Why does sunlight have ultraviolet rays? What's the harm to people?

Because sunlight is a kind of light source, including visible light and invisible light. Ultraviolet light is located outside purple light in the spectrum and is invisible light. Ultraviolet rays in sunlight are excited by electrons in the outer layer of atoms. The main ultraviolet light source in nature is the sun. When sunlight passes through the atmosphere, ultraviolet rays with wavelength less than 290nm are absorbed by ozone in the atmosphere.

Hazards of ultraviolet rays:

1. Ultraviolet rays are potentially harmful to human skin, such as sunburn, tanning and even cancer. UVA is the most carcinogenic among ultraviolet rays, and its red and sunburn effects are 1000 times that of UVB.

2. Ultraviolet radiation will cause skin to produce a large number of free radicals, which will lead to the peroxidation of cell membrane, and make melanocytes produce more melanin, which will be distributed upward to the stratum corneum of epidermis and produce black spots.

Ultraviolet rays can be said to be the biggest culprit of skin wrinkles, aging, relaxation and dark spots. ?

Extended data

Although ultraviolet rays are a little harmful to human body, they also have positive effects:

1, sterilization

Ultraviolet sterilization, short-wave ultraviolet is extremely destructive to microorganisms. When ultraviolet rays in this band irradiate bacteria, the nuclear protein and deoxyribonucleic acid (DNA) of cells strongly absorb the energy in this band, and the chain between them is opened and broken, which leads to the death of bacteria. Such as an ultraviolet mercury lamp or a metal halide lamp.

2. Health care function

Health care function of ultraviolet rays on human body. After the moon wave ultraviolet with the wavelength of 280 ~ 320 nm irradiates the human body, it can cause photochemical process and photoelectric reaction of the skin, and make the skin produce many active substances, thus playing a role in health care. Regular exposure to ultraviolet rays can enhance the phagocytosis of white blood cells and enhance people's immune function.

3. Promote the production of vitamins

Sunbathing is one source of vitamin D, and the other source is food. For example, ultraviolet rays in the sun are an important factor to promote the production of vitamin D by mushrooms, whether they are picked mushrooms or not. Therefore, fresh mushrooms should be dried and vitamin D supplementation is effective.

Step 4 decompose oil fume

The molecular chain of oil is changed by ultraviolet rays, and at the same time, this ultraviolet ray reacts with oxygen in the air to produce ozone, which will cool the oil molecules to produce carbon dioxide and water, and the organic matter in the oil fume is photooxidized and the odor is eliminated.

5, decomposition of organic matter

Adding (or coating) a small amount of nano titanium dioxide powder on the surface of building materials or household appliances can adsorb volatile organic compounds VOC (such as formaldehyde, benzene, toluene, ethanol, chloroform, etc. ), which can be decomposed after ultraviolet irradiation.

Baidu encyclopedia-ultraviolet