are these rays the first wavelengths that begin to interact with cells? I’ll try to explain simply.

1. Fundamentals

Sun light is an electromagnetic wave. It carries energy, spread in space and behave like a wave or a particle. Famous physicist Einstein won Nobel prize with The photoelectric effect in which Light simultaneously possesses the characteristics of both waves and particles, each being manifested according to the circumstances.

The interaction of ultraviolet with cells comes from the photon property. Planck explained this with the equation e = hv. Here, E is the energy of each packet (or ‘quanta’) of light, measured in Joules. F is the frequency of light, measured in hertz; and h is of course Planck’s constant. Frequency of light increases, the energy of the photon increases linearly.

The light Spectrum

2. Why can’t high frequencies come through while visible light comes to us?

The structure of the earth, especially the atmosphere, is incredibly beautiful and protects us against all dangerous electromagnetic radiation. Gamma, x-rays, or ultraviolet light at very high frequencies act like a photon and are stopped by the ionosphere layer at the top of the atmosphere.

The energy carried by the sun light has a high enough energy to interact with the electron attached to the nitrogen and oxygen molecules and ionizes them all. During ionization, all the energy of the harmful light’s frequency is absorbed by the atoms, and electrons come out. Since the radiation from the sun is continuous, atoms are constantly ionizing. Hence, this layer is called the “ionosphere”.

The remaining light will continue to interact similarly in the ozone layer. Some of the remaining reflects back from various surfaces (clouds, mountains, shiny snowy surfaces) acting like a wave. Therefore, The higher you go, the more UV rays are exposed. It is found that UV rays increase by 10-12% for every 1000 meters.

Wavelengths that the human eye can perceive (between 400-700 nm) or low-frequency (uv-a) ultraviolet atoms reaching the earth’s surface are too low to ionize. Due to the non-ionizing, the filtered light can reach us. It is highly interesting that Nearly all of life forms found on earth are carbon-based and organic. Therefore, life is too fragile to be ionized by the incoming high frequencies and their damage.

UV rays types

2.1 Ultraviolet Frequencies (Wavelengths)

Ultraviolet (ultraviolet) also has a destructive effect on cells. Even the small amount of incoming ultraviolet light can harm us. Although there are many different ultraviolet radiation up to 10 nm wavelength (more lethal), here are the ones that interest us:

uvc = 100-290 nm
uvb = 290-320 nm
uva = 320-400 nm

2.2 Interaction of Ultraviolet and Human Skin

Luckily UV c does not reach us. Of UV b and UV a, about 10% of uvb and 40% of uva can reach human skin. The wavelength of these rays is absorbed from the skin a little, and it does not harm if it is not exposed for too long. Our skin also has melanin pigment that helps us in this regard. By absorbing the incoming ultraviolet light, it emits heat, and we get tan in return. But if you are exposed to it longer than necessary, it can penetrate deeper and break the bonds of the tissues, causing you to age.

For further readings, you may check uvlight, an continuous topic

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